EasyARM i.mx28学习笔记——文件IO方式操作GPIO

static int gpio_export(int pin)
{
    char buffer[BUFFER_MAX];
    int len;
    int fd;

    fd = open("/sys/class/gpio/export", O_WRONLY);
    if (fd < 0) {
        fprintf(stderr, "Failed to open export for writing!\n");
        return(-1);
    }

    len = snprintf(buffer, BUFFER_MAX, "%d", pin);
    if (write(fd, buffer, len) < 0) {
        fprintf(stderr, "Fail to export gpio!");
        return -1;
    }
   
    close(fd);
    return 0;
}

static int gpio_unexport(int pin)
{
    char buffer[BUFFER_MAX];
    int len;
    int fd;

    fd = open("/sys/class/gpio/unexport", O_WRONLY);
    if (fd < 0) {
        fprintf(stderr, "Failed to open unexport for writing!\n");
        return -1;
    }

    len = snprintf(buffer, BUFFER_MAX, "%d", pin);
    if (write(fd, buffer, len) < 0) {
        fprintf(stderr, "Fail to unexport gpio!");
        return -1;
    }
   
    close(fd);
    return 0;
}

static int gpio_direction(int pin, int dir)
{
    static const char dir_str[] = "in\0out";
    char path[DIRECTION_MAX];
    int fd;

    snprintf(path, DIRECTION_MAX, "/sys/class/gpio/gpio%d/direction", pin);
    fd = open(path, O_WRONLY);
    if (fd < 0) {
        fprintf(stderr, "failed to open gpio direction for writing!\n");
        return -1;
    }

    if (write(fd, &dir_str[dir == IN ? 0 : 3], dir == IN ? 2 : 3) < 0) {
        fprintf(stderr, "failed to set direction!\n");
        return -1;
    }

    close(fd);
    return 0;
}

static int gpio_write(int pin, int value)
{
    static const char values_str[] = "01";
    char path[DIRECTION_MAX];
    int fd;

    snprintf(path, DIRECTION_MAX, "/sys/class/gpio/gpio%d/value", pin);
    fd = open(path, O_WRONLY);
    if (fd < 0) {
        fprintf(stderr, "failed to open gpio value for writing!\n");
        return -1;
    }

    if (write(fd, &values_str[value == LOW ? 0 : 1], 1) < 0) {
        fprintf(stderr, "failed to write value!\n");
        return -1;
    }

    close(fd);
    return 0;
}

static int gpio_read(int pin)
{
    char path[DIRECTION_MAX];
    char value_str[3];
    int fd;

    snprintf(path, DIRECTION_MAX, "/sys/class/gpio/gpio%d/value", pin);
    fd = open(path, O_RDONLY);
    if (fd < 0) {
        fprintf(stderr, "failed to open gpio value for reading!\n");
        return -1;
    }

    if (read(fd, value_str, 3) < 0) {
        fprintf(stderr, "failed to read value!\n");
        return -1;
    }

    close(fd);
    return (atoi(value_str));
}

int main(int argc, char *argv[])
{
    int i = 0;
    gpio_export(P24);

    gpio_direction(P24, OUT); // GPIO为输出状态
    for (i = 0; i < 10; i++) {
        printf("LED Blink\n");
        gpio_write(P24, i % 2);
        usleep(500 * 1000);
    }
    gpio_write(P24, 0); // 恢复输出低电平

    gpio_unexport(P24);
    return 0;
}

# 可执行文件
TARGET=test
# 源文件
SRCS=gpio-sysfs.c

# 目标文件
OBJS=$(SRCS:.c=.o)

# 指令编译器和选项
CROSS=arm-fsl-linux-gnueabi-
CC=$(CROSS)gcc
STRIP=$(CROSS)strip
CFLAGS=-Wall -std=gnu99 -O2

$(TARGET):$(OBJS)
 $(CC) -o $@ $^
 $(STRIP) $@

clean:
 rm -rf $(TARGET) $(OBJS)

# 连续动作，先清除再编译链接，复制到tftpboot中
install:clean $(TARGET)
 @echo 复制到tftpboot目录
 cp $(TARGET) ~/tftpboot
 @echo 复制结束

# 编译规则 $@代表目标文件 $< 代表第一个依赖文件
%.o:%.c
 $(CC) $(CFLAGS) -o $@ -c $<

#!/bin/sh                                                                       
tftp -g -r test 192.168.1.106                                                   
chmod a+x test                                                                  
echo "start to run test."                                                       
./test