Merge pull request #1021 from antmicro/ddr_sim

litex: Enable simulation of DDR IO by adding oddr/iddr/ddrtristate simulation models.

litex/build/io.py

@@ -147,6 +147,16 @@ class DDROutput(Special):
 
 # DDR Tristate -------------------------------------------------------------------------------------
 
+class InferedDDRTristate(Module):
+    def __init__(self, i1, i2, o1, o2, oe1, oe2, io, clk):
+        _o  = Signal()
+        _oe = Signal()
+        _i  = Signal()
+        self.specials += DDROutput(i1, i2, _o, clk)
+        self.specials += DDROutput(oe1, oe2, _oe, clk)
+        self.specials += DDRInput(_i, o1, o2, clk)
+        self.specials += Tristate(io, _o, _oe, _i)
+
 class DDRTristate(Special):
     def __init__(self, i1, i2, o1, o2, oe1, oe2, io, clk=ClockSignal()):
         Special.__init__(self)
@@ -171,7 +181,7 @@ class DDRTristate(Special):
 
     @staticmethod
     def lower(dr):
-        raise NotImplementedError("Attempted to use a DDR tristate, but platform does not support them")
+        return InferedDDRTristate(dr.i1, dr.i2, dr.o1, dr.o2, dr.oe1, dr.oe2, dr.io, dr.clk)
 
 # Clock Reset Generator ----------------------------------------------------------------------------
 

litex/build/sim/common.py

@@ -1 +1,35 @@
-sim_special_overrides = {}
+from migen import *
+from migen.fhdl.specials import Special
+
+from litex.build.io import *
+
+class InferedDDROutputSim(Module):
+    def __init__(self, o, i1, i2, clk):
+        self.specials += Instance("DDR_OUTPUT",
+                i_i1 = i1,
+                i_i2 = i2,
+                o_o = o,
+                i_clk = clk)
+
+class InferedDDRInputSim(Module):
+    def __init__(self, i, o1, o2, clk):
+        self.specials += Instance("DDR_INPUT",
+                o_o1 = o1,
+                o_o2 = o2,
+                i_i = i,
+                i_clk = clk)
+
+class DDROutputSim:
+    @staticmethod
+    def lower(dr):
+        return InferedDDROutputSim(dr.o, dr.i1, dr.i2, dr.clk)
+
+class DDRInputSim:
+    @staticmethod
+    def lower(dr):
+        return InferedDDRInputSim(dr.i, dr.o1, dr.o2, dr.clk)
+
+sim_special_overrides = {
+    DDROutput: DDROutputSim,
+    DDRInput:  DDRInputSim,
+}

litex/build/sim/verilog/iddr_verilog.v

@@ -0,0 +1,24 @@
+module DDR_INPUT(
+ output reg o1,
+ output reg o2,
+ input i,
+ input clk);
+
+reg _o1, _o2;
+
+always @ (posedge clk)
+  begin
+   o1 = _o1;
+   o2 = _o2;
+  end
+
+always @ (posedge clk)
+    begin
+        _o1 = i;
+    end
+
+always @ (negedge clk)
+    begin
+        _o2 = i;
+    end
+endmodule

litex/build/sim/verilog/oddr_verilog.v

@@ -0,0 +1,19 @@
+module DDR_OUTPUT(
+    input i1,
+    input i2,
+    output o,
+    input clk);
+
+wire _o;
+reg _i1, _i2;
+
+assign o = _o;
+assign _o = (clk) ? _i1 : _i2;
+
+always @ (posedge clk)
+    begin
+        _i1 = i1;
+        _i2 = i2;
+    end
+
+endmodule