ardupilot/libraries/AP_HAL_AVR/RCInput.h

#ifndef __AP_HAL_AVR_RC_INPUT_H__
#define __AP_HAL_AVR_RC_INPUT_H__

#include <AP_HAL.h>
#include "AP_HAL_AVR_Namespace.h"

#define AVR_RC_INPUT_NUM_CHANNELS 11
#define AVR_RC_INPUT_MIN_CHANNELS 5     // for ppm sum we allow less than 8 channels to make up a valid packet

/*
  mininum pulse width in microseconds to signal end of a PPM-SUM
  frame. This value is chosen to be smaller than the default 3000 sync
  pulse width for OpenLRSng. Note that this is the total pulse with
  (typically 300us low followed by a long high pulse)
 */
#define AVR_RC_INPUT_MIN_SYNC_PULSE_WIDTH 2700

class AP_HAL_AVR::APM1RCInput : public AP_HAL::RCInput {
public:
    /**
     * init:
     * HAL_AVR::init should pass in a AP_HAL_AVR::ISRRegistry* as a void*
     */
    void     init(void* isrregistry);

    /**
     * Return true if there has been new input since the last read()
     * call. This call also clears the new_input flag, so once it
     * returns true it won't return true again until another frame is
     * received.
     */
    bool  new_input();

    /**
     * Return the number of input channels in last read()
     */
    uint8_t num_channels();

    /**
     * read(uint8_t):
     * Read a single channel at a time
     */
    uint16_t read(uint8_t ch);

    /**
     * read(uint16_t*,uint8_t):
     * Read an array of channels, return the valid count
     */
    uint8_t  read(uint16_t* periods, uint8_t len);

    /**
     * Overrides: these are really grody and don't belong here but we need
     * them at the moment to make the port work.
     * case v of:
     *  v == -1 -> no change to this channel
     *  v == 0  -> do not override this channel
     *  v > 0   -> set v as override.
     */

    /* set_overrides: array starts at ch 0, for len channels */
    bool set_overrides(int16_t *overrides, uint8_t len);
    /* set_override: set just a specific channel */
    bool set_override(uint8_t channel, int16_t override);
    /* clear_overrides: equivelant to setting all overrides to 0 */
    void clear_overrides();

private:
    /* private callback for input capture ISR */
    static void _timer4_capt_cb(void);
    /* private variables to communicate with input capture isr */
    static volatile uint16_t _pulse_capt[AVR_RC_INPUT_NUM_CHANNELS];
    static volatile uint8_t  _num_channels;
    static volatile bool     _new_input;

    /* override state */
    uint16_t _override[AVR_RC_INPUT_NUM_CHANNELS]; 
};

class AP_HAL_AVR::APM2RCInput : public AP_HAL::RCInput {
    /* Pass in a AP_HAL_AVR::ISRRegistry* as void*. */
    void     init(void* isrregistry);
    bool  new_input();
    uint8_t num_channels();
    uint16_t read(uint8_t ch);
    uint8_t  read(uint16_t* periods, uint8_t len);
    bool set_overrides(int16_t *overrides, uint8_t len);
    bool set_override(uint8_t channel, int16_t override);
    void clear_overrides();
private:
    /* private callback for input capture ISR */
    static void _timer5_capt_cb(void);
    /* private variables to communicate with input capture isr */
    static volatile uint16_t _pulse_capt[AVR_RC_INPUT_NUM_CHANNELS];
    static volatile uint8_t  _num_channels;
    static volatile bool  _new_input;

    /* override state */
    uint16_t _override[AVR_RC_INPUT_NUM_CHANNELS]; 
};

#endif // __AP_HAL_AVR_RC_INPUT_H__