[libsigrok.git] / src / hardware / asix-sigma / protocol.c

/*
 * This file is part of the libsigrok project.
 *
 * Copyright (C) 2010-2012 Håvard Espeland <gus@ping.uio.no>,
 * Copyright (C) 2010 Martin Stensgård <mastensg@ping.uio.no>
 * Copyright (C) 2010 Carl Henrik Lunde <chlunde@ping.uio.no>
 * Copyright (C) 2020 Gerhard Sittig <gerhard.sittig@gmx.net>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/*
 * ASIX SIGMA/SIGMA2 logic analyzer driver
 */

#include <config.h>
#include "protocol.h"

/*
 * The ASIX SIGMA hardware supports fixed 200MHz and 100MHz sample rates
 * (by means of separate firmware images). As well as 50MHz divided by
 * an integer divider in the 1..256 range (by the "typical" firmware).
 * Which translates to a strict lower boundary of around 195kHz.
 *
 * This driver "suggests" a subset of the available rates by listing a
 * few discrete values, while setter routines accept any user specified
 * rate that is supported by the hardware.
 */
static const uint64_t samplerates[] = {
        /* 50MHz and integer divider. 1/2/5 steps (where possible). */
        SR_KHZ(200), SR_KHZ(500),
        SR_MHZ(1), SR_MHZ(2), SR_MHZ(5),
        SR_MHZ(10), SR_MHZ(25), SR_MHZ(50),
        /* 100MHz/200MHz, fixed rates in special firmware. */
        SR_MHZ(100), SR_MHZ(200),
};

SR_PRIV GVariant *sigma_get_samplerates_list(void)
{
        return std_gvar_samplerates(samplerates, ARRAY_SIZE(samplerates));
}

static const char *firmware_files[] = {
        [SIGMA_FW_50MHZ] = "asix-sigma-50.fw", /* 50MHz, 8bit divider. */
        [SIGMA_FW_100MHZ] = "asix-sigma-100.fw", /* 100MHz, fixed. */
        [SIGMA_FW_200MHZ] = "asix-sigma-200.fw", /* 200MHz, fixed. */
        [SIGMA_FW_SYNC] = "asix-sigma-50sync.fw", /* Sync from external pin. */
        [SIGMA_FW_FREQ] = "asix-sigma-phasor.fw", /* Frequency counter. */
};

#define SIGMA_FIRMWARE_SIZE_LIMIT (256 * 1024)

static int sigma_ftdi_open(const struct sr_dev_inst *sdi)
{
        struct dev_context *devc;
        int vid, pid;
        const char *serno;
        int ret;

        devc = sdi->priv;
        if (!devc)
                return SR_ERR_ARG;

        if (devc->ftdi.is_open)
                return SR_OK;

        vid = devc->id.vid;
        pid = devc->id.pid;
        serno = sdi->serial_num;
        if (!vid || !pid || !serno || !*serno)
                return SR_ERR_ARG;

        ret = ftdi_init(&devc->ftdi.ctx);
        if (ret < 0) {
                sr_err("Cannot initialize FTDI context (%d): %s.",
                        ret, ftdi_get_error_string(&devc->ftdi.ctx));
                return SR_ERR_IO;
        }
        ret = ftdi_usb_open_desc_index(&devc->ftdi.ctx,
                vid, pid, NULL, serno, 0);
        if (ret < 0) {
                sr_err("Cannot open device (%d): %s.",
                        ret, ftdi_get_error_string(&devc->ftdi.ctx));
                return SR_ERR_IO;
        }
        devc->ftdi.is_open = TRUE;

        return SR_OK;
}

static int sigma_ftdi_close(struct dev_context *devc)
{
        int ret;

        ret = ftdi_usb_close(&devc->ftdi.ctx);
        devc->ftdi.is_open = FALSE;
        devc->ftdi.must_close = FALSE;
        ftdi_deinit(&devc->ftdi.ctx);

        return ret == 0 ? SR_OK : SR_ERR_IO;
}

SR_PRIV int sigma_check_open(const struct sr_dev_inst *sdi)
{
        struct dev_context *devc;
        int ret;

        if (!sdi)
                return SR_ERR_ARG;
        devc = sdi->priv;
        if (!devc)
                return SR_ERR_ARG;

        if (devc->ftdi.is_open)
                return SR_OK;

        ret = sigma_ftdi_open(sdi);
        if (ret != SR_OK)
                return ret;
        devc->ftdi.must_close = TRUE;

        return ret;
}

SR_PRIV int sigma_check_close(struct dev_context *devc)
{
        int ret;

        if (!devc)
                return SR_ERR_ARG;

        if (devc->ftdi.must_close) {
                ret = sigma_ftdi_close(devc);
                if (ret != SR_OK)
                        return ret;
                devc->ftdi.must_close = FALSE;
        }

        return SR_OK;
}

SR_PRIV int sigma_force_open(const struct sr_dev_inst *sdi)
{
        struct dev_context *devc;
        int ret;

        if (!sdi)
                return SR_ERR_ARG;
        devc = sdi->priv;
        if (!devc)
                return SR_ERR_ARG;

        ret = sigma_ftdi_open(sdi);
        if (ret != SR_OK)
                return ret;
        devc->ftdi.must_close = FALSE;

        return SR_OK;
}

SR_PRIV int sigma_force_close(struct dev_context *devc)
{
        return sigma_ftdi_close(devc);
}

/*
 * BEWARE! Error propagation is important, as are kinds of return values.
 *
 * - Raw USB tranport communicates the number of sent or received bytes,
 *   or negative error codes in the external library's(!) range of codes.
 * - Internal routines at the "sigrok driver level" communicate success
 *   or failure in terms of SR_OK et al error codes.
 * - Main loop style receive callbacks communicate booleans which arrange
 *   for repeated calls to drive progress during acquisition.
 *
 * Careful consideration by maintainers is essential, because all of the
 * above kinds of values are assignment compatbile from the compiler's
 * point of view. Implementation errors will go unnoticed at build time.
 */

static int sigma_read_raw(struct dev_context *devc, void *buf, size_t size)
{
        int ret;

        ret = ftdi_read_data(&devc->ftdi.ctx, (unsigned char *)buf, size);
        if (ret < 0) {
                sr_err("USB data read failed: %s",
                        ftdi_get_error_string(&devc->ftdi.ctx));
        }

        return ret;
}

static int sigma_write_raw(struct dev_context *devc, const void *buf, size_t size)
{
        int ret;

        ret = ftdi_write_data(&devc->ftdi.ctx, buf, size);
        if (ret < 0) {
                sr_err("USB data write failed: %s",
                        ftdi_get_error_string(&devc->ftdi.ctx));
        } else if ((size_t)ret != size) {
                sr_err("USB data write length mismatch.");
        }

        return ret;
}

static int sigma_read_sr(struct dev_context *devc, void *buf, size_t size)
{
        int ret;

        ret = sigma_read_raw(devc, buf, size);
        if (ret < 0 || (size_t)ret != size)
                return SR_ERR_IO;

        return SR_OK;
}

static int sigma_write_sr(struct dev_context *devc, const void *buf, size_t size)
{
        int ret;

        ret = sigma_write_raw(devc, buf, size);
        if (ret < 0 || (size_t)ret != size)
                return SR_ERR_IO;

        return SR_OK;
}

/*
 * Implementor's note: The local write buffer's size shall suffice for
 * any know FPGA register transaction that is involved in the supported
 * feature set of this sigrok device driver. If the length check trips,
 * that's a programmer's error and needs adjustment in the complete call
 * stack of the respective code path.
 */
#define SIGMA_MAX_REG_DEPTH     32

/*
 * Implementor's note: The FPGA command set supports register access
 * with automatic address adjustment. This operation is documented to
 * wrap within a 16-address range, it cannot cross boundaries where the
 * register address' nibble overflows. An internal helper assumes that
 * callers remain within this auto-adjustment range, and thus multi
 * register access requests can never exceed that count.
 */
#define SIGMA_MAX_REG_COUNT     16

SR_PRIV int sigma_write_register(struct dev_context *devc,
        uint8_t reg, uint8_t *data, size_t len)
{
        uint8_t buf[2 + SIGMA_MAX_REG_DEPTH * 2], *wrptr;
        size_t idx;

        if (len > SIGMA_MAX_REG_DEPTH) {
                sr_err("Short write buffer for %zu bytes to reg %u.", len, reg);
                return SR_ERR_BUG;
        }

        wrptr = buf;
        write_u8_inc(&wrptr, REG_ADDR_LOW | LO4(reg));
        write_u8_inc(&wrptr, REG_ADDR_HIGH | HI4(reg));
        for (idx = 0; idx < len; idx++) {
                write_u8_inc(&wrptr, REG_DATA_LOW | LO4(data[idx]));
                write_u8_inc(&wrptr, REG_DATA_HIGH_WRITE | HI4(data[idx]));
        }

        return sigma_write_sr(devc, buf, wrptr - buf);
}

SR_PRIV int sigma_set_register(struct dev_context *devc,
        uint8_t reg, uint8_t value)
{
        return sigma_write_register(devc, reg, &value, sizeof(value));
}

static int sigma_read_register(struct dev_context *devc,
        uint8_t reg, uint8_t *data, size_t len)
{
        uint8_t buf[3], *wrptr;
        int ret;

        wrptr = buf;
        write_u8_inc(&wrptr, REG_ADDR_LOW | LO4(reg));
        write_u8_inc(&wrptr, REG_ADDR_HIGH | HI4(reg));
        write_u8_inc(&wrptr, REG_READ_ADDR);
        ret = sigma_write_sr(devc, buf, wrptr - buf);
        if (ret != SR_OK)
                return ret;

        return sigma_read_sr(devc, data, len);
}

static int sigma_get_register(struct dev_context *devc,
        uint8_t reg, uint8_t *data)
{
        return sigma_read_register(devc, reg, data, sizeof(*data));
}

static int sigma_get_registers(struct dev_context *devc,
        uint8_t reg, uint8_t *data, size_t count)
{
        uint8_t buf[2 + SIGMA_MAX_REG_COUNT], *wrptr;
        size_t idx;
        int ret;

        if (count > SIGMA_MAX_REG_COUNT) {
                sr_err("Short command buffer for %zu reg reads at %u.", count, reg);
                return SR_ERR_BUG;
        }

        wrptr = buf;
        write_u8_inc(&wrptr, REG_ADDR_LOW | LO4(reg));
        write_u8_inc(&wrptr, REG_ADDR_HIGH | HI4(reg));
        for (idx = 0; idx < count; idx++)
                write_u8_inc(&wrptr, REG_READ_ADDR | REG_ADDR_INC);
        ret = sigma_write_sr(devc, buf, wrptr - buf);
        if (ret != SR_OK)
                return ret;

        return sigma_read_sr(devc, data, count);
}

static int sigma_read_pos(struct dev_context *devc,
        uint32_t *stoppos, uint32_t *triggerpos, uint8_t *mode)
{
        uint8_t result[7];
        const uint8_t *rdptr;
        uint32_t v32;
        uint8_t v8;
        int ret;

        /*
         * Read 7 registers starting at trigger position LSB.
         * Which yields two 24bit counter values, and mode flags.
         */
        ret = sigma_get_registers(devc, READ_TRIGGER_POS_LOW,
                result, sizeof(result));
        if (ret != SR_OK)
                return ret;

        rdptr = &result[0];
        v32 = read_u24le_inc(&rdptr);
        if (triggerpos)
                *triggerpos = v32;
        v32 = read_u24le_inc(&rdptr);
        if (stoppos)
                *stoppos = v32;
        v8 = read_u8_inc(&rdptr);
        if (mode)
                *mode = v8;

        /*
         * These positions consist of "the memory row" in the MSB fields,
         * and "an event index" within the row in the LSB fields. Part
         * of the memory row's content is sample data, another part is
         * timestamps.
         *
         * The retrieved register values point to after the captured
         * position. So they need to get decremented, and adjusted to
         * cater for the timestamps when the decrement carries over to
         * a different memory row.
         */
        if (stoppos && (--*stoppos & ROW_MASK) == ROW_MASK)
                *stoppos -= CLUSTERS_PER_ROW;
        if (triggerpos && (--*triggerpos & ROW_MASK) == ROW_MASK)
                *triggerpos -= CLUSTERS_PER_ROW;

        return SR_OK;
}

static int sigma_read_dram(struct dev_context *devc,
        size_t startchunk, size_t numchunks, uint8_t *data)
{
        uint8_t buf[128], *wrptr, regval;
        size_t chunk;
        int sel, ret;
        gboolean is_last;

        if (2 + 3 * numchunks > ARRAY_SIZE(buf)) {
                sr_err("Short write buffer for %zu DRAM row reads.", numchunks);
                return SR_ERR_BUG;
        }

        /* Communicate DRAM start address (memory row, aka samples line). */
        wrptr = buf;
        write_u16be_inc(&wrptr, startchunk);
        ret = sigma_write_register(devc, WRITE_MEMROW, buf, wrptr - buf);
        if (ret != SR_OK)
                return ret;

        /*
         * Access DRAM content. Fetch from DRAM to FPGA's internal RAM,
         * then transfer via USB. Interleave the FPGA's DRAM access and
         * USB transfer, use alternating buffers (0/1) in the process.
         */
        wrptr = buf;
        write_u8_inc(&wrptr, REG_DRAM_BLOCK);
        write_u8_inc(&wrptr, REG_DRAM_WAIT_ACK);
        for (chunk = 0; chunk < numchunks; chunk++) {
                sel = chunk % 2;
                is_last = chunk == numchunks - 1;
                if (!is_last) {
                        regval = REG_DRAM_BLOCK | REG_DRAM_SEL_BOOL(!sel);
                        write_u8_inc(&wrptr, regval);
                }
                regval = REG_DRAM_BLOCK_DATA | REG_DRAM_SEL_BOOL(sel);
                write_u8_inc(&wrptr, regval);
                if (!is_last)
                        write_u8_inc(&wrptr, REG_DRAM_WAIT_ACK);
        }
        ret = sigma_write_sr(devc, buf, wrptr - buf);
        if (ret != SR_OK)
                return ret;

        return sigma_read_sr(devc, data, numchunks * ROW_LENGTH_BYTES);
}

/* Upload trigger look-up tables to Sigma. */
SR_PRIV int sigma_write_trigger_lut(struct dev_context *devc,
        struct triggerlut *lut)
{
        size_t lut_addr;
        uint16_t bit;
        uint8_t m3d, m2d, m1d, m0d;
        uint8_t buf[6], *wrptr;
        uint8_t trgsel2;
        uint16_t lutreg, selreg;
        int ret;

        /*
         * Translate the LUT part of the trigger configuration from the
         * application's perspective to the hardware register's bitfield
         * layout. Send the LUT to the device. This configures the logic
         * which combines pin levels or edges.
         */
        for (lut_addr = 0; lut_addr < 16; lut_addr++) {
                bit = BIT(lut_addr);

                /* - M4 M3S M3Q */
                m3d = 0;
                if (lut->m4 & bit)
                        m3d |= BIT(2);
                if (lut->m3s & bit)
                        m3d |= BIT(1);
                if (lut->m3q & bit)
                        m3d |= BIT(0);

                /* M2D3 M2D2 M2D1 M2D0 */
                m2d = 0;
                if (lut->m2d[3] & bit)
                        m2d |= BIT(3);
                if (lut->m2d[2] & bit)
                        m2d |= BIT(2);
                if (lut->m2d[1] & bit)
                        m2d |= BIT(1);
                if (lut->m2d[0] & bit)
                        m2d |= BIT(0);

                /* M1D3 M1D2 M1D1 M1D0 */
                m1d = 0;
                if (lut->m1d[3] & bit)
                        m1d |= BIT(3);
                if (lut->m1d[2] & bit)
                        m1d |= BIT(2);
                if (lut->m1d[1] & bit)
                        m1d |= BIT(1);
                if (lut->m1d[0] & bit)
                        m1d |= BIT(0);

                /* M0D3 M0D2 M0D1 M0D0 */
                m0d = 0;
                if (lut->m0d[3] & bit)
                        m0d |= BIT(3);
                if (lut->m0d[2] & bit)
                        m0d |= BIT(2);
                if (lut->m0d[1] & bit)
                        m0d |= BIT(1);
                if (lut->m0d[0] & bit)
                        m0d |= BIT(0);

                /*
                 * Send 16bits with M3D/M2D and M1D/M0D bit masks to the
                 * TriggerSelect register, then strobe the LUT write by
                 * passing A3-A0 to TriggerSelect2. Hold RESET during LUT
                 * programming.
                 */
                wrptr = buf;
                lutreg = 0;
                lutreg <<= 4; lutreg |= m3d;
                lutreg <<= 4; lutreg |= m2d;
                lutreg <<= 4; lutreg |= m1d;
                lutreg <<= 4; lutreg |= m0d;
                write_u16be_inc(&wrptr, lutreg);
                ret = sigma_write_register(devc, WRITE_TRIGGER_SELECT,
                        buf, wrptr - buf);
                if (ret != SR_OK)
                        return ret;
                trgsel2 = TRGSEL2_RESET | TRGSEL2_LUT_WRITE |
                        (lut_addr & TRGSEL2_LUT_ADDR_MASK);
                ret = sigma_set_register(devc, WRITE_TRIGGER_SELECT2, trgsel2);
                if (ret != SR_OK)
                        return ret;
        }

        /*
         * Send the parameters. This covers counters and durations.
         */
        wrptr = buf;
        selreg = 0;
        selreg |= (lut->params.selinc & TRGSEL_SELINC_MASK) << TRGSEL_SELINC_SHIFT;
        selreg |= (lut->params.selres & TRGSEL_SELRES_MASK) << TRGSEL_SELRES_SHIFT;
        selreg |= (lut->params.sela & TRGSEL_SELA_MASK) << TRGSEL_SELA_SHIFT;
        selreg |= (lut->params.selb & TRGSEL_SELB_MASK) << TRGSEL_SELB_SHIFT;
        selreg |= (lut->params.selc & TRGSEL_SELC_MASK) << TRGSEL_SELC_SHIFT;
        selreg |= (lut->params.selpresc & TRGSEL_SELPRESC_MASK) << TRGSEL_SELPRESC_SHIFT;
        write_u16be_inc(&wrptr, selreg);
        write_u16be_inc(&wrptr, lut->params.cmpb);
        write_u16be_inc(&wrptr, lut->params.cmpa);
        ret = sigma_write_register(devc, WRITE_TRIGGER_SELECT, buf, wrptr - buf);
        if (ret != SR_OK)
                return ret;

        return SR_OK;
}

/*
 * See Xilinx UG332 for Spartan-3 FPGA configuration. The SIGMA device
 * uses FTDI bitbang mode for netlist download in slave serial mode.
 * (LATER: The OMEGA device's cable contains a more capable FTDI chip
 * and uses MPSSE mode for bitbang. -- Can we also use FT232H in FT245
 * compatible bitbang mode? For maximum code re-use and reduced libftdi
 * dependency? See section 3.5.5 of FT232H: D0 clk, D1 data (out), D2
 * data (in), D3 select, D4-7 GPIOL. See section 3.5.7 for MCU FIFO.)
 *
 * 750kbps rate (four times the speed of sigmalogan) works well for
 * netlist download. All pins except INIT_B are output pins during
 * configuration download.
 *
 * Some pins are inverted as a byproduct of level shifting circuitry.
 * That's why high CCLK level (from the cable's point of view) is idle
 * from the FPGA's perspective.
 *
 * The vendor's literature discusses a "suicide sequence" which ends
 * regular FPGA execution and should be sent before entering bitbang
 * mode and sending configuration data. Set D7 and toggle D2, D3, D4
 * a few times.
 */
#define BB_PIN_CCLK BIT(0) /* D0, CCLK */
#define BB_PIN_PROG BIT(1) /* D1, PROG */
#define BB_PIN_D2   BIT(2) /* D2, (part of) SUICIDE */
#define BB_PIN_D3   BIT(3) /* D3, (part of) SUICIDE */
#define BB_PIN_D4   BIT(4) /* D4, (part of) SUICIDE (unused?) */
#define BB_PIN_INIT BIT(5) /* D5, INIT, input pin */
#define BB_PIN_DIN  BIT(6) /* D6, DIN */
#define BB_PIN_D7   BIT(7) /* D7, (part of) SUICIDE */

#define BB_BITRATE (750 * 1000)
#define BB_PINMASK (0xff & ~BB_PIN_INIT)

/*
 * Initiate slave serial mode for configuration download. Which is done
 * by pulsing PROG_B and sensing INIT_B. Make sure CCLK is idle before
 * initiating the configuration download.
 *
 * Run a "suicide sequence" first to terminate the regular FPGA operation
 * before reconfiguration. The FTDI cable is single channel, and shares
 * pins which are used for data communication in FIFO mode with pins that
 * are used for FPGA configuration in bitbang mode. Hardware defaults for
 * unconfigured hardware, and runtime conditions after FPGA configuration
 * need to cooperate such that re-configuration of the FPGA can start.
 */
static int sigma_fpga_init_bitbang_once(struct dev_context *devc)
{
        const uint8_t suicide[] = {
                BB_PIN_D7 | BB_PIN_D2,
                BB_PIN_D7 | BB_PIN_D2,
                BB_PIN_D7 |           BB_PIN_D3,
                BB_PIN_D7 | BB_PIN_D2,
                BB_PIN_D7 |           BB_PIN_D3,
                BB_PIN_D7 | BB_PIN_D2,
                BB_PIN_D7 |           BB_PIN_D3,
                BB_PIN_D7 | BB_PIN_D2,
        };
        const uint8_t init_array[] = {
                BB_PIN_CCLK,
                BB_PIN_CCLK | BB_PIN_PROG,
                BB_PIN_CCLK | BB_PIN_PROG,
                BB_PIN_CCLK,
                BB_PIN_CCLK,
                BB_PIN_CCLK,
                BB_PIN_CCLK,
                BB_PIN_CCLK,
                BB_PIN_CCLK,
                BB_PIN_CCLK,
        };
        size_t retries;
        int ret;
        uint8_t data;

        /* Section 2. part 1), do the FPGA suicide. */
        ret = SR_OK;
        ret |= sigma_write_sr(devc, suicide, sizeof(suicide));
        ret |= sigma_write_sr(devc, suicide, sizeof(suicide));
        ret |= sigma_write_sr(devc, suicide, sizeof(suicide));
        ret |= sigma_write_sr(devc, suicide, sizeof(suicide));
        if (ret != SR_OK)
                return SR_ERR_IO;
        g_usleep(10 * 1000);

        /* Section 2. part 2), pulse PROG. */
        ret = sigma_write_sr(devc, init_array, sizeof(init_array));
        if (ret != SR_OK)
                return ret;
        g_usleep(10 * 1000);
        ftdi_usb_purge_buffers(&devc->ftdi.ctx);

        /*
         * Wait until the FPGA asserts INIT_B. Check in a maximum number
         * of bursts with a given delay between them. Read as many pin
         * capture results as the combination of FTDI chip and FTID lib
         * may provide. Cope with absence of pin capture data in a cycle.
         * This approach shall result in fast reponse in case of success,
         * low cost of execution during wait, reliable error handling in
         * the transport layer, and robust response to failure or absence
         * of result data (hardware inactivity after stimulus).
         */
        retries = 10;
        while (retries--) {
                do {
                        ret = sigma_read_raw(devc, &data, sizeof(data));
                        if (ret < 0)
                                return SR_ERR_IO;
                        if (ret == sizeof(data) && (data & BB_PIN_INIT))
                                return SR_OK;
                } while (ret == sizeof(data));
                if (retries)
                        g_usleep(10 * 1000);
        }

        return SR_ERR_TIMEOUT;
}

/*
 * This is belt and braces. Re-run the bitbang initiation sequence a few
 * times should first attempts fail. Failure is rare but can happen (was
 * observed during driver development).
 */
static int sigma_fpga_init_bitbang(struct dev_context *devc)
{
        size_t retries;
        int ret;

        retries = 10;
        while (retries--) {
                ret = sigma_fpga_init_bitbang_once(devc);
                if (ret == SR_OK)
                        return ret;
                if (ret != SR_ERR_TIMEOUT)
                        return ret;
        }
        return ret;
}

/*
 * Configure the FPGA for logic-analyzer mode.
 */
static int sigma_fpga_init_la(struct dev_context *devc)
{
        uint8_t buf[20], *wrptr;
        uint8_t data_55, data_aa, mode;
        uint8_t result[3];
        const uint8_t *rdptr;
        int ret;

        wrptr = buf;

        /* Read ID register. */
        write_u8_inc(&wrptr, REG_ADDR_LOW | LO4(READ_ID));
        write_u8_inc(&wrptr, REG_ADDR_HIGH | HI4(READ_ID));
        write_u8_inc(&wrptr, REG_READ_ADDR);

        /* Write 0x55 to scratch register, read back. */
        data_55 = 0x55;
        write_u8_inc(&wrptr, REG_ADDR_LOW | LO4(WRITE_TEST));
        write_u8_inc(&wrptr, REG_ADDR_HIGH | HI4(WRITE_TEST));
        write_u8_inc(&wrptr, REG_DATA_LOW | LO4(data_55));
        write_u8_inc(&wrptr, REG_DATA_HIGH_WRITE | HI4(data_55));
        write_u8_inc(&wrptr, REG_READ_ADDR);

        /* Write 0xaa to scratch register, read back. */
        data_aa = 0xaa;
        write_u8_inc(&wrptr, REG_ADDR_LOW | LO4(WRITE_TEST));
        write_u8_inc(&wrptr, REG_ADDR_HIGH | HI4(WRITE_TEST));
        write_u8_inc(&wrptr, REG_DATA_LOW | LO4(data_aa));
        write_u8_inc(&wrptr, REG_DATA_HIGH_WRITE | HI4(data_aa));
        write_u8_inc(&wrptr, REG_READ_ADDR);

        /* Initiate SDRAM initialization in mode register. */
        mode = WMR_SDRAMINIT;
        write_u8_inc(&wrptr, REG_ADDR_LOW | LO4(WRITE_MODE));
        write_u8_inc(&wrptr, REG_ADDR_HIGH | HI4(WRITE_MODE));
        write_u8_inc(&wrptr, REG_DATA_LOW | LO4(mode));
        write_u8_inc(&wrptr, REG_DATA_HIGH_WRITE | HI4(mode));

        /*
         * Send the command sequence which contains 3 READ requests.
         * Expect to see the corresponding 3 response bytes.
         */
        ret = sigma_write_sr(devc, buf, wrptr - buf);
        if (ret != SR_OK) {
                sr_err("Could not request LA start response.");
                return ret;
        }
        ret = sigma_read_sr(devc, result, ARRAY_SIZE(result));
        if (ret != SR_OK) {
                sr_err("Could not receive LA start response.");
                return SR_ERR_IO;
        }
        rdptr = result;
        if (read_u8_inc(&rdptr) != 0xa6) {
                sr_err("Unexpected ID response.");
                return SR_ERR_DATA;
        }
        if (read_u8_inc(&rdptr) != data_55) {
                sr_err("Unexpected scratch read-back (55).");
                return SR_ERR_DATA;
        }
        if (read_u8_inc(&rdptr) != data_aa) {
                sr_err("Unexpected scratch read-back (aa).");
                return SR_ERR_DATA;
        }

        return SR_OK;
}

/*
 * Read the firmware from a file and transform it into a series of bitbang
 * pulses used to program the FPGA. Note that the *bb_cmd must be free()'d
 * by the caller of this function.
 */
static int sigma_fw_2_bitbang(struct sr_context *ctx, const char *name,
        uint8_t **bb_cmd, size_t *bb_cmd_size)
{
        uint8_t *firmware;
        size_t file_size;
        uint8_t *p;
        size_t l;
        uint32_t imm;
        size_t bb_size;
        uint8_t *bb_stream, *bbs, byte, mask, v;

        /* Retrieve the on-disk firmware file content. */
        firmware = sr_resource_load(ctx, SR_RESOURCE_FIRMWARE, name,
                &file_size, SIGMA_FIRMWARE_SIZE_LIMIT);
        if (!firmware)
                return SR_ERR_IO;

        /* Unscramble the file content (XOR with "random" sequence). */
        p = firmware;
        l = file_size;
        imm = 0x3f6df2ab;
        while (l--) {
                imm = (imm + 0xa853753) % 177 + (imm * 0x8034052);
                *p++ ^= imm & 0xff;
        }

        /*
         * Generate a sequence of bitbang samples. With two samples per
         * FPGA configuration bit, providing the level for the DIN signal
         * as well as two edges for CCLK. See Xilinx UG332 for details
         * ("slave serial" mode).
         *
         * Note that CCLK is inverted in hardware. That's why the
         * respective bit is first set and then cleared in the bitbang
         * sample sets. So that the DIN level will be stable when the
         * data gets sampled at the rising CCLK edge, and the signals'
         * setup time constraint will be met.
         *
         * The caller will put the FPGA into download mode, will send
         * the bitbang samples, and release the allocated memory.
         */
        bb_size = file_size * 8 * 2;
        bb_stream = g_try_malloc(bb_size);
        if (!bb_stream) {
                sr_err("Memory allocation failed during firmware upload.");
                g_free(firmware);
                return SR_ERR_MALLOC;
        }
        bbs = bb_stream;
        p = firmware;
        l = file_size;
        while (l--) {
                byte = *p++;
                mask = 0x80;
                while (mask) {
                        v = (byte & mask) ? BB_PIN_DIN : 0;
                        mask >>= 1;
                        *bbs++ = v | BB_PIN_CCLK;
                        *bbs++ = v;
                }
        }
        g_free(firmware);

        /* The transformation completed successfully, return the result. */
        *bb_cmd = bb_stream;
        *bb_cmd_size = bb_size;

        return SR_OK;
}

static int upload_firmware(struct sr_context *ctx, struct dev_context *devc,
        enum sigma_firmware_idx firmware_idx)
{
        int ret;
        uint8_t *buf;
        uint8_t pins;
        size_t buf_size;
        const char *firmware;

        /* Check for valid firmware file selection. */
        if (firmware_idx >= ARRAY_SIZE(firmware_files))
                return SR_ERR_ARG;
        firmware = firmware_files[firmware_idx];
        if (!firmware || !*firmware)
                return SR_ERR_ARG;

        /* Avoid downloading the same firmware multiple times. */
        if (devc->firmware_idx == firmware_idx) {
                sr_info("Not uploading firmware file '%s' again.", firmware);
                return SR_OK;
        }

        devc->state = SIGMA_CONFIG;

        /* Set the cable to bitbang mode. */
        ret = ftdi_set_bitmode(&devc->ftdi.ctx, BB_PINMASK, BITMODE_BITBANG);
        if (ret < 0) {
                sr_err("Could not setup cable mode for upload: %s",
                        ftdi_get_error_string(&devc->ftdi.ctx));
                return SR_ERR;
        }
        ret = ftdi_set_baudrate(&devc->ftdi.ctx, BB_BITRATE);
        if (ret < 0) {
                sr_err("Could not setup bitrate for upload: %s",
                        ftdi_get_error_string(&devc->ftdi.ctx));
                return SR_ERR;
        }

        /* Initiate FPGA configuration mode. */
        ret = sigma_fpga_init_bitbang(devc);
        if (ret) {
                sr_err("Could not initiate firmware upload to hardware");
                return ret;
        }

        /* Prepare wire format of the firmware image. */
        ret = sigma_fw_2_bitbang(ctx, firmware, &buf, &buf_size);
        if (ret != SR_OK) {
                sr_err("Could not prepare file %s for upload.", firmware);
                return ret;
        }

        /* Write the FPGA netlist to the cable. */
        sr_info("Uploading firmware file '%s'.", firmware);
        ret = sigma_write_sr(devc, buf, buf_size);
        g_free(buf);
        if (ret != SR_OK) {
                sr_err("Could not upload firmware file '%s'.", firmware);
                return ret;
        }

        /* Leave bitbang mode and discard pending input data. */
        ret = ftdi_set_bitmode(&devc->ftdi.ctx, 0, BITMODE_RESET);
        if (ret < 0) {
                sr_err("Could not setup cable mode after upload: %s",
                        ftdi_get_error_string(&devc->ftdi.ctx));
                return SR_ERR;
        }
        ftdi_usb_purge_buffers(&devc->ftdi.ctx);
        while (sigma_read_raw(devc, &pins, sizeof(pins)) > 0)
                ;

        /* Initialize the FPGA for logic-analyzer mode. */
        ret = sigma_fpga_init_la(devc);
        if (ret != SR_OK) {
                sr_err("Hardware response after firmware upload failed.");
                return ret;
        }

        /* Keep track of successful firmware download completion. */
        devc->state = SIGMA_IDLE;
        devc->firmware_idx = firmware_idx;
        sr_info("Firmware uploaded.");

        return SR_OK;
}

/*
 * The driver supports user specified time or sample count limits. The
 * device's hardware supports neither, and hardware compression prevents
 * reliable detection of "fill levels" (currently reached sample counts)
 * from register values during acquisition. That's why the driver needs
 * to apply some heuristics:
 *
 * - The (optional) sample count limit and the (normalized) samplerate
 *   get mapped to an estimated duration for these samples' acquisition.
 * - The (optional) time limit gets checked as well. The lesser of the
 *   two limits will terminate the data acquisition phase. The exact
 *   sample count limit gets enforced in session feed submission paths.
 * - Some slack needs to be given to account for hardware pipelines as
 *   well as late storage of last chunks after compression thresholds
 *   are tripped. The resulting data set will span at least the caller
 *   specified period of time, which shall be perfectly acceptable.
 *
 * With RLE compression active, up to 64K sample periods can pass before
 * a cluster accumulates. Which translates to 327ms at 200kHz. Add two
 * times that period for good measure, one is not enough to flush the
 * hardware pipeline (observation from an earlier experiment).
 */
SR_PRIV int sigma_set_acquire_timeout(struct dev_context *devc)
{
        int ret;
        GVariant *data;
        uint64_t user_count, user_msecs;
        uint64_t worst_cluster_time_ms;
        uint64_t count_msecs, acquire_msecs;

        sr_sw_limits_init(&devc->limit.acquire);
        devc->late_trigger_timeout = FALSE;

        /* Get sample count limit, convert to msecs. */
        ret = sr_sw_limits_config_get(&devc->limit.config,
                SR_CONF_LIMIT_SAMPLES, &data);
        if (ret != SR_OK)
                return ret;
        user_count = g_variant_get_uint64(data);
        g_variant_unref(data);
        count_msecs = 0;
        if (devc->use_triggers) {
                user_count *= 100 - devc->capture_ratio;
                user_count /= 100;
        }
        if (user_count)
                count_msecs = 1000 * user_count / devc->clock.samplerate + 1;

        /* Get time limit, which is in msecs. */
        ret = sr_sw_limits_config_get(&devc->limit.config,
                SR_CONF_LIMIT_MSEC, &data);
        if (ret != SR_OK)
                return ret;
        user_msecs = g_variant_get_uint64(data);
        g_variant_unref(data);
        if (devc->use_triggers) {
                user_msecs *= 100 - devc->capture_ratio;
                user_msecs /= 100;
        }

        /* Get the lesser of them, with both being optional. */
        acquire_msecs = ~UINT64_C(0);
        if (user_count && count_msecs < acquire_msecs)
                acquire_msecs = count_msecs;
        if (user_msecs && user_msecs < acquire_msecs)
                acquire_msecs = user_msecs;
        if (acquire_msecs == ~UINT64_C(0))
                return SR_OK;

        /* Add some slack, and use that timeout for acquisition. */
        worst_cluster_time_ms = 1000 * 65536 / devc->clock.samplerate;
        acquire_msecs += 2 * worst_cluster_time_ms;
        data = g_variant_new_uint64(acquire_msecs);
        ret = sr_sw_limits_config_set(&devc->limit.acquire,
                SR_CONF_LIMIT_MSEC, data);
        g_variant_unref(data);
        if (ret != SR_OK)
                return ret;

        /* Deferred or immediate (trigger-less) timeout period start. */
        if (devc->use_triggers)
                devc->late_trigger_timeout = TRUE;
        else
                sr_sw_limits_acquisition_start(&devc->limit.acquire);

        return SR_OK;
}

/*
 * Check whether a caller specified samplerate matches the device's
 * hardware constraints (can be used for acquisition). Optionally yield
 * a value that approximates the original spec.
 *
 * This routine assumes that input specs are in the 200kHz to 200MHz
 * range of supported rates, and callers typically want to normalize a
 * given value to the hardware capabilities. Values in the 50MHz range
 * get rounded up by default, to avoid a more expensive check for the
 * closest match, while higher sampling rate is always desirable during
 * measurement. Input specs which exactly match hardware capabilities
 * remain unaffected. Because 100/200MHz rates also limit the number of
 * available channels, they are not suggested by this routine, instead
 * callers need to pick them consciously.
 */
SR_PRIV int sigma_normalize_samplerate(uint64_t want_rate, uint64_t *have_rate)
{
        uint64_t div, rate;

        /* Accept exact matches for 100/200MHz. */
        if (want_rate == SR_MHZ(200) || want_rate == SR_MHZ(100)) {
                if (have_rate)
                        *have_rate = want_rate;
                return SR_OK;
        }

        /* Accept 200kHz to 50MHz range, and map to near value. */
        if (want_rate >= SR_KHZ(200) && want_rate <= SR_MHZ(50)) {
                div = SR_MHZ(50) / want_rate;
                rate = SR_MHZ(50) / div;
                if (have_rate)
                        *have_rate = rate;
                return SR_OK;
        }

        return SR_ERR_ARG;
}

/* Gets called at probe time. Can seed software settings from hardware state. */
SR_PRIV int sigma_fetch_hw_config(const struct sr_dev_inst *sdi)
{
        struct dev_context *devc;
        int ret;
        uint8_t regaddr, regval;

        devc = sdi->priv;
        if (!devc)
                return SR_ERR_ARG;

        /* Seed configuration values from defaults. */
        devc->firmware_idx = SIGMA_FW_NONE;
        devc->clock.samplerate = samplerates[0];

        /* TODO
         * Ideally the device driver could retrieve recently stored
         * details from hardware registers, thus re-use user specified
         * configuration values across sigrok sessions. Which could
         * avoid repeated expensive though unnecessary firmware uploads,
         * improve performance and usability. Unfortunately it appears
         * that the registers range which is documented as available for
         * application use keeps providing 0xff data content. At least
         * with the netlist version which ships with sigrok. The same
         * was observed with unused registers in the first page.
         */
        return SR_ERR_NA;

        /* This is for research, currently does not work yet. */
        ret = sigma_check_open(sdi);
        regaddr = 16;
        regaddr = 14;
        ret = sigma_set_register(devc, regaddr, 'F');
        ret = sigma_get_register(devc, regaddr, &regval);
        sr_warn("%s() reg[%u] val[%u] rc[%d]", __func__, regaddr, regval, ret);
        ret = sigma_check_close(devc);
        return ret;
}

/* Gets called after successful (volatile) hardware configuration. */
SR_PRIV int sigma_store_hw_config(const struct sr_dev_inst *sdi)
{
        /* TODO See above, registers seem to not hold written data. */
        (void)sdi;
        return SR_ERR_NA;
}

SR_PRIV int sigma_set_samplerate(const struct sr_dev_inst *sdi)
{
        struct dev_context *devc;
        struct drv_context *drvc;
        uint64_t samplerate;
        int ret;
        size_t num_channels;

        devc = sdi->priv;
        drvc = sdi->driver->context;

        /* Accept any caller specified rate which the hardware supports. */
        ret = sigma_normalize_samplerate(devc->clock.samplerate, &samplerate);
        if (ret != SR_OK)
                return ret;

        /*
         * Depending on the samplerates of 200/100/50- MHz, specific
         * firmware is required and higher rates might limit the set
         * of available channels.
         */
        num_channels = devc->interp.num_channels;
        if (samplerate <= SR_MHZ(50)) {
                ret = upload_firmware(drvc->sr_ctx, devc, SIGMA_FW_50MHZ);
                num_channels = 16;
        } else if (samplerate == SR_MHZ(100)) {
                ret = upload_firmware(drvc->sr_ctx, devc, SIGMA_FW_100MHZ);
                num_channels = 8;
        } else if (samplerate == SR_MHZ(200)) {
                ret = upload_firmware(drvc->sr_ctx, devc, SIGMA_FW_200MHZ);
                num_channels = 4;
        }

        /*
         * The samplerate affects the number of available logic channels
         * as well as a sample memory layout detail (the number of samples
         * which the device will communicate within an "event").
         */
        if (ret == SR_OK) {
                devc->interp.num_channels = num_channels;
                devc->interp.samples_per_event = 16 / devc->interp.num_channels;
        }

        /*
         * Store the firmware type and most recently configured samplerate
         * in hardware, such that subsequent sessions can start from there.
         * This is a "best effort" approach. Failure is non-fatal.
         */
        if (ret == SR_OK)
                (void)sigma_store_hw_config(sdi);

        return ret;
}

/*
 * Arrange for a session feed submit buffer. A queue where a number of
 * samples gets accumulated to reduce the number of send calls. Which
 * also enforces an optional sample count limit for data acquisition.
 *
 * The buffer holds up to CHUNK_SIZE bytes. The unit size is fixed (the
 * driver provides a fixed channel layout regardless of samplerate).
 */

#define CHUNK_SIZE      (4 * 1024 * 1024)

struct submit_buffer {
        size_t unit_size;
        size_t max_samples, curr_samples;
        uint8_t *sample_data;
        uint8_t *write_pointer;
        struct sr_dev_inst *sdi;
        struct sr_datafeed_packet packet;
        struct sr_datafeed_logic logic;
};

static int alloc_submit_buffer(struct sr_dev_inst *sdi)
{
        struct dev_context *devc;
        struct submit_buffer *buffer;
        size_t size;

        devc = sdi->priv;

        buffer = g_malloc0(sizeof(*buffer));
        devc->buffer = buffer;

        buffer->unit_size = sizeof(uint16_t);
        size = CHUNK_SIZE;
        size /= buffer->unit_size;
        buffer->max_samples = size;
        size *= buffer->unit_size;
        buffer->sample_data = g_try_malloc0(size);
        if (!buffer->sample_data)
                return SR_ERR_MALLOC;
        buffer->write_pointer = buffer->sample_data;
        sr_sw_limits_init(&devc->limit.submit);

        buffer->sdi = sdi;
        memset(&buffer->logic, 0, sizeof(buffer->logic));
        buffer->logic.unitsize = buffer->unit_size;
        buffer->logic.data = buffer->sample_data;
        memset(&buffer->packet, 0, sizeof(buffer->packet));
        buffer->packet.type = SR_DF_LOGIC;
        buffer->packet.payload = &buffer->logic;

        return SR_OK;
}

static int setup_submit_limit(struct dev_context *devc)
{
        struct sr_sw_limits *limits;
        int ret;
        GVariant *data;
        uint64_t total;

        limits = &devc->limit.submit;

        ret = sr_sw_limits_config_get(&devc->limit.config,
                SR_CONF_LIMIT_SAMPLES, &data);
        if (ret != SR_OK)
                return ret;
        total = g_variant_get_uint64(data);
        g_variant_unref(data);

        sr_sw_limits_init(limits);
        if (total) {
                data = g_variant_new_uint64(total);
                ret = sr_sw_limits_config_set(limits,
                        SR_CONF_LIMIT_SAMPLES, data);
                g_variant_unref(data);
                if (ret != SR_OK)
                        return ret;
        }

        sr_sw_limits_acquisition_start(limits);

        return SR_OK;
}

static void free_submit_buffer(struct dev_context *devc)
{
        struct submit_buffer *buffer;

        if (!devc)
                return;

        buffer = devc->buffer;
        if (!buffer)
                return;
        devc->buffer = NULL;

        g_free(buffer->sample_data);
        g_free(buffer);
}

static int flush_submit_buffer(struct dev_context *devc)
{
        struct submit_buffer *buffer;
        int ret;

        buffer = devc->buffer;

        /* Is queued sample data available? */
        if (!buffer->curr_samples)
                return SR_OK;

        /* Submit to the session feed. */
        buffer->logic.length = buffer->curr_samples * buffer->unit_size;
        ret = sr_session_send(buffer->sdi, &buffer->packet);
        if (ret != SR_OK)
                return ret;

        /* Rewind queue position. */
        buffer->curr_samples = 0;
        buffer->write_pointer = buffer->sample_data;

        return SR_OK;
}

static int addto_submit_buffer(struct dev_context *devc,
        uint16_t sample, size_t count)
{
        struct submit_buffer *buffer;
        struct sr_sw_limits *limits;
        int ret;

        buffer = devc->buffer;
        limits = &devc->limit.submit;
        if (!devc->use_triggers && sr_sw_limits_check(limits))
                count = 0;

        /*
         * Individually accumulate and check each sample, such that
         * accumulation between flushes won't exceed local storage, and
         * enforcement of user specified limits is exact.
         */
        while (count--) {
                write_u16le_inc(&buffer->write_pointer, sample);
                buffer->curr_samples++;
                if (buffer->curr_samples == buffer->max_samples) {
                        ret = flush_submit_buffer(devc);
                        if (ret != SR_OK)
                                return ret;
                }
                sr_sw_limits_update_samples_read(limits, 1);
                if (!devc->use_triggers && sr_sw_limits_check(limits))
                        break;
        }

        return SR_OK;
}

static void sigma_location_break_down(struct sigma_location *loc)
{

        loc->line = loc->raw / ROW_LENGTH_U16;
        loc->line += ROW_COUNT;
        loc->line %= ROW_COUNT;
        loc->cluster = loc->raw % ROW_LENGTH_U16;
        loc->event = loc->cluster % EVENTS_PER_CLUSTER;
        loc->cluster = loc->cluster / EVENTS_PER_CLUSTER;
}

static gboolean sigma_location_is_eq(struct sigma_location *loc1,
        struct sigma_location *loc2, gboolean with_event)
{

        if (!loc1 || !loc2)
                return FALSE;

        if (loc1->line != loc2->line)
                return FALSE;
        if (loc1->cluster != loc2->cluster)
                return FALSE;

        if (with_event && loc1->event != loc2->event)
                return FALSE;

        return TRUE;
}

/* Decrement the broken-down location fields (leave 'raw' as is). */
static void sigma_location_decrement(struct sigma_location *loc,
        gboolean with_event)
{

        if (!loc)
                return;

        if (with_event) {
                if (loc->event--)
                        return;
                loc->event = EVENTS_PER_CLUSTER - 1;
        }

        if (loc->cluster--)
                return;
        loc->cluster = CLUSTERS_PER_ROW - 1;

        if (loc->line--)
                return;
        loc->line = ROW_COUNT - 1;
}

static void sigma_location_increment(struct sigma_location *loc)
{

        if (!loc)
                return;

        if (++loc->event < EVENTS_PER_CLUSTER)
                return;
        loc->event = 0;
        if (++loc->cluster < CLUSTERS_PER_ROW)
                return;
        loc->cluster = 0;
        if (++loc->line < ROW_COUNT)
                return;
        loc->line = 0;
}

/*
 * Determine the position where to open the period of trigger match
 * checks. Setup an "impossible" location when triggers are not used.
 * Start from the hardware provided 'trig' position otherwise, and
 * go back a few clusters, but don't go before the 'start' position.
 */
static void rewind_trig_arm_pos(struct dev_context *devc, size_t count)
{
        struct sigma_sample_interp *interp;

        if (!devc)
                return;
        interp = &devc->interp;

        if (!devc->use_triggers) {
                interp->trig_arm.raw = ~0;
                sigma_location_break_down(&interp->trig_arm);
                return;
        }

        interp->trig_arm = interp->trig;
        while (count--) {
                if (sigma_location_is_eq(&interp->trig_arm, &interp->start, TRUE))
                        break;
                sigma_location_decrement(&interp->trig_arm, TRUE);
        }
}

static int alloc_sample_buffer(struct dev_context *devc,
        size_t stop_pos, size_t trig_pos, uint8_t mode)
{
        struct sigma_sample_interp *interp;
        gboolean wrapped;
        size_t alloc_size;

        interp = &devc->interp;

        /*
         * Either fetch sample memory from absolute start of DRAM to the
         * current write position. Or from after the current write position
         * to before the current write position, if the write pointer has
         * wrapped around at the upper DRAM boundary. Assume that the line
         * which most recently got written to is of unknown state, ignore
         * its content in the "wrapped" case.
         */
        wrapped = mode & RMR_ROUND;
        interp->start.raw = 0;
        interp->stop.raw = stop_pos;
        if (wrapped) {
                interp->start.raw = stop_pos;
                interp->start.raw >>= ROW_SHIFT;
                interp->start.raw++;
                interp->start.raw <<= ROW_SHIFT;
                interp->stop.raw = stop_pos;
                interp->stop.raw >>= ROW_SHIFT;
                interp->stop.raw--;
                interp->stop.raw <<= ROW_SHIFT;
        }
        interp->trig.raw = trig_pos;
        interp->iter.raw = 0;

        /* Break down raw values to line, cluster, event fields. */
        sigma_location_break_down(&interp->start);
        sigma_location_break_down(&interp->stop);
        sigma_location_break_down(&interp->trig);
        sigma_location_break_down(&interp->iter);

        /*
         * The hardware provided trigger location "is late" because of
         * latency in hardware pipelines. It points to after the trigger
         * condition match. Arrange for a software check of sample data
         * matches starting just a little before the hardware provided
         * location. The "4 clusters" distance is an arbitrary choice.
         */
        rewind_trig_arm_pos(devc, 4 * EVENTS_PER_CLUSTER);
        memset(&interp->trig_chk, 0, sizeof(interp->trig_chk));

        /* Determine which DRAM lines to fetch from the device. */
        memset(&interp->fetch, 0, sizeof(interp->fetch));
        interp->fetch.lines_total = interp->stop.line + 1;
        interp->fetch.lines_total -= interp->start.line;
        interp->fetch.lines_total += ROW_COUNT;
        interp->fetch.lines_total %= ROW_COUNT;
        interp->fetch.lines_done = 0;

        /* Arrange for chunked download, N lines per USB request. */
        interp->fetch.lines_per_read = 32;
        alloc_size = sizeof(devc->interp.fetch.rcvd_lines[0]);
        alloc_size *= devc->interp.fetch.lines_per_read;
        devc->interp.fetch.rcvd_lines = g_try_malloc0(alloc_size);
        if (!devc->interp.fetch.rcvd_lines)
                return SR_ERR_MALLOC;

        return SR_OK;
}

static uint16_t sigma_deinterlace_data_4x4(uint16_t indata, int idx);
static uint16_t sigma_deinterlace_data_2x8(uint16_t indata, int idx);

static int fetch_sample_buffer(struct dev_context *devc)
{
        struct sigma_sample_interp *interp;
        size_t count;
        int ret;
        const uint8_t *rdptr;
        uint16_t ts, data;

        interp = &devc->interp;

        /* First invocation? Seed the iteration position. */
        if (!interp->fetch.lines_done) {
                interp->iter = interp->start;
        }

        /* Get another set of DRAM lines in one read call. */
        count = interp->fetch.lines_total - interp->fetch.lines_done;
        if (count > interp->fetch.lines_per_read)
                count = interp->fetch.lines_per_read;
        ret = sigma_read_dram(devc, interp->iter.line, count,
                (uint8_t *)interp->fetch.rcvd_lines);
        if (ret != SR_OK)
                return ret;
        interp->fetch.lines_rcvd = count;
        interp->fetch.curr_line = &interp->fetch.rcvd_lines[0];

        /* First invocation? Get initial timestamp and sample data. */
        if (!interp->fetch.lines_done) {
                rdptr = (void *)interp->fetch.curr_line;
                ts = read_u16le_inc(&rdptr);
                data = read_u16le_inc(&rdptr);
                if (interp->samples_per_event == 4) {
                        data = sigma_deinterlace_data_4x4(data, 0);
                } else if (interp->samples_per_event == 2) {
                        data = sigma_deinterlace_data_2x8(data, 0);
                }
                interp->last.ts = ts;
                interp->last.sample = data;
        }

        return SR_OK;
}

static void free_sample_buffer(struct dev_context *devc)
{
        g_free(devc->interp.fetch.rcvd_lines);
        devc->interp.fetch.rcvd_lines = NULL;
        devc->interp.fetch.lines_per_read = 0;
}

/*
 * In 100 and 200 MHz mode, only a single pin rising/falling can be
 * set as trigger. In other modes, two rising/falling triggers can be set,
 * in addition to value/mask trigger for any number of channels.
 *
 * The Sigma supports complex triggers using boolean expressions, but this
 * has not been implemented yet.
 */
SR_PRIV int sigma_convert_trigger(const struct sr_dev_inst *sdi)
{
        struct dev_context *devc;
        struct sr_trigger *trigger;
        struct sr_trigger_stage *stage;
        struct sr_trigger_match *match;
        const GSList *l, *m;
        uint16_t channelbit;
        size_t trigger_set;

        devc = sdi->priv;
        memset(&devc->trigger, 0, sizeof(devc->trigger));
        devc->use_triggers = FALSE;
        trigger = sr_session_trigger_get(sdi->session);
        if (!trigger)
                return SR_OK;

        if (!ASIX_SIGMA_WITH_TRIGGER) {
                sr_warn("Trigger support is not implemented. Ignoring the spec.");
                return SR_OK;
        }

        trigger_set = 0;
        for (l = trigger->stages; l; l = l->next) {
                stage = l->data;
                for (m = stage->matches; m; m = m->next) {
                        match = m->data;
                        /* Ignore disabled channels with a trigger. */
                        if (!match->channel->enabled)
                                continue;
                        channelbit = BIT(match->channel->index);
                        if (devc->clock.samplerate >= SR_MHZ(100)) {
                                /* Fast trigger support. */
                                if (trigger_set) {
                                        sr_err("100/200MHz modes limited to single trigger pin.");
                                        return SR_ERR;
                                }
                                if (match->match == SR_TRIGGER_FALLING) {
                                        devc->trigger.fallingmask |= channelbit;
                                } else if (match->match == SR_TRIGGER_RISING) {
                                        devc->trigger.risingmask |= channelbit;
                                } else {
                                        sr_err("100/200MHz modes limited to edge trigger.");
                                        return SR_ERR;
                                }

                                trigger_set++;
                        } else {
                                /* Simple trigger support (event). */
                                if (match->match == SR_TRIGGER_ONE) {
                                        devc->trigger.simplevalue |= channelbit;
                                        devc->trigger.simplemask |= channelbit;
                                } else if (match->match == SR_TRIGGER_ZERO) {
                                        devc->trigger.simplevalue &= ~channelbit;
                                        devc->trigger.simplemask |= channelbit;
                                } else if (match->match == SR_TRIGGER_FALLING) {
                                        devc->trigger.fallingmask |= channelbit;
                                        trigger_set++;
                                } else if (match->match == SR_TRIGGER_RISING) {
                                        devc->trigger.risingmask |= channelbit;
                                        trigger_set++;
                                }

                                /*
                                 * Actually, Sigma supports 2 rising/falling triggers,
                                 * but they are ORed and the current trigger syntax
                                 * does not permit ORed triggers.
                                 */
                                if (trigger_set > 1) {
                                        sr_err("Limited to 1 edge trigger.");
                                        return SR_ERR;
                                }
                        }
                }
        }

        /* Keep track whether triggers are involved during acquisition. */
        devc->use_triggers = TRUE;

        return SR_OK;
}

static gboolean sample_matches_trigger(struct dev_context *devc, uint16_t sample)
{
        struct sigma_sample_interp *interp;
        uint16_t last_sample;
        struct sigma_trigger *t;
        gboolean simple_match, rising_match, falling_match;
        gboolean matched;

        /*
         * This logic is about improving the precision of the hardware
         * provided trigger match position. Software checks are only
         * required for a short range of samples, and only when a user
         * specified trigger condition was involved during acquisition.
         */
        if (!devc)
                return FALSE;
        if (!devc->use_triggers)
                return FALSE;
        interp = &devc->interp;
        if (!interp->trig_chk.armed)
                return FALSE;

        /*
         * Check if the current sample and its most recent transition
         * match the initially provided trigger condition. The data
         * must not fail either of the individual checks. Unused
         * trigger features remain neutral in the summary expression.
         */
        last_sample = interp->last.sample;
        t = &devc->trigger;
        simple_match = (sample & t->simplemask) == t->simplevalue;
        rising_match = ((last_sample & t->risingmask) == 0) &&
                        ((sample & t->risingmask) == t->risingmask);
        falling_match = ((last_sample & t->fallingmask) == t->fallingmask) &&
                        ((sample & t->fallingmask) == 0);
        matched = simple_match && rising_match && falling_match;

        return matched;
}

static int send_trigger_marker(struct dev_context *devc)
{
        int ret;

        ret = flush_submit_buffer(devc);
        if (ret != SR_OK)
                return ret;
        ret = std_session_send_df_trigger(devc->buffer->sdi);
        if (ret != SR_OK)
                return ret;

        return SR_OK;
}

static int check_and_submit_sample(struct dev_context *devc,
        uint16_t sample, size_t count)
{
        gboolean triggered;
        int ret;

        triggered = sample_matches_trigger(devc, sample);
        if (triggered) {
                send_trigger_marker(devc);
                devc->interp.trig_chk.matched = TRUE;
        }

        ret = addto_submit_buffer(devc, sample, count);
        if (ret != SR_OK)
                return ret;

        return SR_OK;
}

static void sigma_location_check(struct dev_context *devc)
{
        struct sigma_sample_interp *interp;

        if (!devc)
                return;
        interp = &devc->interp;

        /*
         * Manage the period of trigger match checks in software.
         * Start supervision somewhere before the hardware provided
         * location. Stop supervision after an arbitrary amount of
         * event slots, or when a match was found.
         */
        if (interp->trig_chk.armed) {
                interp->trig_chk.evt_remain--;
                if (!interp->trig_chk.evt_remain || interp->trig_chk.matched)
                        interp->trig_chk.armed = FALSE;
        }
        if (!interp->trig_chk.armed && !interp->trig_chk.matched) {
                if (sigma_location_is_eq(&interp->iter, &interp->trig_arm, TRUE)) {
                        interp->trig_chk.armed = TRUE;
                        interp->trig_chk.matched = FALSE;
                        interp->trig_chk.evt_remain = 8 * EVENTS_PER_CLUSTER;
                }
        }

        /*
         * Force a trigger marker when the software check found no match
         * yet while the hardware provided position was reached. This
         * very probably is a user initiated button press.
         */
        if (interp->trig_chk.armed) {
                if (sigma_location_is_eq(&interp->iter, &interp->trig, TRUE)) {
                        (void)send_trigger_marker(devc);
                        interp->trig_chk.matched = TRUE;
                }
        }
}

/*
 * Return the timestamp of "DRAM cluster".
 */
static uint16_t sigma_dram_cluster_ts(struct sigma_dram_cluster *cluster)
{
        return read_u16le((const uint8_t *)&cluster->timestamp);
}

/*
 * Return one 16bit data entity of a DRAM cluster at the specified index.
 */
static uint16_t sigma_dram_cluster_data(struct sigma_dram_cluster *cl, int idx)
{
        return read_u16le((const uint8_t *)&cl->samples[idx]);
}

/*
 * Deinterlace sample data that was retrieved at 100MHz samplerate.
 * One 16bit item contains two samples of 8bits each. The bits of
 * multiple samples are interleaved.
 */
static uint16_t sigma_deinterlace_data_2x8(uint16_t indata, int idx)
{
        uint16_t outdata;

        indata >>= idx;
        outdata = 0;
        outdata |= (indata >> (0 * 2 - 0)) & (1 << 0);
        outdata |= (indata >> (1 * 2 - 1)) & (1 << 1);
        outdata |= (indata >> (2 * 2 - 2)) & (1 << 2);
        outdata |= (indata >> (3 * 2 - 3)) & (1 << 3);
        outdata |= (indata >> (4 * 2 - 4)) & (1 << 4);
        outdata |= (indata >> (5 * 2 - 5)) & (1 << 5);
        outdata |= (indata >> (6 * 2 - 6)) & (1 << 6);
        outdata |= (indata >> (7 * 2 - 7)) & (1 << 7);
        return outdata;
}

/*
 * Deinterlace sample data that was retrieved at 200MHz samplerate.
 * One 16bit item contains four samples of 4bits each. The bits of
 * multiple samples are interleaved.
 */
static uint16_t sigma_deinterlace_data_4x4(uint16_t indata, int idx)
{
        uint16_t outdata;

        indata >>= idx;
        outdata = 0;
        outdata |= (indata >> (0 * 4 - 0)) & (1 << 0);
        outdata |= (indata >> (1 * 4 - 1)) & (1 << 1);
        outdata |= (indata >> (2 * 4 - 2)) & (1 << 2);
        outdata |= (indata >> (3 * 4 - 3)) & (1 << 3);
        return outdata;
}

static void sigma_decode_dram_cluster(struct dev_context *devc,
        struct sigma_dram_cluster *dram_cluster,
        size_t events_in_cluster)
{
        uint16_t tsdiff, ts, sample, item16;
        size_t count;
        size_t evt;

        /*
         * If this cluster is not adjacent to the previously received
         * cluster, then send the appropriate number of samples with the
         * previous values to the sigrok session. This "decodes RLE".
         *
         * These samples cannot match the trigger since they just repeat
         * the previously submitted data pattern. (This assumption holds
         * for simple level and edge triggers. It would not for timed or
         * counted conditions, which currently are not supported.)
         */
        ts = sigma_dram_cluster_ts(dram_cluster);
        tsdiff = ts - devc->interp.last.ts;
        if (tsdiff > 0) {
                sample = devc->interp.last.sample;
                count = tsdiff * devc->interp.samples_per_event;
                (void)check_and_submit_sample(devc, sample, count);
        }
        devc->interp.last.ts = ts + EVENTS_PER_CLUSTER;

        /*
         * Grab sample data from the current cluster and prepare their
         * submission to the session feed. Handle samplerate dependent
         * memory layout of sample data. Accumulation of data chunks
         * before submission is transparent to this code path, specific
         * buffer depth is neither assumed nor required here.
         */
        sample = 0;
        for (evt = 0; evt < events_in_cluster; evt++) {
                item16 = sigma_dram_cluster_data(dram_cluster, evt);
                if (devc->interp.samples_per_event == 4) {
                        sample = sigma_deinterlace_data_4x4(item16, 0);
                        check_and_submit_sample(devc, sample, 1);
                        devc->interp.last.sample = sample;
                        sample = sigma_deinterlace_data_4x4(item16, 1);
                        check_and_submit_sample(devc, sample, 1);
                        devc->interp.last.sample = sample;
                        sample = sigma_deinterlace_data_4x4(item16, 2);
                        check_and_submit_sample(devc, sample, 1);
                        devc->interp.last.sample = sample;
                        sample = sigma_deinterlace_data_4x4(item16, 3);
                        check_and_submit_sample(devc, sample, 1);
                        devc->interp.last.sample = sample;
                } else if (devc->interp.samples_per_event == 2) {
                        sample = sigma_deinterlace_data_2x8(item16, 0);
                        check_and_submit_sample(devc, sample, 1);
                        devc->interp.last.sample = sample;
                        sample = sigma_deinterlace_data_2x8(item16, 1);
                        check_and_submit_sample(devc, sample, 1);
                        devc->interp.last.sample = sample;
                } else {
                        sample = item16;
                        check_and_submit_sample(devc, sample, 1);
                        devc->interp.last.sample = sample;
                }
                sigma_location_increment(&devc->interp.iter);
                sigma_location_check(devc);
        }
}

/*
 * Decode chunk of 1024 bytes, 64 clusters, 7 events per cluster.
 * Each event is 20ns apart, and can contain multiple samples.
 *
 * For 200 MHz, events contain 4 samples for each channel, spread 5 ns apart.
 * For 100 MHz, events contain 2 samples for each channel, spread 10 ns apart.
 * For 50 MHz and below, events contain one sample for each channel,
 * spread 20 ns apart.
 */
static int decode_chunk_ts(struct dev_context *devc,
        struct sigma_dram_line *dram_line,
        size_t events_in_line)
{
        struct sigma_dram_cluster *dram_cluster;
        size_t clusters_in_line;
        size_t events_in_cluster;
        size_t cluster;

        clusters_in_line = events_in_line;
        clusters_in_line += EVENTS_PER_CLUSTER - 1;
        clusters_in_line /= EVENTS_PER_CLUSTER;

        /* For each full DRAM cluster. */
        for (cluster = 0; cluster < clusters_in_line; cluster++) {
                dram_cluster = &dram_line->cluster[cluster];

                /* The last cluster might not be full. */
                if ((cluster == clusters_in_line - 1) &&
                    (events_in_line % EVENTS_PER_CLUSTER)) {
                        events_in_cluster = events_in_line % EVENTS_PER_CLUSTER;
                } else {
                        events_in_cluster = EVENTS_PER_CLUSTER;
                }

                sigma_decode_dram_cluster(devc, dram_cluster,
                        events_in_cluster);
        }

        return SR_OK;
}

static int download_capture(struct sr_dev_inst *sdi)
{
        struct dev_context *devc;
        struct sigma_sample_interp *interp;
        uint32_t stoppos, triggerpos;
        uint8_t modestatus;
        int ret;
        size_t chunks_per_receive_call;

        devc = sdi->priv;
        interp = &devc->interp;

        /*
         * Check the mode register. Force stop the current acquisition
         * if it has not yet terminated before. Will block until the
         * acquisition stops, assuming that this won't take long. Should
         * execute exactly once, then keep finding its condition met.
         *
         * Ask the hardware to stop data acquisition. Reception of the
         * FORCESTOP request makes the hardware "disable RLE" (store
         * clusters to DRAM regardless of whether pin state changes) and
         * raise the POSTTRIGGERED flag.
         */
        ret = sigma_get_register(devc, READ_MODE, &modestatus);
        if (ret != SR_OK) {
                sr_err("Could not determine current device state.");
                return FALSE;
        }
        if (!(modestatus & RMR_POSTTRIGGERED)) {
                sr_info("Downloading sample data.");
                devc->state = SIGMA_DOWNLOAD;

                modestatus = WMR_FORCESTOP | WMR_SDRAMWRITEEN;
                ret = sigma_set_register(devc, WRITE_MODE, modestatus);
                if (ret != SR_OK)
                        return FALSE;
                do {
                        ret = sigma_get_register(devc, READ_MODE, &modestatus);
                        if (ret != SR_OK) {
                                sr_err("Could not poll for post-trigger state.");
                                return FALSE;
                        }
                } while (!(modestatus & RMR_POSTTRIGGERED));
        }

        /*
         * Switch the hardware from DRAM write (data acquisition) to
         * DRAM read (sample memory download). Prepare resources for
         * sample memory content retrieval. Should execute exactly once,
         * then keep finding its condition met.
         *
         * Get the current positions (acquisition write pointer, and
         * trigger match location). With disabled triggers, use a value
         * for the location that will never match during interpretation.
         * Determine which area of the sample memory to retrieve,
         * allocate a receive buffer, and setup counters/pointers.
         */
        if (!interp->fetch.lines_per_read) {
                ret = sigma_set_register(devc, WRITE_MODE, WMR_SDRAMREADEN);
                if (ret != SR_OK)
                        return FALSE;

                ret = sigma_read_pos(devc, &stoppos, &triggerpos, &modestatus);
                if (ret != SR_OK) {
                        sr_err("Could not query capture positions/state.");
                        return FALSE;
                }
                if (!devc->use_triggers)
                        triggerpos = ~0;
                if (!(modestatus & RMR_TRIGGERED))
                        triggerpos = ~0;

                ret = alloc_sample_buffer(devc, stoppos, triggerpos, modestatus);
                if (ret != SR_OK)
                        return FALSE;

                ret = alloc_submit_buffer(sdi);
                if (ret != SR_OK)
                        return FALSE;
                ret = setup_submit_limit(devc);
                if (ret != SR_OK)
                        return FALSE;
        }

        /*
         * Get another set of sample memory rows, and interpret its
         * content. Will execute as many times as it takes to complete
         * the memory region that the recent acquisition spans.
         *
         * The size of a receive call's workload and the main loop's
         * receive call poll period determine the UI responsiveness and
         * the overall transfer time for the sample memory content.
         */
        chunks_per_receive_call = 50;
        while (interp->fetch.lines_done < interp->fetch.lines_total) {
                size_t dl_events_in_line;

                /* Read another chunk of sample memory (several lines). */
                ret = fetch_sample_buffer(devc);
                if (ret != SR_OK)
                        return FALSE;

                /* Process lines of sample data. Last line may be short. */
                while (interp->fetch.lines_rcvd--) {
                        dl_events_in_line = EVENTS_PER_ROW;
                        if (interp->iter.line == interp->stop.line) {
                                dl_events_in_line = interp->stop.raw & ROW_MASK;
                        }
                        decode_chunk_ts(devc, interp->fetch.curr_line,
                                dl_events_in_line);
                        interp->fetch.curr_line++;
                        interp->fetch.lines_done++;
                }

                /* Keep returning to application code for large data sets. */
                if (!--chunks_per_receive_call) {
                        ret = flush_submit_buffer(devc);
                        if (ret != SR_OK)
                                return FALSE;
                        break;
                }
        }

        /*
         * Release previously allocated resources, and adjust state when
         * all of the sample memory was retrieved, and interpretation has
         * completed. Should execute exactly once.
         */
        if (interp->fetch.lines_done >= interp->fetch.lines_total) {
                ret = flush_submit_buffer(devc);
                if (ret != SR_OK)
                        return FALSE;
                free_submit_buffer(devc);
                free_sample_buffer(devc);

                ret = std_session_send_df_end(sdi);
                if (ret != SR_OK)
                        return FALSE;

                devc->state = SIGMA_IDLE;
                sr_dev_acquisition_stop(sdi);
        }

        return TRUE;
}

/*
 * Periodically check the Sigma status when in CAPTURE mode. This routine
 * checks whether the configured sample count or sample time have passed,
 * and will stop acquisition and download the acquired samples.
 */
static int sigma_capture_mode(struct sr_dev_inst *sdi)
{
        struct dev_context *devc;
        int ret;
        uint32_t stoppos, triggerpos;
        uint8_t mode;
        gboolean full, wrapped, triggered, complete;

        devc = sdi->priv;

        /*
         * Get and interpret current acquisition status. Some of these
         * thresholds are rather arbitrary.
         */
        ret = sigma_read_pos(devc, &stoppos, &triggerpos, &mode);
        if (ret != SR_OK)
                return FALSE;
        stoppos >>= ROW_SHIFT;
        full = stoppos >= ROW_COUNT - 2;
        wrapped = mode & RMR_ROUND;
        triggered = mode & RMR_TRIGGERED;
        complete = mode & RMR_POSTTRIGGERED;

        /*
         * Acquisition completed in the hardware? Start or continue
         * sample memory content download.
         * (Can user initiated button presses result in auto stop?
         * Will they "trigger", and later result in expired time limit
         * of post trigger conditions?)
         */
        if (complete)
                return download_capture(sdi);

        /*
         * Previously configured acquisition period exceeded? Start
         * sample download. Start the timeout period late when triggers
         * are used (unknown period from acquisition start to trigger
         * match).
         */
        if (sr_sw_limits_check(&devc->limit.acquire))
                return download_capture(sdi);
        if (devc->late_trigger_timeout && triggered) {
                sr_sw_limits_acquisition_start(&devc->limit.acquire);
                devc->late_trigger_timeout = FALSE;
        }

        /*
         * No trigger specified, and sample memory exhausted? Start
         * download (may otherwise keep acquiring, even for infinite
         * amounts of time without a user specified time/count limit).
         * This handles situations when users specify limits which
         * exceed the device's capabilities.
         */
        (void)full;
        if (!devc->use_triggers && wrapped)
                return download_capture(sdi);

        return TRUE;
}

SR_PRIV int sigma_receive_data(int fd, int revents, void *cb_data)
{
        struct sr_dev_inst *sdi;
        struct dev_context *devc;

        (void)fd;
        (void)revents;

        sdi = cb_data;
        devc = sdi->priv;

        if (devc->state == SIGMA_IDLE)
                return TRUE;

        /*
         * When the application has requested to stop the acquisition,
         * then immediately start downloading sample data. Continue a
         * previously initiated download until completion. Otherwise
         * keep checking configured limits which will terminate the
         * acquisition and initiate download.
         */
        if (devc->state == SIGMA_STOPPING)
                return download_capture(sdi);
        if (devc->state == SIGMA_DOWNLOAD)
                return download_capture(sdi);
        if (devc->state == SIGMA_CAPTURE)
                return sigma_capture_mode(sdi);

        return TRUE;
}

/* Build a LUT entry used by the trigger functions. */
static void build_lut_entry(uint16_t *lut_entry,
        uint16_t spec_value, uint16_t spec_mask)
{
        size_t quad, bitidx, ch;
        uint16_t quadmask, bitmask;
        gboolean spec_value_low, bit_idx_low;

        /*
         * For each quad-channel-group, for each bit in the LUT (each
         * bit pattern of the channel signals, aka LUT address), for
         * each channel in the quad, setup the bit in the LUT entry.
         *
         * Start from all-ones in the LUT (true, always matches), then
         * "pessimize the truthness" for specified conditions.
         */
        for (quad = 0; quad < 4; quad++) {
                lut_entry[quad] = ~0;
                for (bitidx = 0; bitidx < 16; bitidx++) {
                        for (ch = 0; ch < 4; ch++) {
                                quadmask = BIT(ch);
                                bitmask = quadmask << (quad * 4);
                                if (!(spec_mask & bitmask))
                                        continue;
                                /*
                                 * This bit is part of the spec. The
                                 * condition which gets checked here
                                 * (got checked in all implementations
                                 * so far) is uncertain. A bit position
                                 * in the current index' number(!) is
                                 * checked?
                                 */
                                spec_value_low = !(spec_value & bitmask);
                                bit_idx_low = !(bitidx & quadmask);
                                if (spec_value_low == bit_idx_low)
                                        continue;
                                lut_entry[quad] &= ~BIT(bitidx);
                        }
                }
        }
}

/* Add a logical function to LUT mask. */
static void add_trigger_function(enum triggerop oper, enum triggerfunc func,
        size_t index, gboolean neg, uint16_t *mask)
{
        int x[2][2], a, b, aset, bset, rset;
        size_t bitidx;

        /*
         * Beware! The x, a, b, aset, bset, rset variables strictly
         * require the limited 0..1 range. They are not interpreted
         * as logically true, instead bit arith is done on them.
         */

        /* Construct a pattern which detects the condition. */
        memset(x, 0, sizeof(x));
        switch (oper) {
        case OP_LEVEL:
                x[0][1] = 1;
                x[1][1] = 1;
                break;
        case OP_NOT:
                x[0][0] = 1;
                x[1][0] = 1;
                break;
        case OP_RISE:
                x[0][1] = 1;
                break;
        case OP_FALL:
                x[1][0] = 1;
                break;
        case OP_RISEFALL:
                x[0][1] = 1;
                x[1][0] = 1;
                break;
        case OP_NOTRISE:
                x[1][1] = 1;
                x[0][0] = 1;
                x[1][0] = 1;
                break;
        case OP_NOTFALL:
                x[1][1] = 1;
                x[0][0] = 1;
                x[0][1] = 1;
                break;
        case OP_NOTRISEFALL:
                x[1][1] = 1;
                x[0][0] = 1;
                break;
        }

        /* Transpose the pattern if the condition is negated. */
        if (neg) {
                size_t i, j;
                int tmp;

                for (i = 0; i < 2; i++) {
                        for (j = 0; j < 2; j++) {
                                tmp = x[i][j];
                                x[i][j] = x[1 - i][1 - j];
                                x[1 - i][1 - j] = tmp;
                        }
                }
        }

        /* Update the LUT mask with the function's condition. */
        for (bitidx = 0; bitidx < 16; bitidx++) {
                a = (bitidx & BIT(2 * index + 0)) ? 1 : 0;
                b = (bitidx & BIT(2 * index + 1)) ? 1 : 0;

                aset = (*mask & BIT(bitidx)) ? 1 : 0;
                bset = x[b][a];

                if (func == FUNC_AND || func == FUNC_NAND)
                        rset = aset & bset;
                else if (func == FUNC_OR || func == FUNC_NOR)
                        rset = aset | bset;
                else if (func == FUNC_XOR || func == FUNC_NXOR)
                        rset = aset ^ bset;
                else
                        rset = 0;

                if (func == FUNC_NAND || func == FUNC_NOR || func == FUNC_NXOR)
                        rset = 1 - rset;

                if (rset)
                        *mask |= BIT(bitidx);
                else
                        *mask &= ~BIT(bitidx);
        }
}

/*
 * Build trigger LUTs used by 50 MHz and lower sample rates for supporting
 * simple pin change and state triggers. Only two transitions (rise/fall) can be
 * set at any time, but a full mask and value can be set (0/1).
 */
SR_PRIV int sigma_build_basic_trigger(struct dev_context *devc,
        struct triggerlut *lut)
{
        uint16_t masks[2];
        size_t bitidx, condidx;
        uint16_t value, mask;

        /* Setup something that "won't match" in the absence of a spec. */
        memset(lut, 0, sizeof(*lut));
        if (!devc->use_triggers)
                return SR_OK;

        /* Start assuming simple triggers. Edges are handled below. */
        lut->m4 = 0xa000;
        lut->m3q = 0xffff;

        /* Process value/mask triggers. */
        value = devc->trigger.simplevalue;
        mask = devc->trigger.simplemask;
        build_lut_entry(lut->m2d, value, mask);

        /* Scan for and process rise/fall triggers. */
        memset(&masks, 0, sizeof(masks));
        condidx = 0;
        for (bitidx = 0; bitidx < 16; bitidx++) {
                mask = BIT(bitidx);
                value = devc->trigger.risingmask | devc->trigger.fallingmask;
                if (!(value & mask))
                        continue;
                if (condidx == 0)
                        build_lut_entry(lut->m0d, mask, mask);
                if (condidx == 1)
                        build_lut_entry(lut->m1d, mask, mask);
                masks[condidx++] = mask;
                if (condidx == ARRAY_SIZE(masks))
                        break;
        }

        /* Add glue logic for rise/fall triggers. */
        if (masks[0] || masks[1]) {
                lut->m3q = 0;
                if (masks[0] & devc->trigger.risingmask)
                        add_trigger_function(OP_RISE, FUNC_OR, 0, 0, &lut->m3q);
                if (masks[0] & devc->trigger.fallingmask)
                        add_trigger_function(OP_FALL, FUNC_OR, 0, 0, &lut->m3q);
                if (masks[1] & devc->trigger.risingmask)
                        add_trigger_function(OP_RISE, FUNC_OR, 1, 0, &lut->m3q);
                if (masks[1] & devc->trigger.fallingmask)
                        add_trigger_function(OP_FALL, FUNC_OR, 1, 0, &lut->m3q);
        }

        /* Triggertype: event. */
        lut->params.selres = TRGSEL_SELCODE_NEVER;
        lut->params.selinc = TRGSEL_SELCODE_LEVEL;
        lut->params.sela = 0; /* Counter >= CMPA && LEVEL */
        lut->params.cmpa = 0; /* Count 0 -> 1 already triggers. */

        return SR_OK;
}