--- /dev/null
+/*
+ * This file is part of the libsigrok project.
+ *
+ * Copyright (C) 2012 Alexandru Gagniuc <mr.nuke.me@gmail.com>
+ * Copyright (C) 2014 Aurelien Jacobs <aurel@gnuage.org>
+ * Copyright (C) 2019-2020 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/>.
+ */
+
+/**
+ * @file
+ *
+ * Protocol parser for Brymen BM850s DMM packets. The USB protocol (for the
+ * cable) and the packet description (for the meter) were retrieved from:
+ * http://brymen.com/product-html/Download2.html
+ * http://brymen.com/product-html/PD02BM850s_protocolDL.html
+ * http://brymen.com/product-html/images/DownloadList/ProtocolList/BM850-BM850a-BM850s_List/BM850-BM850a-BM850s-500000-count-DMM-protocol-BC85X-BC85Xa.zip
+ *
+ * Implementor's notes on the protocol:
+ * - The BM85x devices require a low RTS pulse after COM port open and
+ * before communication of requests and responses. The vendor doc
+ * recommends 100ms pulse width including delays around it. Without
+ * that RTS pulse the meter won't respond to requests.
+ * - The request has a three byte header (DLE, STX, command code), two
+ * bytes command arguments, and three bytes tail (checksum, DLE, ETX).
+ * The checksum spans the area (including) the command code and args.
+ * The checksum value is the XOR across all payload bytes. Exclusively
+ * command 0x00 is used (initiate next measurement response) which does
+ * not need arguments (passes all-zero values).
+ * - The response has a four byte header (DLE, STX, command code, payload
+ * size), the respective number of payload data bytes, and a three byte
+ * tail (checksum, DLE, ETX). The checksum spans the range after the
+ * length field and before the checksum field. Command 0 response data
+ * payload consists of a four byte flags field and a text field for
+ * measurement values (floating point with exponent in ASCII).
+ * - Special cases of response data:
+ * - The text field which carries the measurement value also contains
+ * whitespace which may break simple text to number conversion. Like
+ * 10 02 00 0f 07 00 00 00 20 30 2e 30 30 33 32 20 45 2b 30 46 10 03
+ * which translates to: 07 00 00 00 " 0.0032 E+0". Text for overload
+ * conditions can be shorter which results in variable packet length.
+ * Some meter functions provide unexpected text for their values.
+ * - The reference impedance for decibel measurements looks wrong and
+ * requires special treatment to isolate the 4..1200R value:
+ * bfunc 80 20 00 00, text " 0. 800 E+1" (reference, 800R)
+ * The decibel measurement values use an unexpected scale.
+ * bfunc 00 20 00 00, text "-0.3702 E-1" (measurement, -37.02dBm)
+ * The reference value gets sent (sometimes) in a DMM response when
+ * the meter's function is entered, or the reference value changes.
+ * The 'bfunc' flags combination allows telling packet types apart.
+ * - Temperature measurements put the C/F unit between the mantissa
+ * and the exponent, which needs to get removed: " 0.0217CE+3"
+ * - Diode measurements appear to exclusively provide the 'Volt' flag
+ * but no 'Diode' flag. The display shows ".diod" for a moment but
+ * this information is no longer available when voltage measurements
+ * are seen.
+ */
+
+#include <config.h>
+#include <ctype.h>
+#include <math.h>
+#include <libsigrok/libsigrok.h>
+#include "libsigrok-internal.h"
+#include <string.h>
+
+#define LOG_PREFIX "brymen-bm85x"
+
+#define STX 0x02
+#define ETX 0x03
+#define DLE 0x10
+
+#define CMD_GET_READING 0
+
+#define PKT_HEAD_LEN 4
+#define PKT_DATA_MAX 15
+#define PKT_TAIL_LEN 3
+#define PKT_BFUNC_LEN 4
+
+static uint8_t bm85x_crc(const uint8_t *buf, size_t len)
+{
+ uint8_t crc;
+
+ crc = 0;
+ while (len--)
+ crc ^= *buf++;
+
+ return crc;
+}
+
+#ifdef HAVE_SERIAL_COMM
+/** Meter's specific activity after port open and before data exchange. */
+SR_PRIV int brymen_bm85x_after_open(struct sr_serial_dev_inst *serial)
+{
+ int rts_toggle_delay_us;
+
+ /*
+ * The device requires an RTS *pulse* before communication.
+ * The vendor's documentation recommends the following sequence:
+ * Open the COM port, wait for 100ms, set RTS=1, wait for 100ms,
+ * set RTS=0, wait for 100ms, set RTS=1, configure bitrate and
+ * frame format, transmit request data, receive response data.
+ */
+ rts_toggle_delay_us = 100 * 1000; /* 100ms */
+ g_usleep(rts_toggle_delay_us);
+ serial_set_handshake(serial, 1, -1);
+ g_usleep(rts_toggle_delay_us);
+ serial_set_handshake(serial, 0, -1);
+ g_usleep(rts_toggle_delay_us);
+ serial_set_handshake(serial, 1, -1);
+ g_usleep(rts_toggle_delay_us);
+
+ return SR_OK;
+}
+
+static int bm85x_send_command(struct sr_serial_dev_inst *serial,
+ uint8_t cmd, uint8_t arg1, uint8_t arg2)
+{
+ uint8_t buf[8];
+ uint8_t crc, *wrptr, *crcptr;
+ size_t wrlen;
+ int ret;
+
+ wrptr = &buf[0];
+ write_u8_inc(&wrptr, DLE);
+ write_u8_inc(&wrptr, STX);
+ crcptr = wrptr;
+ write_u8_inc(&wrptr, cmd);
+ write_u8_inc(&wrptr, arg1);
+ write_u8_inc(&wrptr, arg2);
+ crc = bm85x_crc(crcptr, wrptr - crcptr);
+ write_u8_inc(&wrptr, crc);
+ write_u8_inc(&wrptr, DLE);
+ write_u8_inc(&wrptr, ETX);
+
+ wrlen = wrptr - &buf[0];
+ ret = serial_write_nonblocking(serial, &buf[0], wrlen);
+ if (ret < 0)
+ return ret;
+ if ((size_t)ret != wrlen)
+ return SR_ERR_IO;
+
+ return SR_OK;
+}
+
+/** Initiate reception of another meter's reading. */
+SR_PRIV int brymen_bm85x_packet_request(struct sr_serial_dev_inst *serial)
+{
+ return bm85x_send_command(serial, CMD_GET_READING, 0, 0);
+}
+#endif
+
+/**
+ * Check Brymen BM85x DMM packet for validity.
+ *
+ * @param[in] st The DMM driver's internal state.
+ * @param[in] buf The data bytes received so far.
+ * @param[in] len The received data's length (byte count).
+ * @param[out] pkt_len The packet's calculated total size (when valid).
+ *
+ * The BM850s protocol uses packets of variable length. A minimum amount
+ * of RX data provides the packet header, which communicates the payload
+ * size, which allows to determine the packet's total size. Callers of
+ * this validity checker can learn how much data will get consumed when
+ * a valid packet got received and processed. The packet size is not
+ * known in advance.
+ *
+ * @returns SR_OK when the packet is valid.
+ * @returns SR_ERR* (below zero) when the packet is invalid.
+ * @returns Greater 0 when packet is incomplete, more data is needed.
+ */
+SR_PRIV int brymen_bm85x_packet_valid(void *st,
+ const uint8_t *buf, size_t len, size_t *pkt_len)
+{
+ size_t plen;
+ uint8_t cmd, crc;
+
+ (void)st;
+
+ /* Four header bytes: DLE, STX, command, payload length. */
+ if (len < PKT_HEAD_LEN)
+ return SR_PACKET_NEED_RX;
+ if (read_u8_inc(&buf) != DLE)
+ return SR_PACKET_INVALID;
+ if (read_u8_inc(&buf) != STX)
+ return SR_PACKET_INVALID;
+ cmd = read_u8_inc(&buf);
+ /* Non-fatal, happens with OL pending during connect. */
+ if (cmd == 0x01)
+ cmd = 0x00;
+ if (cmd != CMD_GET_READING)
+ return SR_PACKET_INVALID;
+ plen = read_u8_inc(&buf);
+ if (plen > PKT_DATA_MAX)
+ return SR_PACKET_INVALID;
+ len -= PKT_HEAD_LEN;
+
+ /* Checksum spans bfunc and value text. Length according to header. */
+ if (len < plen + PKT_TAIL_LEN)
+ return SR_PACKET_NEED_RX;
+ crc = bm85x_crc(buf, plen);
+ buf += plen;
+ len -= plen;
+
+ /* Three tail bytes: checksum, DLE, ETX. */
+ if (len < PKT_TAIL_LEN)
+ return SR_PACKET_NEED_RX;
+ if (read_u8_inc(&buf) != crc)
+ return SR_PACKET_INVALID;
+ if (read_u8_inc(&buf) != DLE)
+ return SR_PACKET_INVALID;
+ if (read_u8_inc(&buf) != ETX)
+ return SR_PACKET_INVALID;
+
+ /*
+ * Only return the total packet length when the receive buffer
+ * was found to be valid. For invalid packets it's preferred to
+ * have the caller keep trying to sync to the packet stream.
+ */
+ if (pkt_len)
+ *pkt_len = PKT_HEAD_LEN + plen + PKT_TAIL_LEN;
+ return SR_PACKET_VALID;
+}
+
+struct bm85x_flags {
+ gboolean is_batt, is_db, is_perc, is_hz, is_amp, is_beep;
+ gboolean is_ohm, is_temp_f, is_temp_c, is_diode, is_cap;
+ gboolean is_volt, is_dc, is_ac;
+};
+
+static int bm85x_parse_flags(const uint8_t *bfunc, struct bm85x_flags *flags)
+{
+ if (!bfunc || !flags)
+ return SR_ERR_ARG;
+ memset(flags, 0, sizeof(*flags));
+
+ flags->is_batt = bfunc[3] & (1u << 7);
+ if ((bfunc[3] & 0x7f) != 0)
+ return SR_ERR_ARG;
+
+ if ((bfunc[2] & 0xff) != 0)
+ return SR_ERR_ARG;
+
+ if ((bfunc[1] & 0xc0) != 0)
+ return SR_ERR_ARG;
+ flags->is_db = bfunc[1] & (1u << 5);
+ if ((bfunc[1] & 0x10) != 0)
+ return SR_ERR_ARG;
+ flags->is_perc = bfunc[1] & (1u << 3);
+ flags->is_hz = bfunc[1] & (1u << 2);
+ flags->is_amp = bfunc[1] & (1u << 1);
+ flags->is_beep = bfunc[1] & (1u << 0);
+
+ flags->is_ohm = bfunc[0] & (1u << 7);
+ flags->is_temp_f = bfunc[0] & (1u << 6);
+ flags->is_temp_c = bfunc[0] & (1u << 5);
+ flags->is_diode = bfunc[0] & (1u << 4);
+ flags->is_cap = bfunc[0] & (1u << 3);
+ flags->is_volt = bfunc[0] & (1u << 2);
+ flags->is_dc = bfunc[0] & (1u << 1);
+ flags->is_ac = bfunc[0] & (1u << 0);
+
+ return SR_OK;
+}
+
+static int bm85x_parse_value(char *txt, double *val, int *digits)
+{
+ char *src, *dst, c;
+ int ret;
+
+ /*
+ * See above comment on whitespace in response's number text.
+ * The caller provides a NUL terminated writable text copy.
+ * Go for low hanging fruit first (OL condition). Eliminate
+ * whitespace then and do the number conversion.
+ */
+ if (strstr(txt, "+OL")) {
+ *val = +INFINITY;
+ return SR_OK;
+ }
+ if (strstr(txt, "-OL")) {
+ *val = -INFINITY;
+ return SR_OK;
+ }
+ if (strstr(txt, "OL")) {
+ *val = INFINITY;
+ return SR_OK;
+ }
+
+ src = txt;
+ dst = txt;
+ while (*src) {
+ c = *src++;
+ if (c == ' ')
+ continue;
+ *dst++ = c;
+ }
+ *dst = '\0';
+
+ ret = sr_atod_ascii_digits(txt, val, digits);
+ if (ret != SR_OK)
+ return ret;
+
+ return SR_OK;
+}
+
+static int bm85x_parse_payload(const uint8_t *p, size_t l,
+ double *val, struct sr_datafeed_analog *analog)
+{
+ const uint8_t *bfunc;
+ char text_buf[PKT_DATA_MAX], *text;
+ size_t text_len;
+ int ret;
+ struct bm85x_flags flags;
+ int digits;
+ char *parse;
+
+ /* Get a bfunc bits reference, and a writable value text. */
+ bfunc = &p[0];
+ text_len = l - PKT_BFUNC_LEN;
+ memcpy(text_buf, &p[PKT_BFUNC_LEN], text_len);
+ text_buf[text_len] = '\0';
+ text = &text_buf[0];
+ sr_dbg("DMM bfunc %02x %02x %02x %02x, text \"%s\"",
+ bfunc[0], bfunc[1], bfunc[2], bfunc[3], text);
+
+ /* Check 'bfunc' bitfield first, text interpretation depends on it. */
+ ret = bm85x_parse_flags(bfunc, &flags);
+ if (ret != SR_OK)
+ return ret;
+
+ /* Parse the text after potential normalization/transformation. */
+ if (flags.is_db && flags.is_ohm) {
+ static const char *prefix = " 0.";
+ static const char *suffix = " E";
+ /* See above comment on dBm reference value text. */
+ if (strncmp(text, prefix, strlen(prefix)) != 0)
+ return SR_ERR_DATA;
+ text += strlen(prefix);
+ text_len -= strlen(prefix);
+ parse = strstr(text, suffix);
+ if (!parse)
+ return SR_ERR_DATA;
+ *parse = '\0';
+ }
+ if (flags.is_temp_f || flags.is_temp_c) {
+ /* See above comment on temperature value text. */
+ parse = strchr(text, flags.is_temp_f ? 'F' : 'C');
+ if (!parse)
+ return SR_ERR_DATA;
+ *parse = ' ';
+ }
+ digits = 0;
+ ret = bm85x_parse_value(text, val, &digits);
+ if (ret != SR_OK)
+ return ret;
+
+ /* Fill in MQ and flags result details. */
+ analog->meaning->mqflags = 0;
+ if (flags.is_volt) {
+ analog->meaning->mq = SR_MQ_VOLTAGE;
+ analog->meaning->unit = SR_UNIT_VOLT;
+ }
+ if (flags.is_amp) {
+ analog->meaning->mq = SR_MQ_CURRENT;
+ analog->meaning->unit = SR_UNIT_AMPERE;
+ }
+ if (flags.is_ohm) {
+ if (flags.is_db)
+ analog->meaning->mq = SR_MQ_RESISTANCE;
+ else if (flags.is_beep)
+ analog->meaning->mq = SR_MQ_CONTINUITY;
+ else
+ analog->meaning->mq = SR_MQ_RESISTANCE;
+ analog->meaning->unit = SR_UNIT_OHM;
+ }
+ if (flags.is_hz) {
+ analog->meaning->mq = SR_MQ_FREQUENCY;
+ analog->meaning->unit = SR_UNIT_HERTZ;
+ }
+ if (flags.is_perc) {
+ analog->meaning->mq = SR_MQ_DUTY_CYCLE;
+ analog->meaning->unit = SR_UNIT_PERCENTAGE;
+ }
+ if (flags.is_cap) {
+ analog->meaning->mq = SR_MQ_CAPACITANCE;
+ analog->meaning->unit = SR_UNIT_FARAD;
+ }
+ if (flags.is_temp_f) {
+ analog->meaning->mq = SR_MQ_TEMPERATURE;
+ analog->meaning->unit = SR_UNIT_FAHRENHEIT;
+ }
+ if (flags.is_temp_c) {
+ analog->meaning->mq = SR_MQ_TEMPERATURE;
+ analog->meaning->unit = SR_UNIT_CELSIUS;
+ }
+ if (flags.is_db && !flags.is_ohm) {
+ /* See above comment on dBm measurements scale. */
+ analog->meaning->mq = SR_MQ_POWER;
+ analog->meaning->unit = SR_UNIT_DECIBEL_MW;
+ *val *= 1000;
+ digits -= 3;
+ }
+
+ if (flags.is_diode) {
+ /* See above comment on diode measurement responses. */
+ analog->meaning->mq = SR_MQ_VOLTAGE;
+ analog->meaning->unit = SR_UNIT_VOLT;
+ analog->meaning->mqflags |= SR_MQFLAG_DIODE;
+ analog->meaning->mqflags |= SR_MQFLAG_DC;
+ }
+ if (flags.is_ac)
+ analog->meaning->mqflags |= SR_MQFLAG_AC;
+ if (flags.is_dc)
+ analog->meaning->mqflags |= SR_MQFLAG_DC;
+
+ analog->encoding->digits = digits;
+ analog->spec->spec_digits = digits;
+
+ if (flags.is_batt)
+ sr_warn("Low battery!");
+
+ return SR_OK;
+}
+
+SR_PRIV int brymen_bm85x_parse(void *st, const uint8_t *buf, size_t len,
+ double *val, struct sr_datafeed_analog *analog, void *info)
+{
+ const uint8_t *pl_ptr;
+ size_t pl_len;
+
+ (void)st;
+ (void)info;
+
+ if (!buf || !len)
+ return SR_ERR_DATA;
+ if (!val || !analog)
+ return SR_ERR_DATA;
+
+ if (brymen_bm85x_packet_valid(NULL, buf, len, NULL) != SR_PACKET_VALID)
+ return SR_ERR_DATA;
+ pl_ptr = &buf[PKT_HEAD_LEN];
+ pl_len = len - PKT_HEAD_LEN - PKT_TAIL_LEN;
+
+ return bm85x_parse_payload(pl_ptr, pl_len, val, analog);
+}
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