I2C Usage difference in Arduino and WiringPi

Question

I'm using a device through I2C interface and I'm having some issues when the I2C bus fails, I don't know if it fails because an interferance in the cable or just timing issues in the Raspberry over high loads.

The thing is that checking the way this device is used in Arduino and Raspberry there is a difference.

In arduino you use it like this:

Wire.beginTransmission(0x27);
Wire.write(0x80);
Wire.write(75);
Wire.endTransmission();

And in RPi you first set the channel into a pointer and then write to it, but never "endTransmission" or "beginTransmission" when you need to send the message.

I just init the i2c channel at the start:

dimmer = wiringPiI2CSetup(0x27);

And then use this to set the values.

wiringPiI2CWrite (dimmer, pin) ;
wiringPiI2CWrite (dimmer, value) ;

The problem is that once in a while it stops working, maybe a message got lost in the middle and now those 2 writes never are together waiting for the next byte. So, is there a difference between the Arduino version and the wiringPi version for this? is there a way to set the begin and end of a transmission?

The device in question is the Kryda AC Dimmer: https://www.tindie.com/products/bugrovs2012/i2c-4ch-ac-led-dimmer-module/

Answer 1

You should use wiringPiI2CWriteReg8 instead of the raw wiringPiI2CWrite:

dimmer = wiringPiI2CSetup(0x27);
wiringPiI2CWriteReg8(dimmer, pin, value);

This keeps everything together in one neat interface. TBH I am not sure how it differs internally, but it certainly gives you a cleaner interface.

Answer 2

The Arduino and Raspberry Pi commands are substantially different.

The Arduino command is sending:

start condition
data 0x80 to address 0x27
data 75 to address 0x27
end condition

The RPi commands are sending.

start condition
data 0x80 to address 0x27
end condition
start condition
data 75 to address 0x27
end condition

Frankly I'm surprised the device accepts the Raspberry Pi data as a valid command.

To do the same as the Arduino you would need code such as the following:

char data[]={0x80, 75};

dimmer = wiringPiI2CSetup(0x27);

write(dimmer, data, 2);