ardupilot/libraries/AP_HAL/examples/RCInputToRCOutput/RCInputToRCOutput.cpp

/*
    RC input pass trough to RC output
    Max RC channels 14
    Max update rate 10 Hz
*/

#include <AP_HAL/AP_HAL.h>

const AP_HAL::HAL& hal = AP_HAL::get_HAL();

#define MAX_CHANNELS 14

static uint8_t max_channels = 0;
static uint16_t last_value[MAX_CHANNELS];

void setup(void) 
{
    hal.console->printf("Starting RCInputToRCOutput test\n");

    for(uint8_t i = 0; i < MAX_CHANNELS; i++) {
        hal.rcout->enable_ch(i);
    }
}

void loop(void) 
{
    bool changed = false;
    uint8_t nchannels = hal.rcin->num_channels();

    if(nchannels > MAX_CHANNELS) {
       nchannels = MAX_CHANNELS;
    }

    for(uint8_t i = 0; i < nchannels; i++) {
        uint16_t v = hal.rcin->read(i);
        if(last_value[i] != v) {
            hal.rcout->write(i, v);
            changed = true;
            last_value[i] = v;
        }
        if(i > max_channels) {
            max_channels = i;
        }
    }
    if(changed) {
        for(uint8_t i = 0; i < max_channels; i++) {
            hal.console->printf("%2u:%04u ", (unsigned)i + 1, (unsigned)last_value[i]);
        }
        hal.console->printf("\n");
    }
    hal.scheduler->delay(100);
}

AP_HAL_MAIN();