AM335x PCF8575 Programming

Other Parts Discussed in Thread: PCF8575

Hello

I have PhyBoard-WEGA-AM335x and I'm testing its connection to PCF8575 I2C I/O expander.

I can use it in userspace with i2cset and i2cget, but I have no idea how to program it on C.

Could somebody give me example of reading and writing I/O values from PCF8575?

I've tried to send with ioctl, but all the time I receive "write error". My code below:

 void pcfWrite(char *byte1, char *byte2){        
        struct i2c_rdwr_ioctl_data packets;
	int retVal = -1;
  	struct i2c_msg messages[2];
	messages[0].addr = 0x20;
 	messages[0].flags = 0;
 	messages[0].len = sizeof(byte1);
	messages[0].buf = byte1;
	messages[1].addr = 0x20;
	messages[1].flags = 0;
	messages[1].len = sizeof(byte2);
	messages[1].buf = byte2;
	packets.msgs = messages;
	packets.nmsgs = 2;
	retVal = ioctl("/dev/i2c-1", I2C_RDWR, &packets);
	if (retVal < 0) {
		printf("Error writing\n");
	}
}

Thanks in advance!

P.S. There are no examples neither on Beaglebone community nor on Raspberry

Best regards,

Pavlo