linux之I2C驱动程序
韦老师的笔记，供自己以后学习
linux内核i2c分析思路：
怎么写I2C设备驱动程序？
1. 分配一个i2c_driver结构体
2. 设置
attach_adapter // 它直接调用 i2c_probe(adap, 设备地址, 发现这个设备后要调用的函数);
detach_client // 卸载这个驱动后,如果之前发现能够支持的设备,则调用它来清理
3. 注册：i2c_add_driver
测试1th:
1. insmod at24cxx.ko
观察输出信息
2. 修改normal_addr里的0x50为0x60
编译加载，观察输出信息
驱动程序源码：
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/jiffies.h>
#include <linux/i2c.h>
#include <linux/mutex.h>
#include <linux/fs.h>
#include <asm/uaccess.h>
static unsigned short ignore[] = { I2C_CLIENT_END };
static unsigned short normal_addr[] = { 0x50, I2C_CLIENT_END }; /* 地址值是7位 */
/* 改为0x60的话, 由于不存在设备地址为0x60的设备, 所以at24cxx_detect不被调用 */
static unsigned short force_addr[] = {ANY_I2C_BUS, 0x60, I2C_CLIENT_END};
static unsigned short * forces[] = {force_addr, NULL};
static struct i2c_client_address_data addr_data = {
.normal_i2c = normal_addr, /* 要发出S信号和设备地址并得到ACK信号,才能确定存在这个设备 */
.probe = ignore,
.ignore = ignore,
//.forces = forces, /* 强制认为存在这个设备 */
};
static struct i2c_driver at24cxx_driver;
static int major;
static struct class *cls;
struct i2c_client *at24cxx_client;
static ssize_t at24cxx_read(struct file *file, char __user *buf, size_t size, loff_t * offset)
{
unsigned char address;
unsigned char data;
struct i2c_msg msg[2];
int ret;
/* address = buf[0]
* data = buf[1]
*/
if (size != 1)
return -EINVAL;
copy_from_user(&address, buf, 1);
/* 数据传输三要素: 源,目的,长度 */
/* 读AT24CXX时,要先把要读的存储空间的地址发给它 */
msg[0].addr = at24cxx_client->addr; /* 目的 */
msg[0].buf = &address; /* 源 */
msg[0].len = 1; /* 地址=1 byte */
msg[0].flags = 0; /* 表示写 */
/* 然后启动读操作 */
msg[1].addr = at24cxx_client->addr; /* 源 */
msg[1].buf = &data; /* 目的 */
msg[1].len = 1; /* 数据=1 byte */
msg[1].flags = I2C_M_RD; /* 表示读 */
ret = i2c_transfer(at24cxx_client->adapter, msg, 2);
if (ret == 2)
{
copy_to_user(buf, &data, 1);
return 1;
}
else
return -EIO;
}
static ssize_t at24cxx_write(struct file *file, const char __user *buf, size_t size, loff_t *offset)
{
unsigned char val[2];
struct i2c_msg msg[1];
int ret;
/* address = buf[0]
* data = buf[1]
*/
if (size != 2)
return -EINVAL;
copy_from_user(val, buf, 2);
/* 数据传输三要素: 源,目的,长度 */
msg[0].addr = at24cxx_client->addr; /* 目的 */
msg[0].buf = val; /* 源 */
msg[0].len = 2; /* 地址+数据=2 byte */
msg[0].flags = 0; /* 表示写 */
ret = i2c_transfer(at24cxx_client->adapter, msg, 1);
if (ret == 1)
return 2;
else
return -EIO;
}
static struct file_operations at24cxx_fops = {
.owner = THIS_MODULE,
.read = at24cxx_read,
.write = at24cxx_write,
};
static int at24cxx_detect(struct i2c_adapter *adapter, int address, int kind)
{
printk("at24cxx_detect\n");
/* 构构一个i2c_client结构体: 以后收改数据时会用到它 */
at24cxx_client = kzalloc(sizeof(struct i2c_client), GFP_KERNEL);
at24cxx_client->addr = address;
at24cxx_client->adapter = adapter;
at24cxx_client->driver = &at24cxx_driver;
strcpy(at24cxx_client->name, "at24cxx");
i2c_attach_client(at24cxx_client);
major = register_chrdev(0, "at24cxx", &at24cxx_fops);
cls = class_create(THIS_MODULE, "at24cxx");
class_device_create(cls, NULL, MKDEV(major, 0), NULL, "at24cxx"); /* /dev/at24cxx */
return 0;
}
static int at24cxx_attach(struct i2c_adapter *adapter)
{
return i2c_probe(adapter, &addr_data, at24cxx_detect);
}
static int at24cxx_detach(struct i2c_client *client)
{
printk("at24cxx_detach\n");
class_device_destroy(cls, MKDEV(major, 0));
class_destroy(cls);
unregister_chrdev(major, "at24cxx");
i2c_detach_client(client);
kfree(i2c_get_clientdata(client));
return 0;
}
/* 1. 分配一个i2c_driver结构体 */
/* 2. 设置i2c_driver结构体 */
static struct i2c_driver at24cxx_driver = {
.driver = {
.name = "at24cxx",
},
.attach_adapter = at24cxx_attach,
.detach_client = at24cxx_detach,
};
static int at24cxx_init(void)
{
i2c_add_driver(&at24cxx_driver);
return 0;
}
static void at24cxx_exit(void)
{
i2c_del_driver(&at24cxx_driver);
}
module_init(at24cxx_init);
module_exit(at24cxx_exit);
MODULE_LICENSE("GPL");
应用测试程序：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
/* i2c_test r addr
* i2c_test w addr val
*/
void print_usage(char *file)
{
printf("%s r addr\n", file);
printf("%s w addr val\n", file);
}
int main(int argc, char **argv)
{
int fd;
unsigned char buf[2];
if ((argc != 3) && (argc != 4))
{
print_usage(argv[0]);
return -1;
}
fd = open("/dev/at24cxx", O_RDWR);
if (fd < 0)
{
printf("can't open /dev/at24cxx\n");
return -1;
}
if (strcmp(argv[1], "r") == 0)
{
buf[0] = strtoul(argv[2], NULL, 0);
read(fd, buf, 1);
printf("data: %c, %d, 0x%2x\n", buf[0], buf[0], buf[0]);
}
else if (strcmp(argv[1], "w") == 0)
{
buf[0] = strtoul(argv[2], NULL, 0);
buf[1] = strtoul(argv[3], NULL, 0);
write(fd, buf, 2);
}
else
{
print_usage(argv[0]);
return -1;
}
return 0;
}