对于读，通常是按照下面的时序
MaterSI2CAddr+WriteBit InternalRegisterAddr SI2CAddr+ReadBit ACK NACKPSlave ACK ACK ACK DATA DATA
i2c子系统为了实现这种通信方法，为我们封装了i2c_msg结构，对于每一个START信号，都对应一个i2c_msg对象，实际操作中我们会将所有的请求封装成一个struct i2c_msg[]，一次性将所有的请求通过i2c_transfer()发送给匹配到的client的从属的adapter，由adapter根据相应的algo域以及master_xfer域通过主机驱动来将这些请求发送给硬件上的设备
实例这是一个通过i2c总线来访问mpu6050的驱动
//mpu6050_common.h #define MPU6050_MAGIC 'K' union mpu6050_data { struct { short x; short y; short z; }accel; struct { short x; short y; short z; }gyro; unsigned short temp; }; #define GET_ACCEL _IOR(MPU6050_MAGIC, 0, union mpu6050_data) #define GET_GYRO _IOR(MPU6050_MAGIC, 1, union mpu6050_data) #define GET_TEMP _IOR(MPU6050_MAGIC, 2, union mpu6050_data) //mpu6050_drv.h #define SMPLRT_DIV 0x19 //陀螺仪采样率，典型值：0x07(125Hz) #define CONFIG 0x1A //低通滤波频率，典型值：0x06(5Hz) #define GYRO_CONFIG 0x1B //陀螺仪自检及测量范围，典型值：0x18(不自检，2000deg/s) #define ACCEL_CONFIG 0x1C //加速计自检、测量范围及高通滤波，典型值：0x18(不自检，2G，5Hz) #define ACCEL_XOUT_H 0x3B #define ACCEL_XOUT_L 0x3C #define ACCEL_YOUT_H 0x3D #define ACCEL_YOUT_L 0x3E #define ACCEL_ZOUT_H 0x3F #define ACCEL_ZOUT_L 0x40 #define TEMP_OUT_H 0x41 #define TEMP_OUT_L 0x42 #define GYRO_XOUT_H 0x43 #define GYRO_XOUT_L 0x44 #define GYRO_YOUT_H 0x45 #define GYRO_YOUT_L 0x46 #define GYRO_ZOUT_H 0x47 //陀螺仪z轴角速度数据寄存器（高位） #define GYRO_ZOUT_L 0x48 //陀螺仪z轴角速度数据寄存器（低位） #define PWR_MGMT_1 0x6B //电源管理，典型值：0x00(正常启用) #define WHO_AM_I 0x75 //IIC地址寄存器(默认数值0x68，只读) #define SlaveAddress 0x68 //MPU6050-I2C地址寄存器 #define W_FLG 0 #define R_FLG 1 //mpu6050.c struct mpu6050_pri { struct cdev dev; struct i2c_client *client; }; struct mpu6050_pri dev; static void mpu6050_write_byte(struct i2c_client *client,const unsigned char reg,const unsigned char val) { char txbuf[2] = {reg,val}; struct i2c_msg msg[2] = { [0] = { .addr = client->addr, .flags= W_FLG, .len = sizeof(txbuf), .buf = txbuf, }, }; i2c_transfer(client->adapter, msg, ARRAY_SIZE(msg)); } static char mpu6050_read_byte(struct i2c_client *client,const unsigned char reg) { char txbuf[1] = {reg}; char rxbuf[1] = {0}; struct i2c_msg msg[2] = { [0] = { .addr = client->addr, .flags = W_FLG, .len = sizeof(txbuf), .buf = txbuf, }, [1] = { .addr = client->addr, .flags = I2C_M_RD, .len = sizeof(rxbuf), .buf = rxbuf, }, }; i2c_transfer(client->adapter, msg, ARRAY_SIZE(msg)); return rxbuf[0]; } static int dev_open(struct inode *ip, struct file *fp) { return 0; } static int dev_release(struct inode *ip, struct file *fp) { return 0; } static long dev_ioctl(struct file *fp, unsigned int cmd, unsigned long arg) { int res = 0; union mpu6050_data data = {{0}}; switch(cmd){ case GET_ACCEL: data.accel.x = mpu6050_read_byte(dev.client,ACCEL_XOUT_L); data.accel.x|= mpu6050_read_byte(dev.client,ACCEL_XOUT_H)<<8; data.accel.y = mpu6050_read_byte(dev.client,ACCEL_YOUT_L); data.accel.y|= mpu6050_read_byte(dev.client,ACCEL_YOUT_H)<<8; data.accel.z = mpu6050_read_byte(dev.client,ACCEL_ZOUT_L); data.accel.z|= mpu6050_read_byte(dev.client,ACCEL_ZOUT_H)<<8; break; case GET_GYRO: data.gyro.x = mpu6050_read_byte(dev.client,GYRO_XOUT_L); data.gyro.x|= mpu6050_read_byte(dev.client,GYRO_XOUT_H)<<8; data.gyro.y = mpu6050_read_byte(dev.client,GYRO_YOUT_L); data.gyro.y|= mpu6050_read_byte(dev.client,GYRO_YOUT_H)<<8; data.gyro.z = mpu6050_read_byte(dev.client,GYRO_ZOUT_L); data.gyro.z|= mpu6050_read_byte(dev.client,GYRO_ZOUT_H)<<8; printk("gyro:x %d, y:%d, z:%d\n",data.gyro.x,data.gyro.y,data.gyro.z); break; case GET_TEMP: data.temp = mpu6050_read_byte(dev.client,TEMP_OUT_L); data.temp|= mpu6050_read_byte(dev.client,TEMP_OUT_H)<<8; printk("temp: %d\n",data.temp); break; default: printk(KERN_INFO "invalid cmd"); break; } printk("acc:x %d, y:%d, z:%d\n",data.accel.x,data.accel.y,data.accel.z); res = copy_to_user((void *)arg,&data,sizeof(data)); return sizeof(data); } struct file_operations fops = { .open = dev_open, .release = dev_release, .unlocked_ioctl = dev_ioctl, }; #define DEV_CNT 1 #define DEV_MI 0 #define DEV_MAME "mpu6050" struct class *cls; dev_t dev_no ; static void mpu6050_init(struct i2c_client *client) { mpu6050_write_byte(client, PWR_MGMT_1, 0x00); mpu6050_write_byte(client, SMPLRT_DIV, 0x07); mpu6050_write_byte(client, CONFIG, 0x06); mpu6050_write_byte(client, GYRO_CONFIG, 0x18); mpu6050_write_byte(client, ACCEL_CONFIG, 0x0); } static int mpu6050_probe(struct i2c_client * client, const struct i2c_device_id * id) { dev.client = client; printk(KERN_INFO "xj_match ok\n"); cdev_init(&dev.dev,&fops); alloc_chrdev_region(&dev_no,DEV_MI,DEV_CNT,DEV_MAME); cdev_add(&dev.dev,dev_no,DEV_CNT); mpu6050_init(client); /*自动创建设备文件*/ cls = class_create(THIS_MODULE,DEV_MAME); device_create(cls,NULL,dev_no,NULL,"%s%d",DEV_MAME,DEV_MI); printk(KERN_INFO "probe\n"); return 0; } static int mpu6050_remove(struct i2c_client * client) { device_destroy(cls,dev_no); class_destroy(cls); unregister_chrdev_region(dev_no,DEV_CNT); return 0; } struct of_device_id mpu6050_dt_match[] = { {.compatible = "invensense,mpu6050"}, {}, }; struct i2c_device_id mpu6050_dev_match[] = {}; struct i2c_driver mpu6050_driver = { .probe = mpu6050_probe, .remove = mpu6050_remove, .driver = { .owner = THIS_MODULE, .name = "mpu6050drv", .of_match_table = of_match_ptr(mpu6050_dt_match), }, .id_table = mpu6050_dev_match, }; module_i2c_driver(mpu6050_driver); MODULE_LICENSE("GPL");