(20) Use of the Ioctl,write,read function of I²c in Linux

First, the use of the IOCTL function:
Prototype: struct ioctl(struct file *file,unsigned int cmd,unsigned long arg);
CMD has i2c_slave,i2c_slave_force,i2c_tenbit,i2c_s3c2410_set_speed several options;
I2c_slave: The corresponding arg value is the i²c slave address, used to set the i²c slave address;

I2c_slave_force: The corresponding arg value is the i²c slave address, which is used to modify the address of the i²c slave machine;

I2c_tenbit: The corresponding arg value is 0: The slave address is 7 bit, and the corresponding ARG value is 1: The slave address is 10bit. The number of digits used to specify the address of the i²c slave;

I2c_s3c2410_set_speed: The corresponding arg value is the crossover value of the I²C bus controller. Used to set the I²C bus controller clock frequency;
　

Common settings set the I²c slave address is 0xa0, if you choose the AT24C08 device, then the slave is a 7 bit address, so to move right 1 bits, specify the slave address is 7 bit,

IOCTL (fd,i2c_tenbit,0).
IOCTL (fd,i2c_slave,0xa0>>1);

Use of the Read () and write() functions
Assuming a sub-address of 12, write 7 bytes to the device with the child address:

unsigned char buf[8]={12, ' s ', ' j ', ' s ', ' u ', ' n ', ' n ', ' Y ');write (fd,buf,9);/* writes in 7 bytes, 1th byte is a sub-address */

Read 7 bytes from an I²C device with a sub-address:
unsigned char suba=0;recbuf[20];
Write (fd,buf,1);/* Send sub-address 0*/
Read (fd,recbuf,7);/* Start reading 7 bytes from sub-address 12 */

Ii. The difference between the IOCTL and read and write :

Known as the "Swiss Army Knife" of the UNIX system, the IOCTL was used as an extension of the Linux system
It can be used widely in Linux system by a common method.

IOCTL is typically used to transfer control between user-space programs and driver modules
The difference between theIOCTL and read and write is:
1, theIOCTL is generally used to transmit control parameters, such as: Serial port baud rate, serial port flow control method (Xon/xoff, DTR/DSR, rts/cts), etc., generally do not
Used to pass "primary" data (I don't have the right words to explain:).

2, theioctl semantics is generally non-blocking, read and write but the province is blocked.

3, theIOCTL interface is omnipotent,ioctl(FD, CMD, arg) The third parameter can be an integer variable, or a pointer to a data structure.

(20) Use of the Ioctl,write,read function of I²c in Linux