RCInput

Class that takes care of RC (Radio Control) input signals. This signals are usually either PPM (PPM-SUM), PWM, D-BUS or other sort of RC starndart. This class implements a layer to abstract linux-based systems.

This class is still a work in progress.

This class is divided into two files, header (RCInput.h) and source code (RCInput.cpp).

RCInput.h

Link to the code:RCInput.h

Linux::LinuxRCInputdefines the methods inherited from the AP_HAL::RCInput abstract class, for handling Radio Control (RC) input signals processing like telemetry.

#ifndef __AP_HAL_LINUX_RCINPUT_H__
#define __AP_HAL_LINUX_RCINPUT_H__

#include <AP_HAL_Linux.h>

class Linux::LinuxRCInput : public AP_HAL::RCInput {
public:
    LinuxRCInput();
    void init(void* machtnichts);
    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:
    bool new_rc_input;

    /* override state */
    uint16_t _override[8];
};

#endif // __AP_HAL_LINUX_RCINPUT_H__

• Defines the LinuxRCInputclass that inherits from AP_HAL::RCInput.

• The init method is defined. Call init from the platform hal instance init, so that both the type of the RCInput implementation and init argument are known to the programmer.

• There are some method defined for later implementation in RCInput.cpp.

RCInput.cpp

RCInput.cpp implements the methods defined in RCInput.h header file for read and override the RC input channels.

...
#include <AP_HAL.h>

#if CONFIG_HAL_BOARD == HAL_BOARD_LINUX

#include "RCInput.h"

using namespace Linux;
LinuxRCInput::LinuxRCInput() :
new_rc_input(false)
{}

void LinuxRCInput::init(void* machtnichts)
{}


...

• AP_HAL.hand RCInput.h are imported and the board is defined.

• Note that new_rc_input is initialized to False.

...
bool LinuxRCInput::new_input()
{
    return new_rc_input;
}
...

• This method returns true if there has been new input since the last read() call.

...

uint8_t LinuxRCInput::num_channels()
{
    return 8;
}
...

• This slice of code returns the number of valid channels in the last read.

...
uint16_t LinuxRCInput::read(uint8_t ch)
{
    new_rc_input = false;
    if (_override[ch]) {
        return _override[ch];
    }
    if (ch == 2) {
        // force low throttle for now
        return 900;
    }
    return 1500;
}
...

• read() reads a single channel at a time.

...
uint8_t LinuxRCInput::read(uint16_t* periods, uint8_t len)
{
    for (uint8_t i=0; i<len; i++) {
    periods[i] = read(i);
    }
    return 8;
}
...

• This method reads an array of channels, return the valid count. Note that the name is th e same as the previous one, that means that the one we select depend on the arguments.

...
bool LinuxRCInput::set_overrides(int16_t *overrides, uint8_t len)
{
    bool res = false;
    for (uint8_t i = 0; i < len; i++) {
        res |= set_override(i, overrides[i]);
    }
    return res;
}

bool LinuxRCInput::set_override(uint8_t channel, int16_t override)
{
    if (override < 0) return false; /* -1: no change. */
    if (channel < 8) {
        _override[channel] = override;
        if (override != 0) {
            new_rc_input = true;
            return true;
        }
    }
    return false;
}

void LinuxRCInput::clear_overrides()
{
    for (uint8_t i = 0; i < 8; i++) {
    _override[i] = 0;
    }
}

• This method do the following:
  • The first set_overrides: array starts at ch 0, for len channels.
  • The second set_override: set just a specific channel .
  • The last set_override: equivelant to setting all overrides to 0 .