at24c08 E2PROM的I2C设备驱动实例——基于mini2440
AT24C08提供8192位的串行电可擦写可编程只读存储器(EEPROM)，
16字节页写模式。
内核版本：2.6.32。
实验所用开发板mini2440。
第一步：在arch/arm/mach-s3c2440/mach-mini2440.c添加E2PROM的板级信息
1、添加头文件：
#include
#include
2、添加平台板级信息
static struct at24_platform_data at24_platdata = { .byte_len = 8192,//字节大小 .page_size = 16,//页数大小};static struct i2c_board_info mini2440_i2c_devices[] = { { I2C_BOARD_INFO("24c08",0x50),//第一个参数是硬件名称，驱动的名字匹配不上的时候，会和这个匹配，第二个参数是IIC硬件地址。 .platform_data = &at24_platdata, }};
3、在mini2440_machine_init(void)函数中添加
i2c_register_board_info(0,mini2440_i2c_devices,ARRAY_SIZE(mini2440_i2c_devices));//注册板级信息
4、编译内核并重新烧写开发板的zImage
make zImage
第二步：编写驱动代码
#include#include#include#include#include#include#include#define E2PROM_MAJOR 250//可以通过cat /proc/devices查看哪些设备号没有被使用MODULE_LICENSE("GPL");struct e2prom_device{ struct i2c_client *at24c02_client; struct class *at24c02_class; struct device *at24c02_device;};struct e2prom_device *e2prom_dev;struct i2c_device_id e2prom_table[]={ [0]={ .name ="24c02", .driver_data =0, }, [1]={ .name ="24c08", .driver_data =0, },};static int i2c_read_byte(char *buf,int count){ int ret=0; struct i2c_msg msg; msg.addr =e2prom_dev->at24c02_client->addr;//0x05 msg.flags =1;//1 代表读 0 代表写 msg.len =count; msg.buf =buf; ret=i2c_transfer(e2prom_dev->at24c02_client->adapter,&msg,1); if(ret<0){ printk("i2c transfer failed!\n"); return -EINVAL; } return ret;}static int i2c_write_byte(char *buf,int count){ int ret=0; struct i2c_msg msg; msg.addr =e2prom_dev->at24c02_client->addr;//0x05 msg.flags =0; //写 msg.len =count; msg.buf =buf; ret=i2c_transfer(e2prom_dev->at24c02_client->adapter,&msg,1); if(ret<0){ printk("i2c transfer failed!\n"); return -EINVAL; } return ret;}static int e2prom_open(struct inode *inode, struct file *file){ return 0;}static size_t e2prom_read(struct file *filep, char __user *buf, size_t size, loff_t *ppos){ int ret = 0; char *tmp; tmp = kmalloc(size,GFP_KERNEL); if(tmp==NULL){ printk("malloc failed!\n"); return -ENOMEM; } ret = i2c_read_byte(tmp,size); if(ret<0){ printk("read byte failed!\n"); ret = -EINVAL; goto err0; } ret = copy_to_user(buf,tmp,size); if(ret){ printk("copy data failed!\n"); ret =-EINVAL; goto err0; } kfree(tmp); return size; err0: kfree(tmp); return ret; }static ssize_t e2prom_write(struct file *filep, const char __user *buf, size_t size, loff_t *ppos){ int ret = 0; char *tmp; tmp = kmalloc(size,GFP_KERNEL); if(tmp == NULL){ printk("malloc failed!\n"); return -ENOMEM; goto err0; } ret = copy_from_user(tmp,buf,size); if(ret){ printk("copy data failed!\n"); ret =-EFAULT; goto err0; } ret = i2c_write_byte(tmp,size); if(ret<0){ printk("write byte failed!\n"); ret = -EINVAL; goto err0; } kfree(tmp); return size; err0: kfree(tmp); return ret;}struct file_operations e2prom_fops = { .owner =THIS_MODULE, .open =e2prom_open, .read =e2prom_read, .write =e2prom_write,};static int e2prom_probe(struct i2c_client *client, const struct i2c_device_id *id){ int ret; printk("enter probe!\n"); e2prom_dev = kmalloc(sizeof(struct e2prom_device),GFP_KERNEL); if(e2prom_dev == NULL){ printk("malloc failed\n"); return -ENOMEM; } e2prom_dev->at24c02_client = client; /*给用户提供接口*/ ret = register_chrdev(E2PROM_MAJOR,"e2prom_module",&e2prom_fops); if(ret < 0) { printk("register major failded\n"); ret =-EINVAL; goto err0; } /*创建设备类*/ e2prom_dev->at24c02_class = class_create(THIS_MODULE,"e2prom_class"); if(IS_ERR(e2prom_dev->at24c02_class)){ printk("class create failed\n"); ret =PTR_ERR(e2prom_dev->at24c02_client); goto err1; } /*创建设备文件*/ e2prom_dev->at24c02_device=device_create(e2prom_dev->at24c02_class,NULL,MKDEV(E2PROM_MAJOR,0),NULL,"at24c08"); if(IS_ERR(e2prom_dev->at24c02_device)){ printk("class create failed\n"); ret =PTR_ERR(e2prom_dev->at24c02_device); goto err1; } return 0; err1: unregister_chrdev(E2PROM_MAJOR,"e2prom_module"); err0: kfree(e2prom_dev); return ret;}static int e2prom_remove(struct i2c_client *client){ unregister_chrdev(E2PROM_MAJOR,"e2prom_module"); device_destroy(e2prom_dev->at24c02_class, MKDEV(E2PROM_MAJOR,0)); class_destroy(e2prom_dev->at24c02_class); kfree(e2prom_dev); return 0; }/*构建一个struct i2c_driver结构体*/static struct i2c_driver e2prom_driver={ .probe =e2prom_probe, .remove =e2prom_remove, .id_table =e2prom_table,//记录此驱动服务于哪些设备 .driver ={ .name ="e2prom",// },};static int __init e2prom_init(void){ /*注册平台特定驱动 *1)将i2c驱动加入i2c总线的驱动链表 *2)搜索i2c总线的设备链表，每搜索一个都会调用i2c总线的match * 实现client->name与id->name进行匹配，匹配成功就会调用 * i2c驱动中的probe函数 */ i2c_add_driver(&e2prom_driver); return 0;}static void __exit e2prom_exit(void){ i2c_del_driver(&e2prom_driver);}module_init(e2prom_init);module_exit(e2prom_exit);
第三步：编写测试程序
读写的操作方式采用Byte Write方式读，和Random Read方式写。
其中
Random Read方式需要对写入的地址进行确认。也就是读操作的时候，需要写一次，再读一次。具体步骤如下图所示：
#include #include #include #include #include #include #include #include /* ./i2c_test w data ./i2c_test r */int main(int argc,char **argv){ int fd; char register_addr = 0x78;//要写入的地址 char wbuf[2];//写缓冲区 char rbuf[2];//读缓冲区 //打开设备 fd = open("/dev/at24c08", O_RDWR); if (fd < 0) { perror("open error\n"); exit(1); } if(strcmp(argv[1],"w") == 0) {//写操作 Byte Write wbuf[0] = register_addr; wbuf[1] = atoi(argv[2]); /向register_addr地址中写入数据，因为设备地址已经在板级信息中确定了，所以不需要通过ioctl设置设备地址*/ if(res = write(fd, wbuf, 2) != 2) { perror("write error\n"); exit(1); }- }
else {//读操作 Random Read if(write(fd, ®ister_addr, 1) != 1) //验证是否从register_addr地址读出 { perror("write error\n"); exit(1); } if(read(fd, &rbuf, 1) != 1) { perror("read error\n"); exit(1); } else { printf("rbuf[0] = %d\n",rbuf[0]); } - }
return 0;}
第四步：验证结果
测试成功！