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coredevice.spi, doc/manual: add spi

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Robert Jördens 2016-03-01 21:29:09 +01:00
parent 2cc1dfaee3
commit 0456169558
2 changed files with 163 additions and 6 deletions
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160
artiq/coredevice/spi.py
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@ -21,9 +21,25 @@ 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 ref_period: clock period of the SPI core.
:param channel: channel number of the SPI bus to control.
:param channel: RTIO channel number of the SPI bus to control.
"""
def __init__(self, dmgr, ref_period, channel):
self.core = dmgr.get("core")
@ -43,12 +59,69 @@ class SPIMaster:
@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.
"""
write_div = round(1/(write_freq*self.ref_period))
read_div = round(1/(read_freq*self.ref_period))
self.set_config_mu(flags, write_div, read_div)
@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)
@ -57,6 +130,43 @@ class SPIMaster:
@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 +
@ -65,24 +175,64 @@ class SPIMaster:
@kernel
def write(self, data):
"""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
RTIO-to-Wishbone bus transaction (three RTIO clock cycles).
"""
rtio_output(now_mu(), self.channel, SPI_DATA_ADDR, data)
delay_mu(3*self.ref_period_mu)
@kernel
def read_async(self):
# every read_async() must be matched by an input_async()
"""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):
# matches the preeeding read_async()
"""Retrieves data written asynchronously.
:meth:`input_async` must match a preeeding :meth:`read_async`.
"""
return rtio_input_data(self.channel)
@kernel
def read_sync(self):
rtio_output(now_mu(), self.channel, SPI_DATA_ADDR | SPI_RT2WB_READ, 0)
return rtio_input_data(self.channel)
"""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):

7
doc/manual/core_drivers_reference.rst
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@ -24,6 +24,13 @@ These drivers are for the core device and the peripherals closely integrated int
.. automodule:: artiq.coredevice.dds
:members:
:mod:`artiq.coredevice.spi` module
----------------------------------
.. automodule:: artiq.coredevice.spi
:members:
:mod:`artiq.coredevice.exceptions` module
-----------------------------------------