Petaflot at 11:05, 5 November 2011

2011-11-05T11:05:47Z

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2011-11-02T22:18:24Z

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← Older revision		Revision as of 11:05, 5 November 2011
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		+	Nico found this post on the PCEngines forum: [http://www.pcengines.info/forums/?page=post&id=DE352734-3123-41F2-AFA4-0CD1939BFDC7&fid=40251191-FF24-48A8-BB0E-995B04812ADE I2C-bus examples or a howto]

		+	== Working example ==
		+	The above helps, but it's not all. Looking at kernel Documentation/i2c/dev-interface helps some more, but not quite. Here's the smallest compiling example to use I²C in userspace linux ; it took me a while to get it together.

−	~~http:~~//~~www~~.~~pcengines~~.~~info~~/~~forums~~/~~?page=post&id=DE352734~~-~~3123~~-~~41F2~~-~~AFA4~~-~~0CD1939BFDC7&fid~~=~~40251191~~-~~FF24~~-~~48A8-BB0E-995B04812ADE~~	+	;example from from Documentation/i2c/dev-interface:
		+
		+	So let's say you want to access an i2c adapter from a C program. The
		+	first thing to do is "#include <linux/i2c-dev.h>". Please note that
		+	there are two files named "i2c-dev.h" out there, one is distributed
		+	with the Linux kernel and is meant to be included from kernel
		+	driver code, the other one is distributed with i2c-tools and is
		+	meant to be included from user-space programs. You obviously want
		+	the second one here.
		+
		+	Now, you have to decide which adapter you want to access. You should
		+	inspect /sys/class/i2c-dev/ or run "i2cdetect -l" to decide this.
		+	Adapter numbers are assigned somewhat dynamically, so you can not
		+	assume much about them. They can even change from one boot to the next.
		+
		+	The example values are taken from PCA9551 8 bit GPIO / LED Driver
		+
		+	Next thing, open the device file, as follows:
		+
		+	#include <fcntl.h>
		+	#include <linux/i2c-dev.h>
		+	#include <stdio.h>
		+	#include <stdlib.h>
		+	#include <sys/stat.h>
		+	#include <sys/types.h>
		+
		+	int main(int argc, char *argv[])
		+	{
		+	int file;
		+	int adapter_nr = 0; /* probably dynamically determined */
		+	char filename[20];
		+
		+	snprintf(filename, 19, "/dev/i2c-%d", adapter_nr);
		+	file = open(filename, O_RDWR);
		+	if (file < 0) {
		+	/* ERROR HANDLING; you can check errno to see what went wrong */
		+	exit(1);
		+	}
		+
		+	When you have opened the device, you must specify with what device
		+	address you want to communicate:
		+
		+	int addr = 0x67; /* The I2C address of PCA9551 */
		+
		+	if (ioctl(file, I2C_SLAVE, addr) < 0) {
		+	/* ERROR HANDLING; you can check errno to see what went wrong */
		+	printf("error: ioctl on file failed\n");
		+	exit(1);
		+	}
		+
		+	Well, you are all set up now. You can now use SMBus commands or plain
		+	I2C to communicate with your device. SMBus commands are preferred if
		+	the device supports them. Both are illustrated below.
		+
		+	/* Device register to access */
		+	__u8 reg;
		+	__s32 res;
		+	__u8 value;
		+	char buf[10];
		+
		+	/* read a byte using SMBus commands */
		+	// INPUT (read pin state)
		+	reg = 0x00;
		+	res = i2c_smbus_read_byte_data(file, reg);
		+	if (res < 0) {
		+	/* ERROR HANDLING: i2c transaction failed */
		+	printf("error: i2c read failed\n");
		+	} else {
		+	/* res contains the read word */
		+	printf("LED status: %x\n",res);
		+	}
		+
		+	/* write a byte using SMBus commands */
		+	// LEDs 4-5 on PWM0, LEDs 6-7 on PWM1
		+	reg = 0x06; // register we want to write to
		+	value = 0xfa;
		+	res = i2c_smbus_write_byte_data(file, reg, value);
		+	if (res < 0) {
		+	/* ERROR HANDLING: i2c transaction failed */
		+	printf("error: i2c write failed\n");
		+	}
		+	}
		+
		+	Let the LEDs blink!

I2C on Alix Pcengine - Revision history

Petaflot at 11:05, 5 November 2011

Ndesir: Created page with " http://www.pcengines.info/forums/?page=post&id=DE352734-3123-41F2-AFA4-0CD1939BFDC7&fid=40251191-FF24-48A8-BB0E-995B04812ADE"