Initialize Pixy and enable Pixy block reporting.
        This is a FirmataPlusRB feature.

        :param cb: callback function to report Pixy blocks

        :param cb_type: Constants.CB_TYPE_DIRECT = direct call or
                        Constants.CB_TYPE_ASYNCIO = asyncio coroutine

        :param max_blocks: Maximum number of Pixy blocks to report when many signatures are found.

        :returns: No return value.

async def pixy_init(self, max_blocks=5, cb=None, cb_type=None):
        """
        Initialize Pixy and enable Pixy block reporting.
        This is a FirmataPlusRB feature.

        :param cb: callback function to report Pixy blocks

        :param cb_type: Constants.CB_TYPE_DIRECT = direct call or
                        Constants.CB_TYPE_ASYNCIO = asyncio coroutine

        :param max_blocks: Maximum number of Pixy blocks to report when many signatures are found.

        :returns: No return value.
        """
        if cb:
            self.digital_pins[PrivateConstants.PIN_PIXY_MOSI].cb = cb  # Pixy uses SPI.  Pin 11 is MOSI.
        if cb_type:
            self.digital_pins[PrivateConstants.PIN_PIXY_MOSI].cb_type = cb_type
        data = [PrivateConstants.PIXY_INIT, max_blocks & 0x7f]
        await self._send_sysex(PrivateConstants.PIXY_CONFIG, data)