ardupilot/ArduPlane/failsafe.pde

// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
/*
 *  failsafe support
 *  Andrew Tridgell, December 2011
 */

/*
 *  our failsafe strategy is to detect main loop lockup and switch to
 *  passing inputs straight from the RC inputs to RC outputs.
 */

/*
 *  this failsafe_check function is called from the core timer interrupt
 *  at 1kHz.
 */
void failsafe_check(void)
{
    static uint16_t last_mainLoop_count;
    static uint32_t last_timestamp;
    static bool in_failsafe;
    uint32_t tnow = hal.scheduler->micros();

    if (mainLoop_count != last_mainLoop_count) {
        // the main loop is running, all is OK
        last_mainLoop_count = mainLoop_count;
        last_timestamp = tnow;
        in_failsafe = false;
        return;
    }

    if (tnow - last_timestamp > 200000) {
        // we have gone at least 0.2 seconds since the main loop
        // ran. That means we're in trouble, or perhaps are in
        // an initialisation routine or log erase. Start passing RC
        // inputs through to outputs
        in_failsafe = true;
    }

    if (in_failsafe && tnow - last_timestamp > 20000) {
        // pass RC inputs to outputs every 20ms
        last_timestamp = tnow;
        hal.rcin->clear_overrides();
        channel_roll->radio_out     = channel_roll->read();
        channel_pitch->radio_out    = channel_pitch->read();
        channel_throttle->radio_out = channel_throttle->read();
        channel_rudder->radio_out   = channel_rudder->read();

        // setup secondary output channels that don't have
        // corresponding input channels
        RC_Channel_aux::set_servo_out(RC_Channel_aux::k_aileron, channel_roll->radio_out);
        RC_Channel_aux::set_servo_out(RC_Channel_aux::k_elevator, channel_pitch->radio_out);
        RC_Channel_aux::set_servo_out(RC_Channel_aux::k_rudder, channel_rudder->radio_out);
        RC_Channel_aux::set_servo_out(RC_Channel_aux::k_steering, channel_rudder->radio_out);

        if (g.vtail_output != MIXING_DISABLED) {
            channel_output_mixer(g.vtail_output, channel_pitch->radio_out, channel_rudder->radio_out);
        } else if (g.elevon_output != MIXING_DISABLED) {
            channel_output_mixer(g.elevon_output, channel_pitch->radio_out, channel_roll->radio_out);
        }

#if OBC_FAILSAFE == ENABLED
        // this is to allow the failsafe module to deliberately crash 
        // the plane. Only used in extreme circumstances to meet the
        // OBC rules
        obc.check_crash_plane();
#endif

        if (!demoing_servos) {
            channel_roll->output();
        }
        channel_pitch->output();
        channel_throttle->output();
        channel_rudder->output();

        // setup secondary output channels that do have
        // corresponding input channels
        RC_Channel_aux::copy_radio_in_out(RC_Channel_aux::k_manual, true);
        RC_Channel_aux::copy_radio_in_out(RC_Channel_aux::k_aileron_with_input, true);
        RC_Channel_aux::copy_radio_in_out(RC_Channel_aux::k_elevator_with_input, true);
        RC_Channel_aux::set_servo_out(RC_Channel_aux::k_flap, 0);
        RC_Channel_aux::set_servo_out(RC_Channel_aux::k_flap_auto, 0);

        // setup flaperons
        flaperon_update(0);
    }
}