ardupilot/libraries/AP_HAL_AVR/GPIO.cpp

#include <avr/interrupt.h>
#include <avr/io.h>

#include "pins_arduino_mega.h"

#include "GPIO.h"
using namespace AP_HAL_AVR;


AP_HAL::Proc AVRGPIO::_interrupt_6 = NULL;

SIGNAL(INT6_vect) {
    if (AVRGPIO::_interrupt_6) {
        AVRGPIO::_interrupt_6();
    }
}   

// Get the bit location within the hardware port of the given virtual pin.
// This comes from the pins_*.c file for the active board configuration.

#define analogInPinToBit(P) (P)


// Get the bit location within the hardware port of the given virtual pin.
// This comes from the pins_*.c file for the active board configuration.
// 
// These perform slightly better as macros compared to inline functions
//
#define digitalPinToPort(P) ( pgm_read_byte( digital_pin_to_port_PGM + (P) ) )
#define digitalPinToBitMask(P) ( pgm_read_byte( digital_pin_to_bit_mask_PGM + (P) ) )
#define digitalPinToTimer(P) ( pgm_read_byte( digital_pin_to_timer_PGM + (P) ) )
#define analogInPinToBit(P) (P)
#define portOutputRegister(P) ( (volatile uint8_t *)( pgm_read_word( port_to_output_PGM + (P))) )
#define portInputRegister(P) ( (volatile uint8_t *)( pgm_read_word( port_to_input_PGM + (P))) )
#define portModeRegister(P) ( (volatile uint8_t *)( pgm_read_word( port_to_mode_PGM + (P))) )


void AVRGPIO::pinMode(uint8_t pin, uint8_t mode) {
    uint8_t bit = digitalPinToBitMask(pin);
    uint8_t port = digitalPinToPort(pin);
    volatile uint8_t *reg;

    if (port == NOT_A_PIN) return;

    // JWS: can I let the optimizer do this?
    reg = portModeRegister(port);

    if (mode == GPIO_INPUT) {
        uint8_t oldSREG = SREG;
                cli();
        *reg &= ~bit;
        SREG = oldSREG;
    } else {
        uint8_t oldSREG = SREG;
                cli();
        *reg |= bit;
        SREG = oldSREG;
    }
}

uint8_t AVRGPIO::read(uint8_t pin) {
    uint8_t bit = digitalPinToBitMask(pin);
    uint8_t port = digitalPinToPort(pin);

    if (port == NOT_A_PIN) return 0;

    if (*portInputRegister(port) & bit) return 1;
    return 0;
}

void AVRGPIO::write(uint8_t pin, uint8_t value) {
    uint8_t bit = digitalPinToBitMask(pin);
    uint8_t port = digitalPinToPort(pin);
    volatile uint8_t *out;

    if (port == NOT_A_PIN) return;

    out = portOutputRegister(port);

    uint8_t oldSREG = SREG;
    cli();

    if (value == 0) {
        *out &= ~bit;
    } else {
        *out |= bit;
    }

    SREG = oldSREG;
}

/* Implement GPIO Interrupt 6, used for MPU6000 data ready on APM2. */
bool AVRGPIO::attach_interrupt(
        uint8_t interrupt_num, AP_HAL::Proc proc, uint8_t mode) {
    if (!((mode == 0)||(mode == 1))) return false;
    if (interrupt_num == 6) {
        _interrupt_6 = proc;
        EICRB = (EICRB & ~((1 << ISC60) | (1 << ISC61))) | (mode << ISC60);
        EIMSK |= (1 << INT6);
        return true;
    } else {
        return false;
    }
}


AP_HAL::DigitalSource* AVRGPIO::channel(uint16_t pin) {
    uint8_t bit = digitalPinToBitMask(pin);
    uint8_t port = digitalPinToPort(pin);
    if (port == NOT_A_PIN) return NULL;
    return new AVRDigitalSource(bit, port);
}

void AVRDigitalSource::mode(uint8_t output) {
    const uint8_t bit = _bit;
    const uint8_t port = _port;

    volatile uint8_t* reg;
    reg = portModeRegister(port);

    if (output == GPIO_INPUT) {
        uint8_t oldSREG = SREG;
                cli();
        *reg &= ~bit;
        SREG = oldSREG;
    } else {
        uint8_t oldSREG = SREG;
                cli();
        *reg |= bit;
        SREG = oldSREG;
    }
}

uint8_t AVRDigitalSource::read() {
    const uint8_t bit = _bit;
    const uint8_t port = _port;
    if (*portInputRegister(port) & bit) return 1;
    return 0;
}

void AVRDigitalSource::write(uint8_t value) {
    const uint8_t bit = _bit;
    const uint8_t port = _port;
    volatile uint8_t* out;
    out = portOutputRegister(port);

    uint8_t oldSREG = SREG;
    cli();

    if (value == 0) {
        *out &= ~bit;
    } else {
        *out |= bit;
    }

    SREG = oldSREG;
}