ppm.c

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/*
 * Copyright (C) 2010-2014 The Paparazzi Team
 *
 * This file is part of paparazzi.
 *
 * paparazzi 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 2, or (at your option)
 * any later version.
 *
 * paparazzi 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 paparazzi; see the file COPYING.  If not, see
 * <http://www.gnu.org/licenses/>.
 */
 
#include "subsystems/radio_control.h"
#include "subsystems/radio_control/ppm.h"
 
uint16_t ppm_pulses[RADIO_CTL_NB];
volatile bool ppm_frame_available;
 
/*
 * State machine for decoding ppm frames
 */
static uint8_t  ppm_cur_pulse;
static uint32_t ppm_last_pulse_time;
static bool   ppm_data_valid;
 
#ifndef RssiValid
#define RssiValid() TRUE
#endif
 
 
#if PERIODIC_TELEMETRY
#include "subsystems/datalink/telemetry.h"
 
static void send_ppm(struct transport_tx *trans, struct link_device *dev)
{
  uint16_t ppm_pulses_usec[RADIO_CTL_NB];
  for (int i = 0; i < RADIO_CTL_NB; i++) {
    ppm_pulses_usec[i] = USEC_OF_RC_PPM_TICKS(ppm_pulses[i]);
  }
  pprz_msg_send_PPM(trans, dev, AC_ID,
                    &radio_control.frame_rate, RADIO_CTL_NB, ppm_pulses_usec);
}
#endif
 
void radio_control_impl_init(void)
{
  ppm_frame_available = false;
  ppm_last_pulse_time = 0;
  ppm_cur_pulse = RADIO_CTL_NB;
  ppm_data_valid = false;
 
  ppm_arch_init();
 
#if PERIODIC_TELEMETRY
  register_periodic_telemetry(DefaultPeriodic, PPRZ_MSG_ID_PPM, send_ppm);
#endif
}
 
void radio_control_impl_event(void (* _received_frame_handler)(void))
{
  if (ppm_frame_available) {
    radio_control.frame_cpt++;
    radio_control.time_since_last_frame = 0;
    if (radio_control.radio_ok_cpt > 0) {
      radio_control.radio_ok_cpt--;
    } else {
      radio_control.status = RC_OK;
      NormalizePpmIIR(ppm_pulses, radio_control);
      _received_frame_handler();
    }
    ppm_frame_available = false;
  }
}
 
void ppm_decode_frame(uint32_t ppm_time)
{
  uint32_t length = ppm_time - ppm_last_pulse_time;
  ppm_last_pulse_time = ppm_time;
 
  ppm_decode_frame_width(length);
}
 
void ppm_decode_frame_width(uint32_t ppm_width)
{
  if (ppm_cur_pulse == RADIO_CTL_NB) {
    if (ppm_width > RC_PPM_TICKS_OF_USEC(PPM_SYNC_MIN_LEN) &&
        ppm_width < RC_PPM_TICKS_OF_USEC(PPM_SYNC_MAX_LEN)) {
      if (ppm_data_valid && RssiValid()) {
        ppm_frame_available = true;
        ppm_data_valid = false;
      }
      ppm_cur_pulse = 0;
    } else {
      ppm_data_valid = false;
    }
  } else {
    if (ppm_width > RC_PPM_TICKS_OF_USEC(PPM_DATA_MIN_LEN) &&
        ppm_width < RC_PPM_TICKS_OF_USEC(PPM_DATA_MAX_LEN)) {
      ppm_pulses[ppm_cur_pulse] = ppm_width;
      ppm_cur_pulse++;
      if (ppm_cur_pulse == RADIO_CTL_NB) {
        ppm_data_valid = true;
      }
    } else {
      ppm_cur_pulse = RADIO_CTL_NB;
      ppm_data_valid = false;
    }
  }
}