ArduPilot飞行前检查——PreArm解析

ArduPilot飞行前检查 主要包括两个部分:
1. 初始化中遥控器输入检查；
2. 1Hz解锁前检查。
附： 显示地面站信息
参考文章：Ardupilot Pre-Arm安全检查程序分析

1. 初始化中遥控器输入检查

直接跳转进去查看函数为；

bool AP_Arming_Copter::rc_calibration_checks(bool display_failure)
{
    const RC_Channel *channels[] = {
        copter.channel_roll,
        copter.channel_pitch,
        copter.channel_throttle,
        copter.channel_yaw
    };

    copter.ap.pre_arm_rc_check = rc_checks_copter_sub(display_failure, channels)
        & AP_Arming::rc_calibration_checks(display_failure);

    return copter.ap.pre_arm_rc_check;
}

// Copter and sub share the same RC input limits
// Copter checks that min and max have been configured by default, Sub does not
bool AP_Arming::rc_checks_copter_sub(const bool display_failure, const RC_Channel *channels[4]) const
{
    // set rc-checks to success if RC checks are disabled
    if ((checks_to_perform != ARMING_CHECK_ALL) && !(checks_to_perform & ARMING_CHECK_RC)) {
        return true;
    }

    bool ret = true;

    const char *channel_names[] = { "Roll", "Pitch", "Throttle", "Yaw" };

    for (uint8_t i=0; i<ARRAY_SIZE(channel_names);i++) {
        const RC_Channel *channel = channels[i];
        const char *channel_name = channel_names[i];
        // check if radio has been calibrated
        if (channel->get_radio_min() > 1300) {
            check_failed(ARMING_CHECK_RC, display_failure, "%s radio min too high", channel_name);
            ret = false;
        }
        if (channel->get_radio_max() < 1700) {
            check_failed(ARMING_CHECK_RC, display_failure, "%s radio max too low", channel_name);
            ret = false;
        }
        bool fail = true;
        if (i == 2) {
            // skip checking trim for throttle as older code did not check it
            fail = false;
        }
        if (channel->get_radio_trim() < channel->get_radio_min()) {
            check_failed(ARMING_CHECK_RC, display_failure, "%s radio trim below min", channel_name);
            if (fail) {
                ret = false;
            }
        }
        if (channel->get_radio_trim() > channel->get_radio_max()) {
            check_failed(ARMING_CHECK_RC, display_failure, "%s radio trim above max", channel_name);
            if (fail) {
                ret = false;
            }
        }
    }
    return ret;
}

可见里面是对遥控器通道的检查，只有检查通过之后，才允许最后PWM输出。（此时输出为ShutDown状态）

2. 1Hz解锁前检查

// performs pre-arm checks. expects to be called at 1hz.
void AP_Arming_Copter::update(void)
{
    // perform pre-arm checks & display failures every 30 seconds
    static uint8_t pre_arm_display_counter = PREARM_DISPLAY_PERIOD/2;
    pre_arm_display_counter++;
    bool display_fail = false;
    if (pre_arm_display_counter >= PREARM_DISPLAY_PERIOD) {
        display_fail = true;
        pre_arm_display_counter = 0;
    }

    pre_arm_checks(display_fail);
}

执行跳转后为：

bool AP_Arming_Copter::pre_arm_checks(bool display_failure)
{
    const bool passed = run_pre_arm_checks(display_failure);
    set_pre_arm_check(passed);
    return passed;
}

再次跳转查看，得：

bool AP_Arming_Copter::run_pre_arm_checks(bool display_failure)
{
    // exit immediately if already armed
    if (copter.motors->armed()) {
        return true;
    }

    // check if motor interlock and Emergency Stop aux switches are used
    // at the same time.  This cannot be allowed.
    if (rc().find_channel_for_option(RC_Channel::AUX_FUNC::MOTOR_INTERLOCK) &&
        rc().find_channel_for_option(RC_Channel::AUX_FUNC::MOTOR_ESTOP)){
        check_failed(display_failure, "Interlock/E-Stop Conflict");
        return false;
    }

    // check if motor interlock aux switch is in use
    // if it is, switch needs to be in disabled position to arm
    // otherwise exit immediately.  This check to be repeated,
    // as state can change at any time.
    if (copter.ap.using_interlock && copter.ap.motor_interlock_switch) {
        check_failed(display_failure, "Motor Interlock Enabled");
    }

    // if pre arm checks are disabled run only the mandatory checks
    if (checks_to_perform == 0) {
        return mandatory_checks(display_failure);
    }

    return fence_checks(display_failure)
        & parameter_checks(display_failure)
        & motor_checks(display_failure)
        & pilot_throttle_checks(display_failure)
        & oa_checks(display_failure)
        & gcs_failsafe_check(display_failure) &
        AP_Arming::pre_arm_checks(display_failure);
}

同时，在最后一句 AP_Arming::pre_arm_checks(display_failure);中，我们继续深挖，可以看到还有如下检查内容：

bool AP_Arming::pre_arm_checks(bool report)
{
#if !APM_BUILD_TYPE(APM_BUILD_ArduCopter)
    if (armed || require == (uint8_t)Required::NO) {
        // if we are already armed or don't need any arming checks
        // then skip the checks
        return true;
    }
#endif

    return hardware_safety_check(report)
        &  barometer_checks(report)
        &  ins_checks(report)
        &  compass_checks(report)
        &  gps_checks(report)
        &  battery_checks(report)
        &  logging_checks(report)
        &  manual_transmitter_checks(report)
        &  mission_checks(report)
        &  rangefinder_checks(report)
        &  servo_checks(report)
        &  board_voltage_checks(report)
        &  system_checks(report)
        &  can_checks(report)
        &  proximity_checks(report)
        &  camera_checks(report)
        &  aux_auth_checks(report);
}

显示地面站信息：

通过这样的组合，我们就在地面站上看到了 熟悉的 PreArm: Barometer not healthy