162 lines
3.0 KiB
C
162 lines
3.0 KiB
C
/*
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* C Implementation: gpio
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*
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* Description:
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*
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*
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* Author: Paolo Zebelloni <p.zebelloni@c-labs-wt.com>, (C) 2014
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*
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* Copyright: See COPYING file that comes with this distribution
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*
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <errno.h>
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#include <unistd.h>
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#include <sys/signal.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include "gpio.h"
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#define SYSFS_GPIO_DIR "/sys/class/gpio"
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#define MAX_BUF 64
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/**
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* Before a Linux application can configure and use a GPIO, the GPIO first has to be exported to user.
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* Each GPIO is not accessible from user space until the GPIO has been exported.
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* You can only export a GPIO that isn't owned by a Linux kernel driver
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* @param gpio GPIO number
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* @return 0 if OK, -1 if fails
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*/
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int gpio_export ( unsigned int gpio )
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{
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int fd, len;
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char buf[MAX_BUF];
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fd = open ( SYSFS_GPIO_DIR "/export", O_WRONLY );
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if ( fd < 0 )
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{
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perror ( "gpio/export" );
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return -1;
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}
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len = snprintf ( buf, sizeof ( buf ), "%d", gpio );
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write ( fd, buf, len );
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close ( fd );
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return 0;
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}
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/**
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* Complement of gpio_export().
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* @param gpio GPIO number
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* @return 0 if OK, -1 if fails
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*/
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int gpio_unexport ( unsigned int gpio )
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{
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int fd, len;
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char buf[MAX_BUF];
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fd = open ( SYSFS_GPIO_DIR "/unexport", O_WRONLY );
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if ( fd < 0 )
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{
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perror ( "gpio/unexport" );
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return -1;
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}
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len = snprintf ( buf, sizeof ( buf ), "%d", gpio );
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write ( fd, buf, len );
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close ( fd );
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return 0;
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}
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/**
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* To avoid hardware issues where two devices are driving the same signal, GPIOs default to be configured as an input.
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* If you want to use the GPIO as an output, you need to change the configuration
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* @param gpio GPIO number
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* @param out_flag TRUE means OUT, FALSE means IN
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* @return 0 if OK, -1 if fails
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*/
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int gpio_set_dir ( unsigned int gpio, unsigned int out_flag )
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{
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int fd;
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char buf[MAX_BUF];
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snprintf ( buf, MAX_BUF, SYSFS_GPIO_DIR "/gpio%d/direction", gpio );
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fd = open ( buf, O_WRONLY );
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if ( fd < 0 )
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{
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perror ( "gpio/direction" );
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return -1;
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}
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if ( out_flag )
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write ( fd, "out", 4 );
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else
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write ( fd, "in", 3 );
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close ( fd );
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return 0;
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}
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/**
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* Set HI or LO state to GPIO (output) pin.
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* @param gpio GPIO number
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* @param value TRUE means HI, FALSE means LO
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* @return 0 if OK, -1 if fails
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*/
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int gpio_set_value ( unsigned int gpio, unsigned int value )
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{
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int fd;
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char buf[MAX_BUF];
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snprintf ( buf, MAX_BUF, SYSFS_GPIO_DIR "/gpio%d/value", gpio );
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fd = open ( buf, O_WRONLY );
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if ( fd < 0 )
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{
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perror ( "gpio/set-value" );
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return -1;
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}
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write ( fd, value ? "1" : "0", 2 );
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close ( fd );
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return 0;
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}
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/**
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* Read state of GPIO (input) pin.
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* @param gpio GPIO number
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* @return 0 if LO, 1 if HI, -1 if fails
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*/
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int gpio_get_value ( unsigned int gpio )
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{
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int fd;
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char buf[MAX_BUF];
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char ch;
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snprintf ( buf, MAX_BUF, SYSFS_GPIO_DIR "/gpio%d/value", gpio );
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fd = open ( buf, O_RDONLY );
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if ( fd < 0 )
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{
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perror ( "gpio/get-value" );
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return -1;
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}
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read ( fd, &ch, 1 );
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close ( fd );
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return ( ch != '0' );
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}
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