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ardupilot/libraries/AP_RCProtocol/AP_RCProtocol_DSM.cpp

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/*
* This file 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 file 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/>.
*
* Code by Andrew Tridgell and Siddharth Bharat Purohit
*/
/*
with thanks to PX4 dsm.c for DSM decoding approach
*/
#include "AP_RCProtocol_DSM.h"
extern const AP_HAL::HAL& hal;
// #define DSM_DEBUG
#ifdef DSM_DEBUG
# define debug(fmt, args...) printf(fmt "\n", ##args)
#else
# define debug(fmt, args...) do {} while(0)
#endif
#define DSM_FRAME_SIZE 16 /**<DSM frame size in bytes*/
#define DSM_FRAME_CHANNELS 7 /**<Max supported DSM channels*/
void AP_RCProtocol_DSM::process_pulse(uint32_t width_s0, uint32_t width_s1)
{
uint8_t b;
if (ss.process_pulse(width_s0, width_s1, b)) {
_process_byte(ss.get_byte_timestamp_us()/1000U, b);
}
}
/**
* 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
*/
bool AP_RCProtocol_DSM::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
*/
void AP_RCProtocol_DSM::dsm_guess_format(bool reset, const uint8_t dsm_frame[16])
{
/* reset the 10/11 bit sniffed channel masks */
if (reset) {
cs10 = 0;
cs11 = 0;
samples = 0;
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 const 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)) {
channel_shift = 11;
debug("DSM: 11-bit format");
return;
}
if ((votes10 == 1) && (votes11 == 0)) {
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 AP_RCProtocol_DSM::dsm_decode(uint32_t frame_time_ms, const uint8_t dsm_frame[16],
uint16_t *values, uint16_t *num_values, uint16_t max_values)
{
/*
* If we have lost signal for at least 200ms, reset the
* format guessing heuristic.
*/
if (((frame_time_ms - last_frame_time_ms) > 200U) && (channel_shift != 0)) {
dsm_guess_format(true, dsm_frame);
}
/* we have received something we think is a dsm_frame */
last_frame_time_ms = frame_time_ms;
/* if we don't know the dsm_frame format, update the guessing state machine */
if (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, 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 (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;
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 (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;
}
/*
start bind on DSM satellites
*/
void AP_RCProtocol_DSM::start_bind(void)
{
bind_state = BIND_STATE1;
}
/*
update function used for bind state machine
*/
void AP_RCProtocol_DSM::update(void)
{
#if defined(HAL_GPIO_SPEKTRUM_PWR) && defined(HAL_GPIO_SPEKTRUM_RC)
switch (bind_state) {
case BIND_STATE_NONE:
break;
case BIND_STATE1:
hal.gpio->write(HAL_GPIO_SPEKTRUM_PWR, !HAL_SPEKTRUM_PWR_ENABLED);
hal.gpio->pinMode(HAL_GPIO_SPEKTRUM_RC, 1);
hal.gpio->write(HAL_GPIO_SPEKTRUM_RC, 1);
bind_last_ms = AP_HAL::millis();
bind_state = BIND_STATE2;
break;
case BIND_STATE2: {
uint32_t now = AP_HAL::millis();
if (now - bind_last_ms > 500) {
hal.gpio->write(HAL_GPIO_SPEKTRUM_PWR, HAL_SPEKTRUM_PWR_ENABLED);
bind_last_ms = now;
bind_state = BIND_STATE3;
}
break;
}
case BIND_STATE3: {
uint32_t now = AP_HAL::millis();
if (now - bind_last_ms > 72) {
// 9 pulses works with all satellite receivers, and supports the highest
// available protocol
const uint8_t num_pulses = 9;
for (uint8_t i=0; i<num_pulses; i++) {
hal.scheduler->delay_microseconds(120);
hal.gpio->write(HAL_GPIO_SPEKTRUM_RC, 0);
hal.scheduler->delay_microseconds(120);
hal.gpio->write(HAL_GPIO_SPEKTRUM_RC, 1);
}
bind_last_ms = now;
bind_state = BIND_STATE4;
}
break;
}
case BIND_STATE4: {
uint32_t now = AP_HAL::millis();
if (now - bind_last_ms > 50) {
hal.gpio->pinMode(HAL_GPIO_SPEKTRUM_RC, 0);
bind_state = BIND_STATE_NONE;
}
break;
}
}
#endif
}
/*
parse one DSM byte, maintaining decoder state
*/
bool AP_RCProtocol_DSM::dsm_parse_byte(uint32_t frame_time_ms, uint8_t b, uint16_t *values,
uint16_t *num_values, 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;
/* overflow check */
if (byte_input.ofs == sizeof(byte_input.buf) / sizeof(byte_input.buf[0])) {
byte_input.ofs = 0;
dsm_decode_state = DSM_DECODE_STATE_DESYNC;
debug("DSM: RESET (BUF LIM)\n");
}
if (byte_input.ofs == DSM_FRAME_SIZE) {
byte_input.ofs = 0;
dsm_decode_state = DSM_DECODE_STATE_DESYNC;
debug("DSM: RESET (PACKET LIM)\n");
}
#ifdef DSM_DEBUG
debug("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" : "",
byte_input.ofs,
(unsigned)b);
#endif
switch (dsm_decode_state) {
case DSM_DECODE_STATE_DESYNC:
/* we are de-synced and only interested in the frame marker */
if ((frame_time_ms - last_rx_time_ms) >= 5) {
dsm_decode_state = DSM_DECODE_STATE_SYNC;
byte_input.ofs = 0;
byte_input.buf[byte_input.ofs++] = b;
}
break;
case DSM_DECODE_STATE_SYNC: {
if ((frame_time_ms - last_rx_time_ms) >= 5 && byte_input.ofs > 0) {
byte_input.ofs = 0;
dsm_decode_state = DSM_DECODE_STATE_DESYNC;
break;
}
byte_input.buf[byte_input.ofs++] = b;
/* decode whatever we got and expect */
if (byte_input.ofs < DSM_FRAME_SIZE) {
break;
}
/*
* Great, it looks like we might have a frame. Go ahead and
* decode it.
*/
decode_ret = dsm_decode(frame_time_ms, byte_input.buf, values, &chan_count, max_channels);
/* we consumed the partial frame, reset */
byte_input.ofs = 0;
/* if decoding failed, set proto to desync */
if (decode_ret == false) {
dsm_decode_state = DSM_DECODE_STATE_DESYNC;
}
break;
}
default:
debug("UNKNOWN PROTO STATE");
decode_ret = false;
}
if (decode_ret) {
*num_values = chan_count;
}
last_rx_time_ms = frame_time_ms;
/* return false as default */
return decode_ret;
}
// support byte input
void AP_RCProtocol_DSM::_process_byte(uint32_t timestamp_ms, uint8_t b)
{
uint16_t v[AP_DSM_MAX_CHANNELS];
uint16_t nchan;
memcpy(v, last_values, sizeof(v));
if (dsm_parse_byte(timestamp_ms, b, v, &nchan, AP_DSM_MAX_CHANNELS)) {
memcpy(last_values, v, sizeof(v));
if (nchan >= MIN_RCIN_CHANNELS) {
add_input(nchan, last_values, false);
}
}
}
// support byte input
void AP_RCProtocol_DSM::process_byte(uint8_t b, uint32_t baudrate)
{
if (baudrate != 115200) {
return;
}
_process_byte(AP_HAL::millis(), b);
}
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