gateware.spi: design sketch

artiq/gateware/rtio/phy/spi.py

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+from migen import *
+
+from artiq.gateware.spi import SPIMaster as SPIMasterWB
+from artiq.gateware.rtio.phy.wishbone import RT2WB
+
+
+class SPIMaster(Module):
+    def __init__(self, pads, onehot=False, **kwargs):
+        self.submodules._ll = ClockDomainsRenamer("rio")(
+            SPIMasterWB(pads, **kwargs))
+        self.submodules._rt2wb = RT2WB(2, self._ll.bus)
+        self.rtlink = self._rt2wb.rtlink
+        self.probes = []

artiq/gateware/spi.py

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+from migen import *
+from migen.genlib.fsm import *
+from migen.genlib.misc import WaitTimer
+from misoc.interconnect import wishbone
+
+
+class SPIMaster(Module):
+    """SPI Master.
+
+    Notes:
+        * If there is a miso wire in pads, the input and output are done with
+          two signals (a.k.a. 4-wire SPI), else mosi is used for both output
+          and input (a.k.a. 3-wire SPI).
+        * Every transfer consists of a 0-32 bit write followed by a 0-32
+          bit read.
+        * cs_n is always asserted at the beginning and deasserted
+          at the end of the tranfer.
+        * 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.
+        * If config.cs_polarity == 0 (cs active low, the default),
+          "cs_n all deasserted" means "all cs_n bits high".
+        * The first bit output on mosi is always the MSB/LSB (depending on
+          config.lsb_first) of the data register, independent of
+          xfer.write_len. The last bit input from miso always ends up in
+          the LSB/MSB (respectively) of the data register, independent of
+          read_len.
+        * For 4-wire SPI only the sum of read_len and write_len matters. The
+          behavior is the same no matter how the transfer length is divided
+          between the two. For 3-wire SPI, the direction of mosi/miso is
+          switched from output to input after write_len cycles, at the
+          "output" clk edge corresponding to bit write_len + 1 of the transfer.
+        * Data output on mosi in 4-wire SPI during the read cycles is
+          undefined. Data in the data register outside the
+          least/most (depending on config.lsb_first) significant read_len
+          bits is undefined.
+        * The transfer is complete when the wishbone transaction is ack-ed.
+        * Input data from the last transaction can be read from the data
+          register at any time.
+
+    Transaction Sequence:
+        * if desired, write the xfer register to change lengths and cs_n.
+        * write the data register (also for zero-length writes),
+          writing triggers the transfer and the transfer is complete when the
+          write is complete.
+        * if desired, read the data register
+
+    Register address and bit map:
+
+    config (address 0):
+        1 offline: all pins high-z (reset=1)
+        1 cs_polarity: active level of chip select (reset=0)
+        1 clk_polarity: idle level for clk (reset=0)
+        1 clk_phase: first edge after cs assertion to sample data on (reset=0)
+            (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
+        1 lsb_first: LSB is the first bit on the wire (reset=0)
+        11 undefined
+        16 speed: divider from this module's clock to the SPI clk
+            (minimum=2, reset=4)
+            clk pulses are asymmetric if speed is odd, favoring longer setup
+            over hold times
+
+    xfer (address 1):
+        16 cs: active high bit mask of chip selects to assert
+        6 write_len: 0-32 bits
+        2 undefined
+        6 read_len: 0-32 bits
+        2 undefined
+
+    data (address 2):
+        32 write/read data
+    """
+    def __init__(self, pads, bus=None):
+        if bus is None:
+            bus = wishbone.Interface(data_width=32)
+        self.bus = bus
+
+        ###
+
+
+def _test_gen(bus):
+    yield from bus.write(0, 0 | (5 << 16))
+    yield
+    yield from bus.write(1, 1 | (24 << 16) | (16 << 24))
+    yield
+    yield from bus.write(2, 0x12345678)
+    yield
+    r = (yield from bus.read(2))
+    print(r)
+    yield
+
+
+class _TestPads:
+    def __init__(self):
+        self.cs_n = Signal(3)
+        self.clk = Signal()
+        self.mosi = Signal()
+        self.miso = Signal()
+
+
+if __name__ == "__main__":
+    pads = _TestPads()
+    dut = SPIMaster(pads)
+    run_simulation(dut, _test_gen(dut.bus), vcd_name="spi_master.vcd")