memtest: LFSR

diff --git a/milkymist/memtest/__init__.py b/milkymist/memtest/__init__.py
new file mode 100644 (file)
index 0000000..3062caf
--- /dev/null
+++ b/milkymist/memtest/__init__.py
@@ -0,0 +1,30 @@
+from migen.fhdl.std import *
+from migen.genlib.misc import optree
+from migen.fhdl import verilog
+
+class LFSR(Module):
+       def __init__(self, n_out, n_state=31, taps=[27, 30]):
+               self.ce = Signal()
+               self.o = Signal(n_out)
+
+               ###
+
+               state = Signal(n_state)
+               curval = [state[i] for i in range(n_state)]
+               curval += [0]*(n_out - n_state)
+               for i in range(n_out):
+                       nv = optree("^", [curval[tap] for tap in taps])
+                       curval.insert(0, nv)
+                       curval.pop()
+
+               self.sync += If(self.ce,
+                               state.eq(Cat(*curval[:n_state])),
+                               self.o.eq(Cat(*curval))
+                       )
+
+def _printcode():
+       dut = LFSR(3, 4, [3, 2])
+       print(verilog.convert(dut, ios={dut.ce, dut.o}))
+
+if __name__ == "__main__":
+       _printcode()