From 639e64c38831f8f446573c9ccd93beb70d178c2c Mon Sep 17 00:00:00 2001 From: whitequark Date: Mon, 3 Jun 2019 09:23:11 +0000 Subject: [PATCH] vendor.fpga.lattice_ice40: implement differential output buffers. --- nmigen/vendor/fpga/lattice_ice40.py | 87 +++++++++++++++++++++-------- 1 file changed, 65 insertions(+), 22 deletions(-) diff --git a/nmigen/vendor/fpga/lattice_ice40.py b/nmigen/vendor/fpga/lattice_ice40.py index 3ae605c..bf16425 100644 --- a/nmigen/vendor/fpga/lattice_ice40.py +++ b/nmigen/vendor/fpga/lattice_ice40.py @@ -134,16 +134,29 @@ class LatticeICE40Platform(TemplatedPlatform): else: assert False - def _get_dff(self, clk, d, q): - return Instance("$dff", - p_CLK_POLARITY=0, - p_WIDTH=len(d), - i_CLK=clk, - i_D=d, - o_Q=q) - - def _get_io_buffer(self, pin, port, extras): - m = Module() + def _get_io_buffer(self, m, pin, port, extras, o_invert=None): + def _get_dff(clk, d, q): + m.submodules += Instance("$dff", + p_CLK_POLARITY=0, + p_WIDTH=len(d), + i_CLK=clk, + i_D=d, + o_Q=q) + + def _get_inverter(a, invert): + if invert is None: + return a + else: + y = Signal.like(a, name="{}_x{}".format(a.name, 1 if invert else 0)) + for bit in range(len(a)): + m.submodules += Instance("SB_LUT4", + p_LUT_INIT=0b01 if invert else 0b10, + i_I0=a[bit], + i_I1=Const(0), + i_I2=Const(0), + i_I3=Const(0), + o_O=y[bit]) + return y if "GLOBAL" in extras: is_global_input = bool(extras["GLOBAL"]) @@ -151,14 +164,21 @@ class LatticeICE40Platform(TemplatedPlatform): else: is_global_input = False + if "o" in pin.dir: + if pin.xdr < 2: + pin_o = _get_inverter(pin.o, o_invert) + elif pin.xdr == 2: + pin_o0 = _get_inverter(pin.o0, o_invert) + pin_o1 = _get_inverter(pin.o1, o_invert) + if "i" in pin.dir and pin.xdr == 2: i0_ff = Signal.like(pin.i0, name="{}_ff".format(pin.i0.name)) i1_ff = Signal.like(pin.i1, name="{}_ff".format(pin.i1.name)) - m.submodules += self._get_dff(pin.i_clk, i0_ff, pin.i0) - m.submodules += self._get_dff(pin.i_clk, i1_ff, pin.i1) + _get_dff(pin.i_clk, i0_ff, pin.i0) + _get_dff(pin.i_clk, i1_ff, pin.i1) if "o" in pin.dir and pin.xdr == 2: o1_ff = Signal.like(pin.o1, name="{}_ff".format(pin.o1.name)) - m.submodules += self._get_dff(pin.o_clk, pin.o1, o1_ff) + _get_dff(pin.o_clk, pin_o1, o1_ff) for bit in range(len(port)): io_args = [ @@ -205,11 +225,11 @@ class LatticeICE40Platform(TemplatedPlatform): io_args.append(("o", "D_IN_1", i1_ff)) if "o" in pin.dir: if pin.xdr < 2: - io_args.append(("i", "D_OUT_0", pin.o[bit])) + io_args.append(("i", "D_OUT_0", pin_o[bit])) elif pin.xdr == 2: # Re-register negedge output after it leaves fabric. This increases setup time # to an entire cycle, and doesn't add latency. - io_args.append(("i", "D_OUT_0", pin.o0[bit])) + io_args.append(("i", "D_OUT_0", pin_o0[bit])) io_args.append(("i", "D_OUT_1", o1_ff)) if pin.dir in ("oe", "io"): @@ -220,27 +240,33 @@ class LatticeICE40Platform(TemplatedPlatform): else: m.submodules += Instance("SB_IO", *io_args) - return m - def get_input(self, pin, port, extras): self._check_feature("single-ended input", pin, extras, valid_xdrs=(0, 1, 2), valid_extras=True) - return self._get_io_buffer(pin, port, extras) + m = Module() + self._get_io_buffer(m, pin, port, extras) + return m def get_output(self, pin, port, extras): self._check_feature("single-ended output", pin, extras, valid_xdrs=(0, 1, 2), valid_extras=True) - return self._get_io_buffer(pin, port, extras) + m = Module() + self._get_io_buffer(m, pin, port, extras) + return m def get_tristate(self, pin, port, extras): self._check_feature("single-ended tristate", pin, extras, valid_xdrs=(0, 1, 2), valid_extras=True) - return self._get_io_buffer(pin, port, extras) + m = Module() + self._get_io_buffer(m, pin, port, extras) + return m def get_input_output(self, pin, port, extras): self._check_feature("single-ended input/output", pin, extras, valid_xdrs=(0, 1, 2), valid_extras=True) - return self._get_io_buffer(pin, port, extras) + m = Module() + self._get_io_buffer(m, pin, port, extras) + return m def get_diff_input(self, pin, p_port, n_port, extras): self._check_feature("differential input", pin, extras, @@ -250,7 +276,24 @@ class LatticeICE40Platform(TemplatedPlatform): # between LP/HX and UP series: # * for LP/HX, z=0 is DPxxB (B is non-inverting, A is inverting) # * for UP, z=0 is IOB_xxA (A is non-inverting, B is inverting) - return self._get_io_buffer(pin, p_port, extras) + m = Module() + self._get_io_buffer(m, pin, p_port, extras) + return m + + def get_diff_output(self, pin, p_port, n_port, extras): + self._check_feature("differential output", pin, extras, + valid_xdrs=(0, 1, 2), valid_extras=True) + m = Module() + # Note that the non-inverting output pin is not driven the same way as a regular + # output pin. The inverter introduces a delay, so for a non-inverting output pin, + # an identical delay is introduced by instantiating a LUT. This makes the waveform + # perfectly symmetric in the xdr=0 case. + self._get_io_buffer(m, pin, p_port, extras, o_invert=False) + self._get_io_buffer(m, pin, n_port, extras, o_invert=True) + return m + + # Tristate and bidirectional buffers are not supported on iCE40 because it requires external + # termination, which is incompatible for input and output differential I/Os. class IceStormProgrammerMixin: -- 2.30.2