linux_gpio.cpp

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 *   Copyright (c) 2016 - 2017 PX4 Development Team. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 *    notice, this list of conditions and the following disclaimer.
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 *    used to endorse or promote products derived from this software
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#include "linux_gpio.h"

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>

#include <px4_platform_common/posix.h>

#define PIN_INDEX_BUFFER_MAX (16)
#define PIN_DIRECTION_BUFFER_MAX (30 + PIN_INDEX_BUFFER_MAX)
#define PIN_VALUE_BUFFER_MAX (26 + PIN_INDEX_BUFFER_MAX)

LinuxGPIO::LinuxGPIO(unsigned int pin)
    : _pin(pin)
    , _fd(-1)
{
}

LinuxGPIO::~LinuxGPIO()
{
    if (_fd != -1) {
        close(_fd);
    }
}

int LinuxGPIO::exportPin()
{
    int ret;
    char pinIndex[PIN_INDEX_BUFFER_MAX];
    char valuePath[PIN_VALUE_BUFFER_MAX];
    int fd = -1;
    int bytes_to_write;

    struct stat statbuf;

    /* If GPIO was already opened, close it */
    if (_fd != -1) {
        close(_fd);
        _fd = -1;
    }

    /* Check if GPIO is already exported */
    snprintf(valuePath, PIN_VALUE_BUFFER_MAX, "/sys/class/gpio/gpio%d/value", _pin);
    ret = stat(valuePath, &statbuf);

    if (ret == -1) {
        /* GPIO is not exported */
        fd = open("/sys/class/gpio/export", O_WRONLY);

        if (fd == -1) {
            int err = errno;
            PX4_ERR("export %u: open: %s (%d)", _pin, strerror(err), err);
            return -1;
        }

        bytes_to_write = snprintf(pinIndex, PIN_INDEX_BUFFER_MAX, "%u", _pin);
        ret = write(fd, pinIndex, bytes_to_write);

        if (ret == -1) {
            int err = errno;
            PX4_ERR("export %u: write: %s (%d)", _pin, strerror(err), err);
            goto cleanup;

        } else if (ret != bytes_to_write) {
            PX4_ERR("export %u: write incomplete %d != %d", _pin, ret, bytes_to_write);
            goto cleanup;
        }
    }

    _fd = open(valuePath, O_RDWR);

    if (_fd == -1) {
        int err = errno;
        ret = -1;
        PX4_ERR("export %u: open: %s (%d)", _pin, strerror(err), err);
        goto cleanup;
    }

    ret = 0;

cleanup:

    if (fd != -1) {
        close(fd);
    }

    return ret;
}

int LinuxGPIO::unexportPin()
{
    char pinIndex[PIN_INDEX_BUFFER_MAX];
    int fd;
    int ret;
    int bytes_to_write;

    if (_fd != -1) {
        close(_fd);
        _fd = -1;
    }

    fd = open("/sys/class/gpio/unexport", O_WRONLY);

    if (fd == -1) {
        int err = errno;
        PX4_ERR("unexport %u: open: %s (%d)", _pin, strerror(err), err);
        return -1;
    }

    bytes_to_write = snprintf(pinIndex, PIN_INDEX_BUFFER_MAX, "%u", _pin);
    ret = write(fd, pinIndex, bytes_to_write);

    if (ret == -1) {
        int err = errno;
        PX4_ERR("unexport %u: write: %s (%d)", _pin, strerror(err), err);
        goto cleanup;

    } else if (ret != bytes_to_write) {
        PX4_ERR("unexport %u: write incomplete %d != %d", _pin, ret, bytes_to_write);
        goto cleanup;
    }

    ret = 0;

cleanup:
    close(fd);

    return ret;
}

int LinuxGPIO::setDirection(LinuxGPIO::Direction dir)
{
    char path[PIN_DIRECTION_BUFFER_MAX];
    int fd;
    int ret;

    snprintf(path, PIN_DIRECTION_BUFFER_MAX, "/sys/class/gpio/gpio%d/direction", _pin);
    fd = open(path, O_WRONLY);

    if (fd == -1) {
        int err = errno;
        PX4_ERR("dir %u: open: %s (%d)", _pin, strerror(err), err);
        return -1;
    }

    if (dir == Direction::IN) {
        ret = write(fd, "in", 2);

    } else {
        ret = write(fd, "out", 3);
    }

    if (ret == -1) {
        int err = errno;
        PX4_ERR("dir %u: write: %s (%d)", _pin, strerror(err), err);
        goto cleanup;
    }

    ret = 0;

cleanup:
    close(fd);

    return ret;
}

int LinuxGPIO::readValue()
{
    char buf[2];
    int ret;

    ret = ::read(_fd, buf, sizeof(buf));

    if (ret == -1) {
        int err = errno;
        PX4_ERR("readValue %u: read: %s (%d)", _pin, strerror(err), err);
        return ret;
    }

    ret = strtol(buf, nullptr, 10);

    return ret;
}

int LinuxGPIO::writeValue(LinuxGPIO::Value value)
{
    char buf[2];
    int ret;

    if (value != Value::LOW && value != Value::HIGH) {
        return -EINVAL;
    }

    int buflen = snprintf(buf, sizeof(buf), "%u", (unsigned int)value);

    ret = ::write(_fd, buf, buflen);

    if (ret == -1) {
        int err = errno;
        PX4_ERR("writeValue %u: write: %s (%d)", _pin, strerror(err), err);
        return ret;
    }

    return 0;
}