ardupilot/libraries/AP_RCProtocol/AP_RCProtocol_IBUS.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/>.
*
*/
#include "AP_RCProtocol_IBUS.h"
// constructor
AP_RCProtocol_IBUS::AP_RCProtocol_IBUS(AP_RCProtocol &_frontend) :
AP_RCProtocol_Backend(_frontend)
{}
// decode a full IBUS frame
bool AP_RCProtocol_IBUS::ibus_decode(const uint8_t frame[IBUS_FRAME_SIZE], uint16_t *values, bool *ibus_failsafe)
{
uint32_t chksum = 96;
/* check frame boundary markers to avoid out-of-sync cases */
if ((frame[0] != 0x20) || (frame[1] != 0x40)) {
return false;
}
/* use the decoder matrix to extract channel data */
for (uint8_t channel = 0, pick=2; channel < IBUS_INPUT_CHANNELS; channel++, pick+=2) {
values[channel]=frame[pick]|(frame[pick+1] & 0x0F)<<8;
chksum+=frame[pick]+frame[pick+1];
}
chksum += frame[IBUS_FRAME_SIZE-2]|frame[IBUS_FRAME_SIZE-1]<<8;
if (chksum!=0xFFFF) {
return false;
}
if ((frame[3]&0xF0) || (frame[9]&0xF0)) {
*ibus_failsafe = true;
} else {
*ibus_failsafe = false;
}
return true;
}
/*
process an IBUS input pulse of the given width
*/
void AP_RCProtocol_IBUS::process_pulse(uint32_t w0, uint32_t w1)
{
uint8_t b;
if (ss.process_pulse(w0, w1, b)) {
_process_byte(ss.get_byte_timestamp_us(), b);
}
}
// support byte input
void AP_RCProtocol_IBUS::_process_byte(uint32_t timestamp_us, uint8_t b)
{
const bool have_frame_gap = (timestamp_us - byte_input.last_byte_us >= 2000U);
byte_input.last_byte_us = timestamp_us;
if (have_frame_gap) {
// if we have a frame gap then this must be the start of a new
// frame
byte_input.ofs = 0;
}
if (b != 0x20 && byte_input.ofs == 0) {
// definately not IBUS, missing header byte
return;
}
if (byte_input.ofs == 0 && !have_frame_gap) {
// must have a frame gap before the start of a new IBUS frame
return;
}
byte_input.buf[byte_input.ofs++] = b;
if (byte_input.ofs == sizeof(byte_input.buf)) {
uint16_t values[IBUS_INPUT_CHANNELS];
bool ibus_failsafe = false;
if (ibus_decode(byte_input.buf, values, &ibus_failsafe)) {
add_input(IBUS_INPUT_CHANNELS, values, ibus_failsafe);
}
byte_input.ofs = 0;
}
}
// support byte input
void AP_RCProtocol_IBUS::process_byte(uint8_t b, uint32_t baudrate)
{
if (baudrate != 115200) {
return;
}
_process_byte(AP_HAL::micros(), b);
}