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(uint32_t tnow)
{
    static uint16_t last_mainLoop_count;
    static uint32_t last_timestamp;
    static bool in_failsafe;

    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;
        APM_RC.clearOverride();
        for (uint8_t ch=0; ch<8; ch++) {
            APM_RC.OutputCh(ch, APM_RC.InputCh(ch));
        }
    }
}