spi.py 文件源码

def xfer(self, txbuff=None):
        length = len(txbuff)
        if PYTHON_MAJOR >= 3:
            _txbuff = bytes(txbuff)
            _txptr = ctypes.create_string_buffer(_txbuff)
        else:
            _txbuff = str(bytearray(txbuff))
            _txptr = ctypes.create_string_buffer(_txbuff)
        _rxptr = ctypes.create_string_buffer(length)

        data = struct.pack("QQLLHBBL",  #64 64 32 32 16 8 8 32 b = 32B
                    ctypes.addressof(_txptr),
                    ctypes.addressof(_rxptr),
                    length,
                    self.speed,
                    0, #delay
                    self.bits,
                    0, # cs_change,
                    0  # pad
                    )

        fcntl.ioctl(self.fd, SPI_IOC_MESSAGE(len(data)), data)
        _rxbuff = ctypes.string_at(_rxptr, length)
        return bytearray(_rxbuff)