Permalink
Fetching contributors…
Cannot retrieve contributors at this time
123 lines (84 sloc) 4.47 KB
.. currentmodule:: pyb

class SPI -- a master-driven serial protocol

SPI is a serial protocol that is driven by a master. At the physical level there are 3 lines: SCK, MOSI, MISO.

See usage model of I2C; SPI is very similar. Main difference is parameters to init the SPI bus:

from pyb import SPI
spi = SPI(1, SPI.MASTER, baudrate=600000, polarity=1, phase=0, crc=0x7)

Only required parameter is mode, SPI.MASTER or SPI.SLAVE. Polarity can be 0 or 1, and is the level the idle clock line sits at. Phase can be 0 or 1 to sample data on the first or second clock edge respectively. Crc can be None for no CRC, or a polynomial specifier.

Additional methods for SPI:

data = spi.send_recv(b'1234')        # send 4 bytes and receive 4 bytes
buf = bytearray(4)
spi.send_recv(b'1234', buf)          # send 4 bytes and receive 4 into buf
spi.send_recv(buf, buf)              # send/recv 4 bytes from/to buf

Constructors

Methods

.. method:: SPI.deinit()

   Turn off the SPI bus.

.. method:: SPI.init(mode, baudrate=328125, \*, prescaler, polarity=1, phase=0, bits=8, firstbit=SPI.MSB, ti=False, crc=None)

   Initialise the SPI bus with the given parameters:

     - ``mode`` must be either ``SPI.MASTER`` or ``SPI.SLAVE``.
     - ``baudrate`` is the SCK clock rate (only sensible for a master).
     - ``prescaler`` is the prescaler to use to derive SCK from the APB bus frequency;
       use of ``prescaler`` overrides ``baudrate``.
     - ``polarity`` can be 0 or 1, and is the level the idle clock line sits at.
     - ``phase`` can be 0 or 1 to sample data on the first or second clock edge
       respectively.
     - ``bits`` can be 8 or 16, and is the number of bits in each transferred word.
     - ``firstbit`` can be ``SPI.MSB`` or ``SPI.LSB``.
     - ``crc`` can be None for no CRC, or a polynomial specifier.

   Note that the SPI clock frequency will not always be the requested baudrate.
   The hardware only supports baudrates that are the APB bus frequency
   (see :meth:`pyb.freq`) divided by a prescaler, which can be 2, 4, 8, 16, 32,
   64, 128 or 256.  SPI(1) is on AHB2, and SPI(2) is on AHB1.  For precise
   control over the SPI clock frequency, specify ``prescaler`` instead of
   ``baudrate``.

   Printing the SPI object will show you the computed baudrate and the chosen
   prescaler.

.. method:: SPI.recv(recv, \*, timeout=5000)

   Receive data on the bus:

     - ``recv`` can be an integer, which is the number of bytes to receive,
       or a mutable buffer, which will be filled with received bytes.
     - ``timeout`` is the timeout in milliseconds to wait for the receive.

   Return value: if ``recv`` is an integer then a new buffer of the bytes received,
   otherwise the same buffer that was passed in to ``recv``.

.. method:: SPI.send(send, \*, timeout=5000)

   Send data on the bus:

     - ``send`` is the data to send (an integer to send, or a buffer object).
     - ``timeout`` is the timeout in milliseconds to wait for the send.

   Return value: ``None``.

.. method:: SPI.send_recv(send, recv=None, \*, timeout=5000)

   Send and receive data on the bus at the same time:

     - ``send`` is the data to send (an integer to send, or a buffer object).
     - ``recv`` is a mutable buffer which will be filled with received bytes.
       It can be the same as ``send``, or omitted.  If omitted, a new buffer will
       be created.
     - ``timeout`` is the timeout in milliseconds to wait for the receive.

   Return value: the buffer with the received bytes.

Constants

.. data:: SPI.MASTER
.. data:: SPI.SLAVE

   for initialising the SPI bus to master or slave mode

.. data:: SPI.LSB
.. data:: SPI.MSB

   set the first bit to be the least or most significant bit