2 * This file is part of the libsigrok project.
4 * Copyright (C) 2019 Gerhard Sittig <gerhard.sittig@gmx.net>
6 * This program is free software: you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation, either version 3 of the License, or
9 * (at your option) any later version.
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program. If not, see <http://www.gnu.org/licenses/>.
21 * This implements serial transport primitives for Victor DMM cables,
22 * which forward normal DMM chips' protocols, but scramble the data in
23 * the process of forwarding. Just undoing the cable's scrambling at
24 * the serial communication level allows full re-use of existing DMM
25 * drivers, instead of creating Victor DMM specific support code.
27 * The cable's scrambling is somewhat complex:
28 * - The order of bits within the bytes gets reversed.
29 * - The order of bytes within the packet gets shuffled (randomly).
30 * - The byte values randomly get mapped to other values by adding a
31 * sequence of magic values to packet's byte values.
32 * None of this adds any value to the DMM chip vendor's protocol. It's
33 * mere obfuscation and extra complexity for the receiving application.
38 #include <libsigrok/libsigrok.h>
39 #include "libsigrok-internal.h"
40 #include "serial_hid.h"
43 #define LOG_PREFIX "serial-victor"
45 #ifdef HAVE_SERIAL_COMM
51 * Support serial-over-HID, specifically the Victor 70/86 DMM cables.
54 #define VICTOR_DMM_PACKET_LENGTH 14
56 static const struct vid_pid_item vid_pid_items_victor[] = {
61 /* Reverse bits within a byte. */
62 static uint8_t bit_reverse(uint8_t b)
64 static const uint8_t rev_nibble[] = {
65 0x00, 0x08, 0x04, 0x0c, 0x02, 0x0a, 0x06, 0x0e,
66 0x01, 0x09, 0x05, 0x0d, 0x03, 0x0b, 0x07, 0x0f,
69 return (rev_nibble[(b >> 4) & 0xf]) |
70 (rev_nibble[b & 0xf] << 4);
74 * The cable receives data by means of HID reports (simple data stream,
75 * HID report encapsulation was already trimmed). Assume that received
76 * data "is aligned", cope with zero or one 14-byte packets here, but
77 * don't try to even bother with odd-length reception units. Also drop
78 * the "all-zero" packets here which victor_dmm_receive_data() used to
79 * eliminate at the device driver level in the past.
81 static int victor_unobfuscate(uint8_t *rx_buf, size_t rx_len,
84 static const uint8_t obfuscation[VICTOR_DMM_PACKET_LENGTH] = {
85 'j', 'o', 'd', 'e', 'n', 'x', 'u', 'n', 'i', 'c', 'k', 'x', 'i', 'a',
87 static const uint8_t shuffle[VICTOR_DMM_PACKET_LENGTH] = {
88 6, 13, 5, 11, 2, 7, 9, 8, 3, 10, 12, 0, 4, 1
95 if (sr_log_loglevel_get() >= SR_LOG_SPEW) {
96 txt = sr_hexdump_new(rx_buf, rx_len);
97 sr_spew("Received %zu bytes: %s.", rx_len, txt->str);
101 /* Pass unexpected data in verbatim form. */
102 if (rx_len != VICTOR_DMM_PACKET_LENGTH) {
103 memcpy(ret_buf, rx_buf, rx_len);
107 /* Check for and discard all-zero packets. */
109 for (idx = 0; is_zero && idx < VICTOR_DMM_PACKET_LENGTH; idx++) {
114 sr_dbg("Received all zeroes packet, discarding.");
119 * Unobfuscate data bytes by subtracting a magic pattern, shuffle
120 * the bits and bytes into the DMM chip's original order.
122 for (idx = 0; idx < VICTOR_DMM_PACKET_LENGTH; idx++) {
123 to_idx = VICTOR_DMM_PACKET_LENGTH - 1 - shuffle[idx];
124 ret_buf[to_idx] = bit_reverse(rx_buf[idx] - obfuscation[idx]);
127 if (sr_log_loglevel_get() >= SR_LOG_SPEW) {
128 txt = sr_hexdump_new(ret_buf, idx);
129 sr_spew("Deobfuscated: %s.", txt->str);
130 sr_hexdump_free(txt);
137 * Read into a local buffer, and unobfuscate into the caller's buffer.
138 * Always receive full DMM packets.
140 static int victor_read_bytes(struct sr_serial_dev_inst *serial,
141 uint8_t *data, int space, unsigned int timeout)
143 uint8_t buf[VICTOR_DMM_PACKET_LENGTH];
146 if (space != sizeof(buf))
148 rc = ser_hid_hidapi_get_data(serial, 0, buf, space, timeout);
149 if (rc == SR_ERR_TIMEOUT)
156 return victor_unobfuscate(buf, rc, data);
159 /* Victor DMM cables are read-only. Just pretend successful transmission. */
160 static int victor_write_bytes(struct sr_serial_dev_inst *serial,
161 const uint8_t *data, int size)
169 static struct ser_hid_chip_functions chip_victor = {
170 .chipname = "victor",
171 .chipdesc = "Victor DMM scrambler",
172 .vid_pid_items = vid_pid_items_victor,
173 .max_bytes_per_request = VICTOR_DMM_PACKET_LENGTH,
175 * The USB HID connection has no concept of UART bitrate or
176 * frame format. Silently ignore the parameters.
178 .set_params = std_dummy_set_params,
179 .read_bytes = victor_read_bytes,
180 .write_bytes = victor_write_bytes,
182 SR_PRIV struct ser_hid_chip_functions *ser_hid_chip_funcs_victor = &chip_victor;
186 SR_PRIV struct ser_hid_chip_functions *ser_hid_chip_funcs_victor = NULL;