I may just not understand how to do it correctly, but I can't figure out how to write 4 bytes on i2c. I am trying to port this to WiringPi. I got most of the functions working, but color for RGB LEDs is [register + (index*3), r, g, b]. I think this would work, if I had access to i2c_smbus_access:

void wiringpi_8encoder_set_led_color_rgb(uint8_t fd, uint8_t index, uint8_t r, uint8_t g, uint8_t b) {
  uint8_t c[3] = {r, g, b};
  i2c_smbus_access(fd, I2C_SMBUS_WRITE, (index * 3) + RGB_LED_REG, 3, &c);
}

Here is the working python equivalent (self.i2c is from blinka):

def set_led_color_rgb(self, index, red, green, blue):
   self.i2c.writeto(self.address, bytes([index * 3 + RGB_LED_REG, red, green, blue]))    

Is there a better way to do this? I tried writing 4 bytes, 1 at a time, and it did not work (I think because it's adding termination and stuff.)

Would there be interest in a PR to expose i2c_smbus_access as wiringPiI2CWriteRegBytes (so it matches API a bit better) that lets us set the raw bytes/count?

int wiringPiI2CWriteRegBytes (int fd, uint8_t reg, int size, uint_8_t *data);

Would we also need a corresponding wiringPiI2CReadRegBytes?

int wiringPiI2CReadRegBytes (int fd, uint8_t reg, int size, uint_8_t *data);

// usage
uint_8_t *data[8] = {0};
wiringPiI2CReadRegBytes(fd, SOME_REGISTER, 8, data);

Is this basically what is in #130 ?