27.3.4.2 I2C driver in kernel (II)

Direct access to user mode, kernel drivers using
dev-interface




Note, do not directly use the read (), write () operation function, directly i2c_smbus_write_word_data, i2c_smbus_read_word_data. The official document to the description, the following

drivers are compiled into the kernel to be effective, I2c-dev.c those dependent on configuration items, see Makefile

makemenuconfig, search CONFIG_I2C_CHARDEV

Reboot the kernel, compile a new kernel, and then downloaded to the development board



test code

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "i2c-dev.h"


/* i2c_usr_test </dev/i2c-0> <dev_addr> r addr
 * i2c_usr_test </dev/i2c-0> <dev_addr> w addr val
 */

void print_usage(char *file)
{
	printf("%s </dev/i2c-0> <dev_addr> r addr\n", file);
	printf("%s </dev/i2c-0> <dev_addr> w addr val\n", file);
}

int main(int argc, char **argv)
{
	int fd;
	unsigned char addr, data;
	int dev_addr;
	
	if ((argc != 5) && (argc != 6))
	{
		print_usage(argv[0]);
		return -1;
	}

	fd = open(argv[1], O_RDWR);
	if (fd < 0)
	{
		printf("can't open %s\n", argv[1]);
		return -1;
	}

	dev_addr = strtoul(argv[2], NULL, 0);
	if (ioctl(fd, I2C_SLAVE, dev_addr) < 0)
	{    
		/* ERROR HANDLING; you can check errno to see what went wrong */    
		printf("set addr error!\n");
		return -1;
	}

	if (strcmp(argv[3], "r") == 0)
	{
		addr = strtoul(argv[4], NULL, 0);
		
		data = i2c_smbus_read_word_data(fd, addr);
			
		printf("data: %c, %d, 0x%2x\n", data, data, data);
	}
	else if ((strcmp(argv[3], "w") == 0) && (argc == 6))
	{
		addr = strtoul(argv[4], NULL, 0);
		data = strtoul(argv[5], NULL, 0);
		i2c_smbus_write_byte_data(fd, addr, data);		
	}
	else
	{
		print_usage(argv[0]);
		return -1;
	}
	
	return 0;
}