1. Linux内核支持I2C通用设备驱动（用户态驱动：由应用层实现对硬件的控制可以称之为用户态驱动），实现文件位于drivers/i2c/i2c-dev.c，设备文件为/dev/i2c-0
2. I2C通用设备驱动以字符设备注册进内核的
static const struct file_operations i2cdev_fops = {
.owner = THIS_MODULE,
.llseek = no_llseek,
.read = i2cdev_read,
.write = i2cdev_write,
.unlocked_ioctl = i2cdev_ioctl,
.open = i2cdev_open,
.release = i2cdev_release,
};
res = register_chrdev(I2C_MAJOR, "i2c", &i2cdev_fops);
3. 对设备文件进行读写时，可以调用read、write或者ioctl等方法，他们都是通过调用函数i2c_transfer来实现对I2C设备的操作的
int i2c_transfer(struct i2c_adapter * adap, struct i2c_msg *msgs, int num)
{
int ret; /* REVISIT the fault reporting model here is weak:
*
* - When we get an error after receiving N bytes from a slave,
* there is no way to report "N".
*
* - When we get a NAK after transmitting N bytes to a slave,
* there is no way to report "N" ... or to let the master
* continue executing the rest of this combined message, if
* that's the appropriate response.
*
* - When for example "num" is two and we successfully complete
* the first message but get an error part way through the
* second, it's unclear whether that should be reported as
* one (discarding status on the second message) or errno
* (discarding status on the first one).
*/ if (adap->algo->master_xfer) {
#ifdef DEBUG
for (ret = ; ret < num; ret++) {
dev_dbg(&adap->dev, "master_xfer[%d] %c, addr=0x%02x, "
"len=%d%s\n", ret, (msgs[ret].flags & I2C_M_RD)
? 'R' : 'W', msgs[ret].addr, msgs[ret].len,
(msgs[ret].flags & I2C_M_RECV_LEN) ? "+" : "");
}
#endif if (in_atomic() || irqs_disabled()) {
ret = mutex_trylock(&adap->bus_lock);
if (!ret)
/* I2C activity is ongoing. */
return -EAGAIN;
} else {
mutex_lock_nested(&adap->bus_lock, adap->level);
} ret = adap->algo->master_xfer(adap,msgs,num);
mutex_unlock(&adap->bus_lock); return ret;
} else {
dev_dbg(&adap->dev, "I2C level transfers not supported\n");
return -EOPNOTSUPP;
}
}
4. i2c_transfer通过代码可以看出，i2c_transfer 通过调用相应的 adapter 的 master_xfer 方法实现的，而 master_xfer 主要是根据 struct i2c_msg 类型的msgs来进行处理的。
struct i2c_msg {
__u16 addr; /* slave address */
__u16 flags;
#define I2C_M_TEN 0x0010 /* this is a ten bit chip address */
#define I2C_M_RD 0x0001 /* read data, from slave to master */
#define I2C_M_NOSTART 0x4000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_REV_DIR_ADDR 0x2000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_IGNORE_NAK 0x1000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_NO_RD_ACK 0x0800 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_RECV_LEN 0x0400 /* length will be first received byte */
__u16 len; /* msg length */
__u8 *buf; /* pointer to msg data */
};
5. I2C用户态驱动简单示例
（1）通过read、write实现对I2C设备的操作
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <malloc.h>
#include <sys/ioctl.h>
#include <string.h>
#include <linux/i2c.h>
#include <linux/i2c-dev.h> #define SLAVE_ADDRESS 0x50
#define I2C_WRITE_FLAG 0x00
#define I2C_READ_FLAG 0x01 #define USAGE "xxx -r address length\nxxx -w address data1 data2...\n" void i2c_write_bytes(int fd, unsigned char address, unsigned char* data, unsigned short len)
{
unsigned char* write_data = malloc(len + ); write_data[] = address;
memcpy(&write_data[], data, len); ioctl(fd, I2C_SLAVE, SLAVE_ADDRESS);
ioctl(fd, I2C_TIMEOUT, );
ioctl(fd, I2C_RETRIES, ); write(fd, write_data, len + ); printf("Write data success\n"); if(write_data != NULL)
{
free(write_data);
write_data = NULL;
}
} void i2c_read_bytes(int fd, unsigned char address, unsigned char* buf, unsigned short len)
{
ioctl(fd, I2C_SLAVE, SLAVE_ADDRESS);
ioctl(fd, I2C_TIMEOUT, );
ioctl(fd, I2C_RETRIES, ); write(fd, &address, ); read(fd, buf, len); printf("buf[0] = 0x%x\n", buf[]); printf("Read data success\n");
} int main(int argc, char* argv[])
{
int opt;
int fd = -; unsigned char address;
unsigned short len = , i = ;
unsigned char buf[] = {}; // Open device file
fd = open("/dev/i2c-0", O_RDWR);
if(fd < )
{
printf("Open file error\n");
goto Exit;
} while((opt = getopt(argc, argv, "w:r:")) != -)
{
switch(opt)
{
case 'w':
printf("optarg = %s\n", optarg);
printf("optind = %d\n", optind);
printf("argc = %d\n", argc);
printf("argv[optind] = %s\n", argv[optind]); address = (unsigned char)strtol(optarg, NULL, );
printf("address = %x\n", address); for(len = ; optind < argc; optind++, len++)
{
buf[len] = (unsigned char)strtol(argv[optind], NULL, );
} printf("len = %x\n", len); i2c_write_bytes(fd, address, buf, len); break; case 'r':
printf("optarg = %s\n", optarg);
printf("optind = %d\n", optind);
printf("argv[optind] = %s\n", argv[optind]); address = (unsigned char)strtol(optarg, NULL, );
printf("address = 0x%x\n", address); len = (unsigned short)strtol(argv[optind], NULL, );
printf("len = 0x%x\n", len); i2c_read_bytes(fd, address, buf, len); printf("Read content:\n");
for(i = ; i < len; i++)
{
printf("0x%x ", buf[i]);
}
printf("\n");
break; default:
printf("Invalid parameter\n");
printf(USAGE);
break;
}
} Exit:
close(fd); return ;
}
（2）通过ioctl实现对I2C设备的操作
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <malloc.h>
#include <sys/ioctl.h>
#include <string.h>
#include <linux/i2c.h>
#include <linux/i2c-dev.h> #define SLAVE_ADDRESS 0x50
#define I2C_WRITE_FLAG 0x00
#define I2C_READ_FLAG 0x01 #define USAGE "xxx -r address length\nxxx -w address data1 data2...\n" void i2c_write_bytes(int fd, unsigned char address, unsigned char* data, unsigned short len)
{
struct i2c_rdwr_ioctl_data e2prom_write_data; e2prom_write_data.nmsgs = ;
e2prom_write_data.msgs = malloc(sizeof(struct i2c_msg) * e2prom_write_data.nmsgs); e2prom_write_data.msgs[].addr = SLAVE_ADDRESS;
e2prom_write_data.msgs[].flags = I2C_WRITE_FLAG;
e2prom_write_data.msgs[].len = len + ;//address data
e2prom_write_data.msgs[].buf = malloc(e2prom_write_data.msgs[].len); e2prom_write_data.msgs[].buf[] = address; memcpy(&(e2prom_write_data.msgs[].buf[]), data, (size_t)len); // Using ioctl to write data
ioctl(fd, I2C_RDWR, (unsigned long)&e2prom_write_data); printf("Write data success\n"); if(e2prom_write_data.msgs != NULL)
{
free(e2prom_write_data.msgs);
e2prom_write_data.msgs = NULL;
}
} void i2c_read_bytes(int fd, unsigned char address, unsigned char* buf, unsigned short len)
{
struct i2c_rdwr_ioctl_data e2prom_read_data; e2prom_read_data.nmsgs = ;//Need writing address first, then reading
e2prom_read_data.msgs = malloc(sizeof(struct i2c_msg) * e2prom_read_data.nmsgs); e2prom_read_data.msgs[].addr = SLAVE_ADDRESS;
e2prom_read_data.msgs[].flags = I2C_WRITE_FLAG;
e2prom_read_data.msgs[].len = ;
e2prom_read_data.msgs[].buf = malloc(e2prom_read_data.msgs[].len); e2prom_read_data.msgs[].buf[] = address; e2prom_read_data.msgs[].addr = SLAVE_ADDRESS;
e2prom_read_data.msgs[].flags = I2C_READ_FLAG;
e2prom_read_data.msgs[].len = len;
e2prom_read_data.msgs[].buf = malloc(e2prom_read_data.msgs[].len);
e2prom_read_data.msgs[].buf[] = 0x00; // Using ioctl to read data
ioctl(fd, I2C_RDWR, (unsigned long)&e2prom_read_data); printf("e2prom_read_data.msgs[1].buf[0] = 0x%x\n", e2prom_read_data.msgs[].buf[]); memcpy((void*)buf, (void*)(e2prom_read_data.msgs[].buf), (unsigned int)len); if(e2prom_read_data.msgs != NULL)
{
free(e2prom_read_data.msgs);
e2prom_read_data.msgs = NULL;
}
} int main(int argc, char* argv[])
{
int opt;
int fd = -; unsigned char address;
unsigned short len = , i = ;
unsigned char buf[] = {}; // Open device file
fd = open("/dev/i2c-0", O_RDWR);
if(fd < )
{
printf("Open file error\n");
goto Exit;
} while((opt = getopt(argc, argv, "w:r:")) != -)
{
switch(opt)
{
case 'w':
printf("optarg = %s\n", optarg);
printf("optind = %d\n", optind);
printf("argc = %d\n", argc);
printf("argv[optind] = %s\n", argv[optind]); address = (unsigned char)strtol(optarg, NULL, );
printf("address = %x\n", address); for(len = ; optind < argc; optind++,len++)
{
buf[len] = (unsigned char)strtol(argv[optind], NULL, );
} printf("len = %x\n", len); i2c_write_bytes(fd, address, buf, len); break; case 'r':
printf("optarg = %s\n", optarg);
printf("optind = %d\n", optind);
printf("argv[optind] = %s\n", argv[optind]); address = (unsigned char)strtol(optarg, NULL, );
printf("address = 0x%x\n", address); len = (unsigned short)strtol(argv[optind], NULL, );
printf("len = 0x%x\n", len); i2c_read_bytes(fd, address, buf, len); printf("Read content:\n");
for(i = ; i < len; i++)
{
printf("0x%x ", buf[i]);
}
printf("\n");
break; default:
printf("Invalid parameter\n");
printf(USAGE);
break;
}
} Exit:
close(fd); return ;
}