code: func (d *GrovePiDriver) WriteAnalog(pin byte, val byte) error {
  	buf := []byte{CommandWriteAnalog, pin, val, 0}
  	_, err := d.connection.Write(buf)
  
  	time.Sleep(2 * time.Millisecond)
  
  	data := make([]byte, 1)
  	_, err = d.connection.Read(data)
  
  	return err
  }
docs: // WriteAnalog writes PWM aka analog to the GrovePi. Not yet working.