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ardupilot/libraries/AP_HAL/utility/dsm.cpp

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/*
DSM decoder, based on src/modules/px4iofirmware/dsm.c from PX4Firmware
modified for use in AP_HAL_* by Andrew Tridgell
*/
/****************************************************************************
*
* Copyright (c) 2012-2014 PX4 Development Team. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name PX4 nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
#include <stdint.h>
#include <stdio.h>
#include "dsm.h"
#define DSM_FRAME_SIZE 16 /**<DSM frame size in bytes*/
#define DSM_FRAME_CHANNELS 7 /**<Max supported DSM channels*/
static uint64_t dsm_last_frame_time; /**< Timestamp for start of last dsm frame */
static unsigned dsm_channel_shift; /**< Channel resolution, 0=unknown, 10=10 bit, 11=11 bit */
//#define DEBUG
#ifdef DEBUG
# define debug(fmt, args...) printf(fmt "\n", ##args)
#else
# define debug(fmt, args...) do {} while(0)
#endif
/**
* Attempt to decode a single channel raw channel datum
*
* The DSM* protocol doesn't provide any explicit framing,
* so we detect dsm frame boundaries by the inter-dsm frame delay.
*
* The minimum dsm frame spacing is 11ms; with 16 bytes at 115200bps
* dsm frame transmission time is ~1.4ms.
*
* We expect to only be called when bytes arrive for processing,
* and if an interval of more than 5ms passes between calls,
* the first byte we read will be the first byte of a dsm frame.
*
* In the case where byte(s) are dropped from a dsm frame, this also
* provides a degree of protection. Of course, it would be better
* if we didn't drop bytes...
*
* Upon receiving a full dsm frame we attempt to decode it
*
* @param[in] raw 16 bit raw channel value from dsm frame
* @param[in] shift position of channel number in raw data
* @param[out] channel pointer to returned channel number
* @param[out] value pointer to returned channel value
* @return true=raw value successfully decoded
*/
static bool
dsm_decode_channel(uint16_t raw, unsigned shift, unsigned *channel, unsigned *value)
{
if (raw == 0xffff)
return false;
*channel = (raw >> shift) & 0xf;
uint16_t data_mask = (1 << shift) - 1;
*value = raw & data_mask;
//debug("DSM: %d 0x%04x -> %d %d", shift, raw, *channel, *value);
return true;
}
/**
* Attempt to guess if receiving 10 or 11 bit channel values
*
* @param[in] reset true=reset the 10/11 bit state to unknown
*/
static void
dsm_guess_format(bool reset, const uint8_t dsm_frame[16])
{
static uint32_t cs10;
static uint32_t cs11;
static unsigned samples;
/* reset the 10/11 bit sniffed channel masks */
if (reset) {
cs10 = 0;
cs11 = 0;
samples = 0;
dsm_channel_shift = 0;
return;
}
/* scan the channels in the current dsm_frame in both 10- and 11-bit mode */
for (unsigned i = 0; i < DSM_FRAME_CHANNELS; i++) {
const uint8_t *dp = &dsm_frame[2 + (2 * i)];
uint16_t raw = (dp[0] << 8) | dp[1];
unsigned channel, value;
/* if the channel decodes, remember the assigned number */
if (dsm_decode_channel(raw, 10, &channel, &value) && (channel < 31))
cs10 |= (1 << channel);
if (dsm_decode_channel(raw, 11, &channel, &value) && (channel < 31))
cs11 |= (1 << channel);
/* XXX if we cared, we could look for the phase bit here to decide 1 vs. 2-dsm_frame format */
}
/* wait until we have seen plenty of frames - 5 should normally be enough */
if (samples++ < 5)
return;
/*
* Iterate the set of sensible sniffed channel sets and see whether
* decoding in 10 or 11-bit mode has yielded anything we recognize.
*
* XXX Note that due to what seem to be bugs in the DSM2 high-resolution
* stream, we may want to sniff for longer in some cases when we think we
* are talking to a DSM2 receiver in high-resolution mode (so that we can
* reject it, ideally).
* See e.g. http://git.openpilot.org/cru/OPReview-116 for a discussion
* of this issue.
*/
static uint32_t masks[] = {
0x3f, /* 6 channels (DX6) */
0x7f, /* 7 channels (DX7) */
0xff, /* 8 channels (DX8) */
0x1ff, /* 9 channels (DX9, etc.) */
0x3ff, /* 10 channels (DX10) */
0x1fff, /* 13 channels (DX10t) */
0x3fff /* 18 channels (DX10) */
};
unsigned votes10 = 0;
unsigned votes11 = 0;
for (unsigned i = 0; i < sizeof(masks)/sizeof(masks[0]); i++) {
if (cs10 == masks[i])
votes10++;
if (cs11 == masks[i])
votes11++;
}
if ((votes11 == 1) && (votes10 == 0)) {
dsm_channel_shift = 11;
debug("DSM: 11-bit format");
return;
}
if ((votes10 == 1) && (votes11 == 0)) {
dsm_channel_shift = 10;
debug("DSM: 10-bit format");
return;
}
/* call ourselves to reset our state ... we have to try again */
debug("DSM: format detect fail, 10: 0x%08x %u 11: 0x%08x %u", cs10, votes10, cs11, votes11);
dsm_guess_format(true, dsm_frame);
}
/**
* Decode the entire dsm frame (all contained channels)
*
*/
bool
dsm_decode(uint64_t frame_time, const uint8_t dsm_frame[16], uint16_t *values, uint16_t *num_values, uint16_t max_values)
{
/*
debug("DSM dsm_frame %02x%02x %02x%02x %02x%02x %02x%02x %02x%02x %02x%02x %02x%02x %02x%02x",
dsm_frame[0], dsm_frame[1], dsm_frame[2], dsm_frame[3], dsm_frame[4], dsm_frame[5], dsm_frame[6], dsm_frame[7],
dsm_frame[8], dsm_frame[9], dsm_frame[10], dsm_frame[11], dsm_frame[12], dsm_frame[13], dsm_frame[14], dsm_frame[15]);
*/
/*
* If we have lost signal for at least a second, reset the
* format guessing heuristic.
*/
if (((frame_time - dsm_last_frame_time) > 1000000) && (dsm_channel_shift != 0))
dsm_guess_format(true, dsm_frame);
/* we have received something we think is a dsm_frame */
dsm_last_frame_time = frame_time;
/* if we don't know the dsm_frame format, update the guessing state machine */
if (dsm_channel_shift == 0) {
dsm_guess_format(false, dsm_frame);
return false;
}
/*
* The encoding of the first two bytes is uncertain, so we're
* going to ignore them for now.
*
* Each channel is a 16-bit unsigned value containing either a 10-
* or 11-bit channel value and a 4-bit channel number, shifted
* either 10 or 11 bits. The MSB may also be set to indicate the
* second dsm_frame in variants of the protocol where more than
* seven channels are being transmitted.
*/
for (unsigned i = 0; i < DSM_FRAME_CHANNELS; i++) {
const uint8_t *dp = &dsm_frame[2 + (2 * i)];
uint16_t raw = (dp[0] << 8) | dp[1];
unsigned channel, value;
if (!dsm_decode_channel(raw, dsm_channel_shift, &channel, &value))
continue;
/* ignore channels out of range */
if (channel >= max_values)
continue;
/* update the decoded channel count */
if (channel >= *num_values)
*num_values = channel + 1;
/* convert 0-1024 / 0-2048 values to 1000-2000 ppm encoding. */
if (dsm_channel_shift == 10)
value *= 2;
/*
* Spektrum scaling is special. There are these basic considerations
*
* * Midpoint is 1520 us
* * 100% travel channels are +- 400 us
*
* We obey the original Spektrum scaling (so a default setup will scale from
* 1100 - 1900 us), but we do not obey the weird 1520 us center point
* and instead (correctly) center the center around 1500 us. This is in order
* to get something useful without requiring the user to calibrate on a digital
* link for no reason.
*/
/* scaled integer for decent accuracy while staying efficient */
value = ((((int)value - 1024) * 1000) / 1700) + 1500;
/*
* Store the decoded channel into the R/C input buffer, taking into
* account the different ideas about channel assignement that we have.
*
* Specifically, the first four channels in rc_channel_data are roll, pitch, thrust, yaw,
* but the first four channels from the DSM receiver are thrust, roll, pitch, yaw.
*/
switch (channel) {
case 0:
channel = 2;
break;
case 1:
channel = 0;
break;
case 2:
channel = 1;
break;
default:
break;
}
values[channel] = value;
}
/*
* Spektrum likes to send junk in higher channel numbers to fill
* their packets. We don't know about a 13 channel model in their TX
* lines, so if we get a channel count of 13, we'll return 12 (the last
* data index that is stable).
*/
if (*num_values == 13)
*num_values = 12;
#if 0
if (dsm_channel_shift == 11) {
/* Set the 11-bit data indicator */
*num_values |= 0x8000;
}
#endif
/*
* XXX Note that we may be in failsafe here; we need to work out how to detect that.
*/
return true;
}
#if defined(TEST_MAIN_PROGRAM) || defined(TEST_HEX_STRING)
static uint8_t dsm_partial_frame_count;
static uint8_t dsm_frame[DSM_FRAME_SIZE];
static enum DSM_DECODE_STATE {
DSM_DECODE_STATE_DESYNC = 0,
DSM_DECODE_STATE_SYNC
} dsm_decode_state = DSM_DECODE_STATE_DESYNC;
static uint64_t dsm_last_rx_time; /**< Timestamp when we last received data */
static uint16_t dsm_chan_count;
static uint16_t dsm_frame_drops;
static bool
dsm_parse(uint64_t now, uint8_t *frame, unsigned len, uint16_t *values,
uint16_t *num_values, bool *dsm_11_bit, unsigned *frame_drops, uint16_t max_channels)
{
/* this is set by the decoding state machine and will default to false
* once everything that was decodable has been decoded.
*/
bool decode_ret = false;
/* keep decoding until we have consumed the buffer */
for (unsigned d = 0; d < len; d++) {
/* overflow check */
if (dsm_partial_frame_count == sizeof(dsm_frame) / sizeof(dsm_frame[0])) {
dsm_partial_frame_count = 0;
dsm_decode_state = DSM_DECODE_STATE_DESYNC;
#ifdef DSM_DEBUG
printf("DSM: RESET (BUF LIM)\n");
#endif
}
if (dsm_partial_frame_count == DSM_FRAME_SIZE) {
dsm_partial_frame_count = 0;
dsm_decode_state = DSM_DECODE_STATE_DESYNC;
#ifdef DSM_DEBUG
printf("DSM: RESET (PACKET LIM)\n");
#endif
}
#ifdef DSM_DEBUG
#if 1
printf("dsm state: %s%s, count: %d, val: %02x\n",
(dsm_decode_state == DSM_DECODE_STATE_DESYNC) ? "DSM_DECODE_STATE_DESYNC" : "",
(dsm_decode_state == DSM_DECODE_STATE_SYNC) ? "DSM_DECODE_STATE_SYNC" : "",
dsm_partial_frame_count,
(unsigned)frame[d]);
#endif
#endif
switch (dsm_decode_state) {
case DSM_DECODE_STATE_DESYNC:
/* we are de-synced and only interested in the frame marker */
if ((now - dsm_last_rx_time) > 5000) {
printf("resync %u\n", dsm_partial_frame_count);
dsm_decode_state = DSM_DECODE_STATE_SYNC;
dsm_partial_frame_count = 0;
dsm_chan_count = 0;
dsm_frame[dsm_partial_frame_count++] = frame[d];
}
break;
case DSM_DECODE_STATE_SYNC: {
dsm_frame[dsm_partial_frame_count++] = frame[d];
/* decode whatever we got and expect */
if (dsm_partial_frame_count < DSM_FRAME_SIZE) {
break;
}
/*
* Great, it looks like we might have a frame. Go ahead and
* decode it.
*/
decode_ret = dsm_decode(now, dsm_frame, values, &dsm_chan_count, max_channels);
#if 1
printf("%u %u: ", ((unsigned)(now/1000)) % 1000000, len);
for (uint8_t i=0; i<DSM_FRAME_SIZE; i++) {
printf("%02x ", (unsigned)dsm_frame[i]);
}
printf("\n");
#endif
/* we consumed the partial frame, reset */
dsm_partial_frame_count = 0;
/* if decoding failed, set proto to desync */
if (decode_ret == false) {
dsm_decode_state = DSM_DECODE_STATE_DESYNC;
dsm_frame_drops++;
printf("drop ");
for (uint8_t i=0; i<DSM_FRAME_SIZE; i++) {
printf("%02x ", (unsigned)dsm_frame[i]);
}
printf("\n");
}
}
break;
default:
#ifdef DSM_DEBUG
printf("UNKNOWN PROTO STATE");
#endif
decode_ret = false;
}
}
if (frame_drops) {
*frame_drops = dsm_frame_drops;
}
if (decode_ret) {
*num_values = dsm_chan_count;
}
dsm_last_rx_time = now;
/* return false as default */
return decode_ret;
}
#endif
#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>
#include <string.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|O_CLOEXEC);
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);
uint16_t values[18];
memset(values, 0, sizeof(values));
while (true) {
uint8_t b[16];
uint16_t num_values = 0;
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, nullptr, nullptr, &tv) != 1) {
break;
}
ssize_t nread;
if ((nread = read(fd, b, sizeof(b))) < 1) {
break;
}
bool dsm_11_bit;
unsigned frame_drops;
if (dsm_parse(micros64(), b, nread, values, &num_values, &dsm_11_bit, &frame_drops, 18)) {
#if 1
printf("%u: ", num_values);
for (uint8_t i=0; i<num_values; i++) {
printf("%u:%4u ", i+1, values[i]);
}
printf("\n");
#endif
}
}
}
#elif defined(TEST_HEX_STRING)
/*
test harness providing hex string to decode
*/
#include <string.h>
int main(int argc, const char *argv[])
{
uint8_t b[16];
uint64_t t = 0;
for (uint8_t i=1; i<argc; i++) {
unsigned v;
if (sscanf(argv[i], "%02x", &v) != 1 || v > 255) {
printf("Bad hex value at %u : %s\n", (unsigned)i, argv[i]);
return 1;
}
b[i-1] = v;
}
uint16_t values[18];
memset(values, 0, sizeof(values));
while (true) {
uint16_t num_values = 0;
bool dsm_11_bit;
unsigned frame_drops;
t += 11000;
if (dsm_parse(t, b, sizeof(b), values, &num_values, &dsm_11_bit, &frame_drops, 18)) {
#if 1
printf("%u: ", num_values);
for (uint8_t i=0; i<num_values; i++) {
printf("%u:%4u ", i+1, values[i]);
}
printf("\n");
#endif
}
}
}
#endif
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