ardupilot/libraries/AP_HAL/utility/srxl.cpp

298 lines
7.6 KiB
C++
Raw Normal View History

// -*- tab-width: 8; Mode: C++; c-basic-offset: 8; indent-tabs-mode: -*- t -*-
/*
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/>.
*/
/*
SRXL protocol decoder, tested against AR7700 SRXL port
Andrew Tridgell, September 2016
*/
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include "srxl.h"
/*
there are other SRXL varients, but we need some sample data before accepting them
*/
#define SRXL_MAX_CHANNELS 20
#define SRXL_HEAD_MARKER 0xA5
#define SRXL_NUM_BYTES 18
static uint8_t buffer[SRXL_NUM_BYTES];
static uint8_t buflen;
static uint64_t last_data_us;
static uint16_t channels[SRXL_MAX_CHANNELS];
static uint16_t max_channels;
/*
get SRXL crc16 for a set of bytes
*/
static uint16_t srxl_crc16(const uint8_t *bytes, uint8_t nbytes)
{
uint16_t crc = 0;
while (nbytes--) {
int i;
crc ^= (uint16_t)(*bytes++) << 8;
for (i = 0; i < 8; i++) {
crc = (crc & 0x8000) ? (crc << 1) ^ 0x1021 : (crc << 1);
}
}
return crc;
}
/*
decode a SRXL packet
*/
int srxl_decode(uint64_t timestamp_us, uint8_t byte, uint8_t *num_values, uint16_t *values, uint16_t max_values, bool *failsafe_state)
{
if (timestamp_us - last_data_us > 5000U || buflen == SRXL_NUM_BYTES) {
// we've seen a frame gap
if (buflen != 0) {
buflen = 0;
}
}
last_data_us = timestamp_us;
buffer[buflen++] = byte;
switch (buffer[0]) {
case SRXL_HEAD_MARKER:
break;
default:
// invalid packet, we don't support this format yet
return 2;
}
uint8_t expected_bytes = SRXL_NUM_BYTES;
if (buflen < expected_bytes) {
// more bytes pending
return 1;
}
uint16_t crc = srxl_crc16(buffer, buflen-2);
uint64_t crc2 = buffer[buflen-1] | (buffer[buflen-2]<<8);
if (crc != crc2) {
// bad CRC
return 4;
}
// up to 7 channel values per packet. Each channel value is 16
// bits, with 11 bits of data and 4 bits of channel number. The
// top bit indicates a special X-Plus channel
for (uint8_t i=0; i<7; i++) {
uint16_t b = buffer[i*2+2] << 8 | buffer[i*2+3];
uint16_t c = b >> 11; // channel number
int32_t v = b & 0x7FF;
if (b & 0x8000) {
//printf("bad data 0x%04x\n", b);
// bad data
return 2;
}
if (c == 12) {
// special handling for channel 12
// see http://www.deviationtx.com/forum/protocol-development/2088-18-channels-for-dsm2-dsmx?start=40
//printf("c12: 0x%x %02x %02x\n", (unsigned)(b>>9), (unsigned)buffer[0], (unsigned)buffer[1]);
v = (b & 0x1FF) << 2;
c = 10 + ((b >> 9) & 0x7);
if (buffer[1] & 1) {
c += 4;
}
#if 0
printf("b=0x%04x v=%u c=%u b[1]=0x%02x\n",
(unsigned)b, (unsigned)v, (unsigned)c, (unsigned)buffer[1]);
#endif
} else if (c > 12) {
// invalid
v = 0;
}
// if channel number if greater than 16 then it is a X-Plus
// channel. We don't yet know how to decode those. There is some information here:
// but we really need some sample data to confirm
if (c < SRXL_MAX_CHANNELS) {
v = (((v - 0x400) * 500) / 876) + 1500;
channels[c] = v;
if (c >= max_channels) {
max_channels = c+1;
}
}
//printf("%u:%u ", (unsigned)c, (unsigned)v);
}
//printf("\n");
*num_values = max_channels;
if (*num_values > max_values) {
*num_values = max_values;
}
memcpy(values, channels, (*num_values)*2);
// check failsafe bit, this goes low when connection to the
// transmitter is lost
*failsafe_state = ((buffer[1] & 2) == 0);
#if 0
for (uint8_t i=0; i<buflen; i++) {
printf("%02x ", (unsigned)buffer[i]);
}
printf("\n");
#endif
buflen = 0;
// success
return 0;
}
#ifdef TEST_MAIN_PROGRAM
/*
test harness for use under Linux with USB serial adapter
*/
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <time.h>
#include <unistd.h>
#include <stdlib.h>
#include <termios.h>
static uint64_t micros64(void)
{
struct timespec ts;
clock_gettime(CLOCK_MONOTONIC, &ts);
return 1.0e6*((ts.tv_sec + (ts.tv_nsec*1.0e-9)));
}
int main(int argc, const char *argv[])
{
int fd = open(argv[1], O_RDONLY);
if (fd == -1) {
perror(argv[1]);
exit(1);
}
struct termios options;
tcgetattr(fd, &options);
cfsetispeed(&options, B115200);
cfsetospeed(&options, B115200);
options.c_cflag &= ~(PARENB|CSTOPB|CSIZE);
options.c_cflag |= CS8;
options.c_lflag &= ~(ICANON|ECHO|ECHOE|ISIG);
options.c_iflag &= ~(IXON|IXOFF|IXANY);
options.c_oflag &= ~OPOST;
if (tcsetattr(fd, TCSANOW, &options) != 0) {
perror("tcsetattr");
exit(1);
}
tcflush(fd, TCIOFLUSH);
while (true) {
uint8_t b;
uint8_t num_values = 0;
uint16_t values[20];
bool failsafe_state;
fd_set fds;
struct timeval tv;
FD_ZERO(&fds);
FD_SET(fd, &fds);
tv.tv_sec = 1;
tv.tv_usec = 0;
// check if any bytes are available
if (select(fd+1, &fds, NULL, NULL, &tv) != 1) {
break;
}
if (read(fd, &b, 1) != 1) {
break;
}
if (srxl_decode(micros64(), b, &num_values, values, sizeof(values)/sizeof(values[0]), &failsafe_state) == 0) {
#if 1
printf("%u: ", num_values);
for (uint8_t i=0; i<num_values; i++) {
printf("%u:%4u ", i+1, values[i]);
}
printf("%s\n", failsafe_state?"FAIL":"OK");
#endif
}
}
}
#endif
#ifdef TEST_HEX_PROGRAM
/*
test harness for use under Linux with hex dump in a file
*/
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <time.h>
#include <unistd.h>
#include <stdlib.h>
#include <termios.h>
int main(int argc, const char *argv[])
{
FILE *f = fopen(argv[1], "r");
if (!f) {
perror(argv[1]);
exit(1);
}
uint64_t t=0;
while (true) {
uint8_t b;
uint8_t num_values = 0;
uint16_t values[20];
bool failsafe_state;
unsigned u[18];
if (fscanf(f, "%02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x",
&u[0], &u[1], &u[2], &u[3], &u[4], &u[5], &u[6], &u[7], &u[8], &u[9],
&u[10], &u[11], &u[12], &u[13], &u[14], &u[15], &u[16], &u[17]) != 18) {
break;
}
t += 11000;
for (uint8_t i=0; i<18; i++) {
b = u[i];
if (srxl_decode(t, b, &num_values, values, sizeof(values)/sizeof(values[0]), &failsafe_state) == 0) {
#if 1
printf("%u: ", num_values);
for (uint8_t i=0; i<num_values; i++) {
printf("%u:%4u ", i+1, values[i]);
}
printf("%s\n", failsafe_state?"FAIL":"OK");
#endif
}
}
}
}
#endif