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ardupilot/libraries/AP_RCProtocol/AP_RCProtocol_GHST.cpp

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/*
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/>.
*/
/*
GHST protocol decoder based on betaflight implementation
Code by Andy Piper
*/
#include "AP_RCProtocol_config.h"
#if AP_RCPROTOCOL_GHST_ENABLED
#define CRSF_BAUDRATE 416666U
#include "AP_RCProtocol.h"
#include "AP_RCProtocol_GHST.h"
#include <AP_HAL/AP_HAL.h>
#include <AP_Math/AP_Math.h>
#include <AP_Math/crc.h>
#include <AP_Vehicle/AP_Vehicle_Type.h>
#include <AP_RCTelemetry/AP_GHST_Telem.h>
#include <AP_SerialManager/AP_SerialManager.h>
/*
* GHST protocol
*
* GHST protocol uses a single wire half duplex uart connection.
*
* 420000 baud
* not inverted
* 8 Bit
* 1 Stop bit
* Big endian
* Max frame size is 14 bytes
*
* Every frame has the structure:
* <Device address><Frame length><Type><Payload><CRC>
*
* Device address: (uint8_t)
* Frame length: length in bytes including Type (uint8_t)
* Type: (uint8_t)
* CRC: (uint8_t)
*
*/
extern const AP_HAL::HAL& hal;
//#define GHST_DEBUG
//#define GHST_DEBUG_CHARS
#ifdef GHST_DEBUG
# define debug(fmt, args...) hal.console->printf("GHST: " fmt "\n", ##args)
static const char* get_frame_type(uint8_t byte, uint8_t subtype = 0)
{
switch(byte) {
case AP_RCProtocol_GHST::GHST_UL_RC_CHANS_HS4_5TO8:
case AP_RCProtocol_GHST::GHST_UL_RC_CHANS_HS4_12_5TO8:
return "RC5_8";
case AP_RCProtocol_GHST::GHST_UL_RC_CHANS_HS4_9TO12:
case AP_RCProtocol_GHST::GHST_UL_RC_CHANS_HS4_12_9TO12:
return "RC9_12";
case AP_RCProtocol_GHST::GHST_UL_RC_CHANS_HS4_13TO16:
case AP_RCProtocol_GHST::GHST_UL_RC_CHANS_HS4_12_13TO16:
return "RC13_16";
case AP_RCProtocol_GHST::GHST_UL_RC_CHANS_RSSI:
case AP_RCProtocol_GHST::GHST_UL_RC_CHANS_12_RSSI:
return "RSSI";
case AP_RCProtocol_GHST::GHST_UL_RC_VTX_CTRL:
return "VTX_CTRL";
case AP_RCProtocol_GHST::GHST_UL_VTX_SETUP:
return "VTX_SETUP";
}
return "UNKNOWN";
}
#else
# define debug(fmt, args...) do {} while(0)
#endif
#define GHST_MAX_FRAME_TIME_US 500U // 14 bytes @ 420k = ~450us
#define GHST_FRAME_TIMEOUT_US 10000U // 10ms to account for scheduling delays
#define GHST_INTER_FRAME_TIME_US 2000U // At fastest, frames are sent by the transmitter every 2 ms, 500 Hz
#define GHST_HEADER_TYPE_LEN (GHST_HEADER_LEN + 1) // header length including type
const uint16_t AP_RCProtocol_GHST::RF_MODE_RATES[RFMode::RF_MODE_MAX_MODES] = {
55, 160, 250, 19, 250, 500, 150, 250,
};
AP_RCProtocol_GHST* AP_RCProtocol_GHST::_singleton;
AP_RCProtocol_GHST::AP_RCProtocol_GHST(AP_RCProtocol &_frontend) : AP_RCProtocol_Backend(_frontend)
{
#if !APM_BUILD_TYPE(APM_BUILD_UNKNOWN)
if (_singleton != nullptr) {
AP_HAL::panic("Duplicate GHST handler");
}
_singleton = this;
#else
if (_singleton == nullptr) {
_singleton = this;
}
#endif
}
AP_RCProtocol_GHST::~AP_RCProtocol_GHST() {
_singleton = nullptr;
}
// get the protocol string
const char* AP_RCProtocol_GHST::get_protocol_string() const {
return "GHST";
}
// return the link rate as defined by the LinkStatistics
uint16_t AP_RCProtocol_GHST::get_link_rate() const {
return RF_MODE_RATES[_link_status.rf_mode - GHST_RF_MODE_NORMAL];
}
void AP_RCProtocol_GHST::_process_byte(uint32_t timestamp_us, uint8_t byte)
{
//debug("process_byte(0x%x)", byte);
// we took too long decoding, start again - the RX will only send complete frames so this is unlikely to fail,
// however thread scheduling can introduce longer delays even when the data has been received
if (_frame_ofs > 0 && (timestamp_us - _start_frame_time_us) > GHST_FRAME_TIMEOUT_US) {
_frame_ofs = 0;
}
// overflow check
if (_frame_ofs >= GHST_FRAMELEN_MAX) {
_frame_ofs = 0;
}
// start of a new frame
if (_frame_ofs == 0) {
_start_frame_time_us = timestamp_us;
}
add_to_buffer(_frame_ofs++, byte);
// need a header to get the length
if (_frame_ofs < GHST_HEADER_TYPE_LEN) {
return;
}
if (_frame.device_address != DeviceAddress::GHST_ADDRESS_FLIGHT_CONTROLLER) {
return;
}
// parse the length
if (_frame_ofs == GHST_HEADER_TYPE_LEN) {
_frame_crc = crc8_dvb_s2(0, _frame.type);
// check for garbage frame
if (_frame.length > GHST_FRAME_PAYLOAD_MAX) {
_frame_ofs = 0;
}
return;
}
// update crc
if (_frame_ofs < _frame.length + GHST_HEADER_LEN) {
_frame_crc = crc8_dvb_s2(_frame_crc, byte);
}
// overflow check
if (_frame_ofs > _frame.length + GHST_HEADER_LEN) {
_frame_ofs = 0;
return;
}
if (_frame.length < 2) {
// invalid length, we subtract 2 below
_frame_ofs = 0;
return;
}
// decode whatever we got and expect
if (_frame_ofs == _frame.length + GHST_HEADER_LEN) {
log_data(AP_RCProtocol::GHST, timestamp_us, (const uint8_t*)&_frame, _frame_ofs - GHST_HEADER_LEN);
// we consumed the partial frame, reset
_frame_ofs = 0;
// bad CRC (payload start is +1 from frame start, so need to subtract that from frame length to get index)
if (_frame_crc != _frame.payload[_frame.length - 2]) {
return;
}
_last_frame_time_us = _last_rx_frame_time_us = timestamp_us;
// decode here
if (decode_ghost_packet()) {
_last_tx_frame_time_us = timestamp_us; // we have received a frame from the transmitter
add_input(MAX_CHANNELS, _channels, false, _link_status.rssi, _link_status.link_quality);
}
}
}
void AP_RCProtocol_GHST::update(void)
{
}
// write out a frame of any type
bool AP_RCProtocol_GHST::write_frame(Frame* frame)
{
AP_HAL::UARTDriver *uart = get_current_UART();
if (!uart) {
return false;
}
// check that we haven't been too slow in responding to the new UART data. If we respond too late then we will
// corrupt the next incoming control frame. incoming packets at max 126bits @500Hz @420k baud gives total budget of 2ms
// per packet of which we need 300us to receive a packet. outgoing packets are 126bits which require 300us to send
// leaving at most 1.4ms of delay that can be tolerated
uint64_t tend = uart->receive_time_constraint_us(1);
uint64_t now = AP_HAL::micros64();
uint64_t tdelay = now - tend;
if (tdelay > 1000) {
// we've been too slow in responding
return false;
}
// calculate crc
uint8_t crc = crc8_dvb_s2(0, frame->type);
for (uint8_t i = 0; i < frame->length - 2; i++) {
crc = crc8_dvb_s2(crc, frame->payload[i]);
}
frame->payload[frame->length - 2] = crc;
uart->write((uint8_t*)frame, frame->length + 2);
uart->flush();
#ifdef GHST_DEBUG
hal.console->printf("GHST: writing %s:", get_frame_type(frame->type, frame->payload[0]));
for (uint8_t i = 0; i < frame->length + 2; i++) {
uint8_t val = ((uint8_t*)frame)[i];
#ifdef GHST_DEBUG_CHARS
if (val >= 32 && val <= 126) {
hal.console->printf(" 0x%x '%c'", val, (char)val);
} else {
#endif
hal.console->printf(" 0x%x", val);
#ifdef GHST_DEBUG_CHARS
}
#endif
}
hal.console->printf("\n");
#endif
return true;
}
bool AP_RCProtocol_GHST::decode_ghost_packet()
{
#ifdef GHST_DEBUG
hal.console->printf("GHST: received %s:", get_frame_type(_frame.type));
uint8_t* fptr = (uint8_t*)&_frame;
for (uint8_t i = 0; i < _frame.length + 2; i++) {
#ifdef GHST_DEBUG_CHARS
if (fptr[i] >= 32 && fptr[i] <= 126) {
hal.console->printf(" 0x%x '%c'", fptr[i], (char)fptr[i]);
} else {
#endif
hal.console->printf(" 0x%x", fptr[i]);
#ifdef GHST_DEBUG_CHARS
}
#endif
}
hal.console->printf("\n");
#endif
const RadioFrame* radio_frame = (const RadioFrame*)(&_frame.payload);
const Channels12Bit_4Chan* channels = &(radio_frame->channels);
const uint8_t* lowres_channels = radio_frame->lowres_channels;
// Scaling from Betaflight
// Scaling 12bit channels (8bit channels in brackets)
// OpenTx RC PWM (BF)
// min -1024 0( 0) 988us
// ctr 0 2048(128) 1500us
// max 1024 4096(256) 2012us
//
// Scaling legacy (nearly 10bit)
// derived from original SBus scaling, with slight correction for offset
// now symmetrical around OpenTx 0 value
// scaling is:
// OpenTx RC PWM (BF)
// min -1024 172( 22) 988us
// ctr 0 992(124) 1500us
// max 1024 1811(226) 2012us
#define CHANNEL_RESCALE(x) (((5 * x) >> 2) - 430)
#define CHANNEL_SCALE(x) (int32_t(x) / 4 + 988)
#define CHANNEL_SCALE_LEGACY(x) CHANNEL_SCALE(CHANNEL_RESCALE(x))
// legacy scaling
if (_frame.type >= GHST_UL_RC_CHANS_HS4_5TO8 && _frame.type <= GHST_UL_RC_CHANS_RSSI) {
_channels[0] = CHANNEL_SCALE_LEGACY(channels->ch0);
_channels[1] = CHANNEL_SCALE_LEGACY(channels->ch1);
_channels[2] = CHANNEL_SCALE_LEGACY(channels->ch2);
_channels[3] = CHANNEL_SCALE_LEGACY(channels->ch3);
} else {
_channels[0] = CHANNEL_SCALE(channels->ch0);
_channels[1] = CHANNEL_SCALE(channels->ch1);
_channels[2] = CHANNEL_SCALE(channels->ch2);
_channels[3] = CHANNEL_SCALE(channels->ch3);
}
#define CHANNEL_LR_RESCALE(x) (5 * x - 108)
#define CHANNEL_LR_SCALE(x) (int32_t(x) * 2 + 988)
#define CHANNEL_LR_SCALE_LEGACY(x) (CHANNEL_LR_RESCALE(x) + 988)
switch (_frame.type) {
case GHST_UL_RC_CHANS_HS4_5TO8:
case GHST_UL_RC_CHANS_HS4_9TO12:
case GHST_UL_RC_CHANS_HS4_13TO16: {
uint8_t offset = (_frame.type - GHST_UL_RC_CHANS_HS4_5TO8 + 1) * 4;
_channels[offset++] = CHANNEL_LR_SCALE_LEGACY(lowres_channels[0]);
_channels[offset++] = CHANNEL_LR_SCALE_LEGACY(lowres_channels[1]);
_channels[offset++] = CHANNEL_LR_SCALE_LEGACY(lowres_channels[2]);
_channels[offset++] = CHANNEL_LR_SCALE_LEGACY(lowres_channels[3]);
break;
}
case GHST_UL_RC_CHANS_HS4_12_5TO8:
case GHST_UL_RC_CHANS_HS4_12_9TO12:
case GHST_UL_RC_CHANS_HS4_12_13TO16: {
uint8_t offset = (_frame.type - GHST_UL_RC_CHANS_HS4_12_5TO8 + 1) * 4;
_channels[offset++] = CHANNEL_LR_SCALE(lowres_channels[0]);
_channels[offset++] = CHANNEL_LR_SCALE(lowres_channels[1]);
_channels[offset++] = CHANNEL_LR_SCALE(lowres_channels[2]);
_channels[offset++] = CHANNEL_LR_SCALE(lowres_channels[3]);
break;
}
case GHST_UL_RC_CHANS_RSSI:
case GHST_UL_RC_CHANS_12_RSSI:
process_link_stats_frame((uint8_t*)&_frame.payload);
break;
default:
break;
}
#if AP_GHST_TELEM_ENABLED
if (AP_GHST_Telem::process_frame(FrameType(_frame.type), (uint8_t*)&_frame.payload)) {
process_telemetry();
}
#endif
return true;
}
// send out telemetry
bool AP_RCProtocol_GHST::process_telemetry(bool check_constraint)
{
AP_HAL::UARTDriver *uart = get_current_UART();
if (!uart) {
return false;
}
if (!telem_available) {
#if AP_GHST_TELEM_ENABLED
if (AP_GHST_Telem::get_telem_data(&_telemetry_frame, is_tx_active())) {
telem_available = true;
} else {
return false;
}
#else
return false;
#endif
}
if (!write_frame(&_telemetry_frame)) {
return false;
}
// get fresh telem_data in the next call
telem_available = false;
return true;
}
// process link statistics to get RSSI
void AP_RCProtocol_GHST::process_link_stats_frame(const void* data)
{
const LinkStatisticsFrame* link = (const LinkStatisticsFrame*)data;
uint8_t rssi_dbm;
rssi_dbm = link->rssi_dbm;
_link_status.link_quality = link->link_quality;
if (_use_lq_for_rssi) {
_link_status.rssi = derive_scaled_lq_value(link->link_quality);
} else{
// AP rssi: -1 for unknown, 0 for no link, 255 for maximum link
if (rssi_dbm < 50) {
_link_status.rssi = 255;
} else if (rssi_dbm > 120) {
_link_status.rssi = 0;
} else {
// this is an approximation recommended by Remo from TBS
_link_status.rssi = int16_t(roundf((1.0f - (rssi_dbm - 50.0f) / 70.0f) * 255.0f));
}
}
_link_status.rf_mode = link->protocol;
}
bool AP_RCProtocol_GHST::is_telemetry_supported() const
{
return _link_status.rf_mode == AP_RCProtocol_GHST::GHST_RF_MODE_NORMAL
|| _link_status.rf_mode == AP_RCProtocol_GHST::GHST_RF_MODE_RACE
|| _link_status.rf_mode == AP_RCProtocol_GHST::GHST_RF_MODE_LR
|| _link_status.rf_mode == AP_RCProtocol_GHST::GHST_RF_MODE_RACE250;
}
// process a byte provided by a uart
void AP_RCProtocol_GHST::process_byte(uint8_t byte, uint32_t baudrate)
{
// reject RC data if we have been configured for standalone mode
if (baudrate != CRSF_BAUDRATE && baudrate != GHST_BAUDRATE) {
return;
}
_process_byte(AP_HAL::micros(), byte);
}
// change the bootstrap baud rate to Ghost standard if configured
void AP_RCProtocol_GHST::process_handshake(uint32_t baudrate)
{
AP_HAL::UARTDriver *uart = get_current_UART();
// only change the baudrate if we are specifically bootstrapping Ghost
if (uart == nullptr
|| baudrate != CRSF_BAUDRATE
|| baudrate == GHST_BAUDRATE
|| uart->get_baud_rate() == GHST_BAUDRATE
|| !protocol_enabled(AP_RCProtocol::GHST)) {
return;
}
#if AP_RCPROTOCOL_CRSF_ENABLED
if (protocol_enabled(AP_RCProtocol::CRSF)) {
// don't fight CRSF
return;
}
#endif
uart->begin(GHST_BAUDRATE);
}
//returns uplink link quality on 0-255 scale
int16_t AP_RCProtocol_GHST::derive_scaled_lq_value(uint8_t uplink_lq)
{
return int16_t(roundf(constrain_float(uplink_lq*2.5f,0,255)));
}
namespace AP {
AP_RCProtocol_GHST* ghost() {
return AP_RCProtocol_GHST::get_singleton();
}
};
#endif // AP_RCPROTOCOL_GHST_ENABLED
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