Linux下用文件IO的方式操作GPIO

Linux下用文件IO的方式操作GPIO（/sys/class/gpio）  通过sysfs方式控制GPIO，先访问/sys/class/gpio目录，向export文件写入GPIO编号，使得该GPIO的操作接口从内核空间暴露到用户空间，GPIO的操作接口包括direction和value等，direction控制GPIO方向，而value可控制GPIO输出或获得GPIO输入。文件IO方式操作GPIO，使用到了4个函数open、close、read、write。首先，看看系统中有没有“/sys/class/gpio”这个文件夹。如果没有请在编译内核的时候加入 Device Drivers-> GPIO Support ->/sys/class/gpio/… (sysfs interface)。/sys/class/gpio 的使用说明：gpio_operation 通过/sys/文件接口操作IO端口 GPIO到文件系统的映射◇ 控制GPIO的目录位于/sys/class/gpio◇ /sys/class/gpio/export文件用于通知系统需要导出控制的GPIO引脚编号◇ /sys/class/gpio/unexport 用于通知系统取消导出◇ /sys/class/gpio/gpiochipX目录保存系统中GPIO寄存器的信息，包括每个寄存器控制引脚的起始编号base，寄存器名称，引脚总数 导出一个引脚的操作步骤◇ 首先计算此引脚编号，引脚编号 = 控制引脚的寄存器基数 + 控制引脚寄存器位数◇ 向/sys/class/gpio/export写入此编号，比如12号引脚，在shell中可以通过以下命令实现，命令成功后生成/sys/class/gpio/gpio12目录，如果没有出现相应的目录，说明此引脚不可导出◇ direction文件，定义输入输入方向，可以通过下面命令定义为输出。direction接受的参数：in, out, high, low。high/low同时设置方向为输出，并将value设置为相应的1/0◇ value文件是端口的数值，为1或0几个例子：1. 导出/sys/class/gpio# echo 44 > export2. 设置方向/sys/class/gpio/gpio44# echo out > direction3. 查看方向/sys/class/gpio/gpio44# cat direction4. 设置输出/sys/class/gpio/gpio44# echo 1 > value5. 查看输出值/sys/class/gpio/gpio44# cat value6. 取消导出/sys/class/gpio# echo 44 > unexport文件读写例程：#include stdlib.h #include stdio.h #include string.h#include unistd.h#include fcntl.h //define O_WRONLY and O_RDONLY //芯片复位引脚: P1_16#define SYSFS_GPIO_EXPORT "/sys/class/gpio/export" #define SYSFS_GPIO_RST_PIN_VAL "48" #define SYSFS_GPIO_RST_DIR "/sys/class/gpio/gpio48/direction"#define SYSFS_GPIO_RST_DIR_VAL "OUT" #define SYSFS_GPIO_RST_VAL "/sys/class/gpio/gpio48/value"#define SYSFS_GPIO_RST_VAL_H "1"#define SYSFS_GPIO_RST_VAL_L "0"int main() { int fd; //打开端口/sys/class/gpio# echo 48 > exportfd = open(SYSFS_GPIO_EXPORT, O_WRONLY);if(fd == -1){printf("ERR: Radio hard reset pin open error.\n");return EXIT_FAILURE;}write(fd, SYSFS_GPIO_RST_PIN_VAL ,sizeof(SYSFS_GPIO_RST_PIN_VAL)); close(fd); //设置端口方向/sys/class/gpio/gpio48# echo out > directionfd = open(SYSFS_GPIO_RST_DIR, O_WRONLY);if(fd == -1){printf("ERR: Radio hard reset pin direction open error.\n");return EXIT_FAILURE;}write(fd, SYSFS_GPIO_RST_DIR_VAL, sizeof(SYSFS_GPIO_RST_DIR_VAL)); close(fd); //输出复位信号: 拉高>100nsfd = open(SYSFS_GPIO_RST_VAL, O_RDWR);if(fd == -1){printf("ERR: Radio hard reset pin value open error.\n");return EXIT_FAILURE;} while(1){write(fd, SYSFS_GPIO_RST_VAL_H, sizeof(SYSFS_GPIO_RST_VAL_H));usleep(1000000);write(fd, SYSFS_GPIO_RST_VAL_L, sizeof(SYSFS_GPIO_RST_VAL_L));usleep(1000000);}close(fd);printf("INFO: Radio hard reset pin value open error.\n");return 0;} 另外参考网上一个网友的程序，这里做了验证，并实现中断检测函数。如下：#include stdlib.h #include stdio.h #include string.h#include unistd.h#include fcntl.h #include poll.h#define MSG(args...) printf(args)//函数声明static int gpio_export(int pin);static int gpio_unexport(int pin);static int gpio_direction(int pin, int dir);static int gpio_write(int pin, int value);static int gpio_read(int pin);static int gpio_export(int pin) { char buffer[64]; int len; int fd; fd = open("/sys/class/gpio/export", O_WRONLY); if (fdMSG("Failed to open export for writing!\n"); return(-1); } len = snprintf(buffer, sizeof(buffer), "%d", pin); if (write(fd, buffer, len)MSG("Failed to export gpio!"); return -1; } close(fd); return 0; }static int gpio_unexport(int pin) { char buffer[64]; int len; int fd; fd = open("/sys/class/gpio/unexport", O_WRONLY); if (fdMSG("Failed to open unexport for writing!\n"); return -1; } len = snprintf(buffer, sizeof(buffer), "%d", pin); if (write(fd, buffer, len)MSG("Failed to unexport gpio!"); return -1; } close(fd); return 0; }//dir: 0-->IN, 1-->OUTstatic int gpio_direction(int pin, int dir) { static const char dir_str[] = "in\0out"; char path[64]; int fd; snprintf(path, sizeof(path), "/sys/class/gpio/gpio%d/direction", pin); fd = open(path, O_WRONLY); if (fdMSG("Failed to open gpio direction for writing!\n"); return -1; } if (write(fd, &dir_str[dir == 0 ? 0 : 3], dir == 0 ? 2 : 3)MSG("Failed to set direction!\n"); return -1; } close(fd); return 0; }//value: 0-->LOW, 1-->HIGHstatic int gpio_write(int pin, int value) { static const char values_str[] = "01"; char path[64]; int fd; snprintf(path, sizeof(path), "/sys/class/gpio/gpio%d/value", pin); fd = open(path, O_WRONLY); if (fdMSG("Failed to open gpio value for writing!\n"); return -1; } if (write(fd, &values_str[value == 0 ? 0 : 1], 1)MSG("Failed to write value!\n"); return -1; } close(fd); return 0; }static int gpio_read(int pin) { char path[64]; char value_str[3]; int fd; snprintf(path, sizeof(path), "/sys/class/gpio/gpio%d/value", pin); fd = open(path, O_RDONLY); if (fdMSG("Failed to open gpio value for reading!\n"); return -1; } if (read(fd, value_str, 3)MSG("Failed to read value!\n"); return -1; } close(fd); return (atoi(value_str));}// none表示引脚为输入，不是中断引脚// rising表示引脚为中断输入，上升沿触发// falling表示引脚为中断输入，下降沿触发// both表示引脚为中断输入，边沿触发// 0-->none, 1-->rising, 2-->falling, 3-->bothstatic int gpio_edge(int pin, int edge){const char dir_str[] = "none\0rising\0falling\0both"; char ptr;char path[64]; int fd; switch(edge){case 0:ptr = 0;break;case 1:ptr = 5;break;case 2:ptr = 12;break;case 3:ptr = 20;break;default:ptr = 0;} snprintf(path, sizeof(path), "/sys/class/gpio/gpio%d/edge", pin); fd = open(path, O_WRONLY); if (fdMSG("Failed to open gpio edge for writing!\n"); return -1; } if (write(fd, &dir_str[ptr], strlen(&dir_str[ptr]))MSG("Failed to set edge!\n"); return -1; } close(fd); return 0; }//GPIO1_17int main() { int gpio_fd, ret;struct pollfd fds[1];char buff[10];unsigned char cnt = 0;//LED引脚初始化gpio_export(115);gpio_direction(115, 1);gpio_write(115, 0);//按键引脚初始化gpio_export(49);gpio_direction(49, 0);gpio_edge(49,1);gpio_fd = open("/sys/class/gpio/gpio49/value",O_RDONLY);if(gpio_fdMSG("Failed to open value!\n"); return -1; }fds[0].fd = gpio_fd;fds[0].events = POLLPRI;ret = read(gpio_fd,buff,10);if( ret == -1 )MSG("read\n");while(1){ret = poll(fds,1,0);if( ret == -1 )MSG("poll\n");if( fds[0].revents & POLLPRI){ret = lseek(gpio_fd,0,SEEK_SET);if( ret == -1 )MSG("lseek\n");ret = read(gpio_fd,buff,10);if( ret == -1 )MSG("read\n");gpio_write(115, cnt++%2);}usleep(100000);}return 0;}