artiq/artiq/coredevice/spi.py

from artiq.language.core import (kernel, portable, seconds_to_mu, now_mu,
                                 delay_mu, int, mu_to_seconds)
from artiq.language.units import MHz
from artiq.coredevice.rtio import rtio_output, rtio_input_data


SPI_DATA_ADDR, SPI_XFER_ADDR, SPI_CONFIG_ADDR = range(3)
(
    SPI_OFFLINE,
    SPI_ACTIVE,
    SPI_PENDING,
    SPI_CS_POLARITY,
    SPI_CLK_POLARITY,
    SPI_CLK_PHASE,
    SPI_LSB_FIRST,
    SPI_HALF_DUPLEX,
) = (1 << i for i in range(8))

SPI_RT2WB_READ = 1 << 2


class SPIMaster:
    """Core device Serial Peripheral Interface (SPI) bus master.
    Owns one SPI bus.

    **Transfer Sequence**:

    * If desired, write the ``config`` register (:meth:`set_config`)
      to configure and activate the core.
    * If desired, write the ``xfer`` register (:meth:`set_xfer`)
      to set ``cs_n``, ``write_length``, and ``read_length``.
    * :meth:`write` to the ``data`` register (also for transfers with
      zero bits to be written). Writing starts the transfer.
    * If desired, :meth:`read_sync` (or :meth:`read_async` followed by a
      :meth:`input_async` later) the ``data`` register corresponding to
      the last completed transfer.
    * If desired, :meth:`set_xfer` for the next transfer.
    * If desired, :meth:`write` ``data`` queuing the next
      (possibly chained) transfer.

    :param channel: RTIO channel number of the SPI bus to control.
    """
    def __init__(self, dmgr, channel, core_device="core"):
        self.core = dmgr.get(core_device)
        self.ref_period_mu = seconds_to_mu(self.core.coarse_ref_period,
                                           self.core)
        self.channel = channel
        self.write_period_mu = int(0, 64)
        self.read_period_mu = int(0, 64)
        self.xfer_period_mu = int(0, 64)
        # A full transfer takes write_period_mu + xfer_period_mu.
        # Chained transfers can happen every xfer_period_mu.
        # The second transfer of a chain can be written 2*ref_period_mu
        # after the first. Read data is available every xfer_period_mu starting
        # a bit after xfer_period_mu (depending on clk_phase).
        # To chain transfers together, new data must be written before
        # pending transfer's read data becomes available.

    @portable
    def frequency_to_div(self, f):
        return int(1/(f*mu_to_seconds(self.ref_period_mu))) + 1

    @kernel
    def set_config(self, flags=0, write_freq=20*MHz, read_freq=20*MHz):
        """Set the configuration register.

        * If ``config.cs_polarity`` == 0 (```cs`` active low, the default),
          "``cs_n`` all deasserted" means "all ``cs_n`` bits high".
        * ``cs_n`` is not mandatory in the pads supplied to the gateware core.
          Framing and chip selection can also be handled independently
          through other means, e.g. ``TTLOut``.
        * If there is a ``miso`` wire in the pads supplied in the gateware,
          input and output may be two signals ("4-wire SPI"),
          otherwise ``mosi`` must be used for both output and input
          ("3-wire SPI") and ``config.half_duplex`` must to be set
          when reading data is desired or when the slave drives the
          ``mosi`` signal at any point.
        * The first bit output on ``mosi`` is always the MSB/LSB (depending
          on ``config.lsb_first``) of the ``data`` register, independent of
          ``xfer.write_length``. The last bit input from ``miso`` always ends
          up in the LSB/MSB (respectively) of the ``data`` register,
          independent of ``xfer.read_length``.
        * Writes to the ``config`` register take effect immediately.

        **Configuration flags**:

        * :const:`SPI_OFFLINE`: all pins high-z (reset=1)
        * :const:`SPI_ACTIVE`: transfer in progress (read-only)
        * :const:`SPI_PENDING`: transfer pending in intermediate buffer
          (read-only)
        * :const:`SPI_CS_POLARITY`: active level of ``cs_n`` (reset=0)
        * :const:`SPI_CLK_POLARITY`: idle level of ``clk`` (reset=0)
        * :const:`SPI_CLK_PHASE`: first edge after ``cs`` assertion to sample
          data on (reset=0). In Motorola/Freescale SPI language
          (:const:`SPI_CLK_POLARITY`, :const:`SPI_CLK_PHASE`) == (CPOL, CPHA):

          - (0, 0): idle low, output on falling, input on rising
          - (0, 1): idle low, output on rising, input on falling
          - (1, 0): idle high, output on rising, input on falling
          - (1, 1): idle high, output on falling, input on rising
        * :const:`SPI_LSB_FIRST`: LSB is the first bit on the wire (reset=0)
        * :const:`SPI_HALF_DUPLEX`: 3-wire SPI, in/out on ``mosi`` (reset=0)

        This method advances the timeline by the duration of the
        RTIO-to-Wishbone bus transaction (three RTIO clock cycles).

        :param flags: A bit map of `SPI_*` flags.
        :param write_freq: Desired SPI clock frequency during write bits.
        :param read_freq: Desired SPI clock frequency during read bits.
        """
        self.set_config_mu(flags, self.frequency_to_div(write_freq),
                           self.frequency_to_div(read_freq))

    @kernel
    def set_config_mu(self, flags=0, write_div=6, read_div=6):
        """Set the ``config`` register (in SPI bus machine units).

        .. seealso:: :meth:`set_config`

        :param write_div: Counter load value to divide the RTIO
          clock by to generate the SPI write clk. (minimum=2, reset=2)
          ``f_rtio_clk/f_spi_write == write_div``. If ``write_div`` is odd,
          the setup phase of the SPI clock is biased to longer lengths
          by one RTIO clock cycle.
        :param read_div: Ditto for the read clock.
        """
        rtio_output(now_mu(), self.channel, SPI_CONFIG_ADDR, flags |
                    ((write_div - 2) << 16) | ((read_div - 2) << 24))
        self.write_period_mu = int(write_div*self.ref_period_mu)
        self.read_period_mu = int(read_div*self.ref_period_mu)
        delay_mu(3*self.ref_period_mu)

    @kernel
    def set_xfer(self, chip_select=0, write_length=0, read_length=0):
        """Set the ``xfer`` register.

        * Every transfer consists of a write of ``write_length`` bits
          immediately followed by a read of ``read_length`` bits.
        * ``cs_n`` is asserted at the beginning and deasserted at the end
          of the transfer if there is no other transfer pending.
        * ``cs_n`` handling is agnostic to whether it is one-hot or decoded
          somewhere downstream. If it is decoded, "``cs_n`` all deasserted"
          should be handled accordingly (no slave selected).
          If it is one-hot, asserting multiple slaves should only be attempted
          if ``miso`` is either not connected between slaves, or open
          collector, or correctly multiplexed externally.
        * For 4-wire SPI only the sum of ``read_length`` and ``write_length``
          matters. The behavior is the same (except for clock speeds) no matter
          how the total transfer length is divided between the two. For
          3-wire SPI, the direction of ``mosi`` is switched from output to
          input after ``write_length`` bits.
        * Data output on ``mosi`` in 4-wire SPI during the read cycles is what
          is found in the data register at the time.
          Data in the ``data`` register outside the least/most (depending
          on ``config.lsb_first``) significant ``read_length`` bits is what is
          seen on ``miso`` (or ``mosi`` if ``config.half_duplex``)
          during the write cycles.
        * Writes to ``xfer`` are synchronized to the start of the next
          (possibly chained) transfer.

        This method advances the timeline by the duration of the
        RTIO-to-Wishbone bus transaction (three RTIO clock cycles).

        :param chip_select: Bit mask of chip selects to assert. Or number of
            the chip select to assert if ``cs`` is decoded downstream.
            (reset=0)
        :param write_length: Number of bits to write during the next transfer.
            (reset=0)
        :param read_length: Number of bits to read during the next transfer.
            (reset=0)
        """
        rtio_output(now_mu(), self.channel, SPI_XFER_ADDR,
                    chip_select | (write_length << 16) | (read_length << 24))
        self.xfer_period_mu = int(write_length*self.write_period_mu +
                                  read_length*self.read_period_mu)
        delay_mu(3*self.ref_period_mu)

    @kernel
    def write(self, data=0):
        """Write data to data register.

        * The ``data`` register and the shift register are 32 bits wide.
          If there are no writes to the register, ``miso`` data reappears on
          ``mosi`` after 32 cycles.
        * A wishbone data register write is acknowledged when the
          transfer has been written to the intermediate buffer.
          It will be started when there are no other transactions being
          executed, either beginning a new SPI transfer of chained
          to an in-flight transfer.
        * Writes take three ``ref_period`` cycles unless another
          chained transfer is pending and the transfer being
          executed is not complete.
        * The SPI ``data`` register is double-buffered: Once a transfer has
          started, new write data can be written, queuing a new transfer.
          Transfers submitted this way are chained and executed without
          deasserting ``cs`` in between. Once a transfer completes,
          the previous transfer's read data is available in the
          ``data`` register.

        This method advances the timeline by the duration of the SPI transfer.
        If a transfer is to be chained, the timeline needs to be rewound.
        """
        rtio_output(now_mu(), self.channel, SPI_DATA_ADDR, data)
        delay_mu(self.xfer_period_mu + self.write_period_mu)

    @kernel
    def read_async(self):
        """Trigger an asynchronous read from the ``data`` register.

        Reads always finish in two cycles.

        Every data register read triggered by a :meth:`read_async`
        must be matched by a :meth:`input_async` to retrieve the data.

        This method advances the timeline by the duration of the
        RTIO-to-Wishbone bus transaction (three RTIO clock cycles).
        """
        rtio_output(now_mu(), self.channel, SPI_DATA_ADDR | SPI_RT2WB_READ, 0)
        delay_mu(3*self.ref_period_mu)

    @kernel
    def input_async(self):
        """Retrieves data read asynchronously from the ``data`` register.

        :meth:`input_async` must match a preeeding :meth:`read_async`.
        """
        return rtio_input_data(self.channel)

    @kernel
    def read_sync(self):
        """Read the ``data`` register synchronously.

        This is a shortcut for :meth:`read_async` followed by
        :meth:`input_async`.
        """
        self.read_async()
        return self.input_async()

    @kernel
    def _get_xfer_sync(self):
        rtio_output(now_mu(), self.channel, SPI_XFER_ADDR | SPI_RT2WB_READ, 0)
        return rtio_input_data(self.channel)

    @kernel
    def _get_config_sync(self):
        rtio_output(now_mu(), self.channel, SPI_CONFIG_ADDR | SPI_RT2WB_READ,
                    0)
        return rtio_input_data(self.channel)