可以看到飞控具有16个ic输出通道，理论上每一个通道都可以单独输出pwm，那么怎样才能在固件中让每个通道都单独输出pwm呢？
1、
手动模式下油门控制可以直观的控制pwm输出，
在void ModeManual::update()中可以看到g2.motors.set_throttle(desired_throttle); 就是油门处理函数。可以根据这个函数寻址找到void AP_MotorsUGV::set_throttle(float throttle)函数
//libraries/AR_Motors/AP_MotorsUGV.cpp
void AP_MotorsUGV::set_throttle(float throttle)
{// only allow setting throttle if armedif (!hal.util->get_soft_armed()) {return;}// check throttle is between -_throttle_max and +_throttle_max_throttle = constrain_float(throttle, -_throttle_max, _throttle_max);
}在这个函数中可以看到形参desired_throttle最终是递给了_throttle这个参数。接下来就是在该文件下找哪里使用了_throttle这个参数。
void AP_MotorsUGV::output(bool armed, float ground_speed, float dt)
{// soft-armed overrides passed in armed status 以武装状态通过软武装覆盖if (!hal.util->get_soft_armed()) {armed = false;_throttle = 0.0f;}// clear limit flags// output_ methods are responsible for setting them to true if required on each iteration//清除限制标志//output_方法负责在每次迭代中根据需要将其设置为truelimit.steer_left = limit.steer_right = limit.throttle_lower = limit.throttle_upper = false;// sanity check parameters 健全性检查参数sanity_check_parameters();// slew limit throttle 回转限制节流阀slew_limit_throttle(dt);// output for regular steering/throttle style frames 常规转向/油门式车架的输出output_regular(armed, ground_speed, _steering, _throttle);// output for skid steering style frames 滑移转向式车架的输出output_skid_steering(armed, _steering, _throttle, dt);// output for omni frames 全帧输出output_omni(armed, _steering, _throttle, _lateral);// output to sails 输出到帆output_sail();// send values to the PWM timers for output 将值发送到PWM定时器进行输出SRV_Channels::calc_pwm(); //计算所有通道的PWMSRV_Channels::cork();SRV_Channels::output_ch_all(); //控制pwm输出SRV_Channels::push();
}搜索查找后可以找到void AP_MotorsUGV::output(bool armed, float ground_speed, float dt)这个函数，看名称可以判断为输出函数。_throttle在这个函数中使用了，但是最终都汇聚在SRV_Channels::output_ch_all();函数中，这个就是控制pwm输出函数。
继续寻址。找到SRV_Channels::output_ch_all()的定义。
//libraries/SRV Channel/SRV Channel_aux.cpp
void SRV_Channels::output_ch_all(void)
{uint8_t max_chan = NUM_SERVO_CHANNELS;
#if NUM_SERVO_CHANNELS >= 17if (_singleton != nullptr && _singleton->enable_32_channels.get() <= 0) {max_chan = 16;}
#endiffor (uint8_t i = 0; i < max_chan; i++) {channels[i].output_ch();}
}在函数的末尾可以看到channels[i].output_ch();这个函数，这个函数还不能直接输出定值的pwm，继续寻址。
//libraries/SRV Channel/SRV Channel_aux.cpp
void SRV_Channel::output_ch(void)
{
#ifndef HAL_BUILD_AP_PERIPHint8_t passthrough_from = -1;bool passthrough_mapped = false;// take care of special function cases 照顾特殊功能例switch(function.get()){case k_manual: // manualpassthrough_from = ch_num;break;case k_rcin1 ... k_rcin16: // rc pass-thrupassthrough_from = int8_t((int16_t)function - k_rcin1);break;case k_rcin1_mapped ... k_rcin16_mapped:passthrough_from = int8_t((int16_t)function - k_rcin1_mapped);passthrough_mapped = true;break;}if (passthrough_from != -1) {// we are doing passthrough from input to output for this channel 我们正在为这个通道进行从输入到输出的直通RC_Channel *c = rc().channel(passthrough_from);if (c) {if (SRV_Channels::passthrough_disabled()) {output_pwm = c->get_radio_trim();} else {// non-mapped rc passthrough 非映射rc透传int16_t radio_in = c->get_radio_in();if (passthrough_mapped) {if (rc().has_valid_input()) {switch (c->get_type()) {case RC_Channel::ControlType::ANGLE:radio_in = pwm_from_angle(c->norm_input_dz() * 4500);break;case RC_Channel::ControlType::RANGE:// convert RC normalised input from -1 to +1 range to 0 to +1 and output as rangeradio_in = pwm_from_range((c->norm_input_ignore_trim() + 1.0) * 0.5 * 4500);break;}} else {// no valid input. If we are in radio// failsafe then go to trim values (if// configured for this channel). Otherwise// use the last-good valueif ( ((1U<<passthrough_from) & SRV_Channels::get_rc_fs_mask()) && rc().in_rc_failsafe()) {radio_in = pwm_from_angle(0);} else {radio_in = previous_radio_in;}}}if (!ign_small_rcin_changes) {output_pwm = radio_in;previous_radio_in = radio_in;} else {// check if rc input value has changed by more than the deadzoneif (abs(radio_in - previous_radio_in) > c->get_dead_zone()) {output_pwm = radio_in;ign_small_rcin_changes = false;}}}}}
#endif // HAL_BUILD_AP_PERIPHif (!(SRV_Channels::disabled_mask & (1U<<ch_num))) {// hal.rcout->write(ch_num, output_pwm);//原版hal.rcout->write(ch_num, 900+ch_num*70);//实验测试}
}该函数下，前面的都是验证每个通道分别需要多少的pwm输出，函数的最后才是控制单独通道的单独输出。
hal.rcout->write(ch_num, output_pwm);其中ch_num即对应通道，output_pwm即需要输出的pwm，在这里修改代码测试一下：
hal.rcout->write(ch_num, 900+ch_num*70);修改后，理论上第一个通道输出900，然后后面的通道逐个递增70。
编译完成后下载到飞控中查看ic通道输出。
可以看到ic通道确实是根据设定输出，但是只有前8个通道输出，后面8个却没有输出，这是为啥？
