soc/cores: add PRBS (Pseudo Random Binary Sequence) Generator/Checker

Imported from LiteICLink. PRBS can be useful for different purposes, so is
better integrated in LiteX.

diff --git a/litex/soc/cores/prbs.py b/litex/soc/cores/prbs.py
new file mode 100644 (file)
index 0000000..365fb32
--- /dev/null
+++ b/litex/soc/cores/prbs.py
@@ -0,0 +1,160 @@
+from operator import xor, add
+from functools import reduce
+
+from migen import *
+from migen.genlib.cdc import MultiReg
+
+
+class PRBSGenerator(Module):
+    def __init__(self, n_out, n_state=23, taps=[17, 22]):
+        self.o = Signal(n_out)
+
+        # # #
+
+        state = Signal(n_state, reset=1)
+        curval = [state[i] for i in range(n_state)]
+        curval += [0]*(n_out - n_state)
+        for i in range(n_out):
+            nv = reduce(xor, [curval[tap] for tap in taps])
+            curval.insert(0, nv)
+            curval.pop()
+
+        self.sync += [
+            state.eq(Cat(*curval[:n_state])),
+            self.o.eq(Cat(*curval))
+        ]
+
+
+class PRBS7Generator(PRBSGenerator):
+    def __init__(self, n_out):
+        PRBSGenerator.__init__(self, n_out, n_state=7, taps=[5, 6])
+
+
+class PRBS15Generator(PRBSGenerator):
+    def __init__(self, n_out):
+        PRBSGenerator.__init__(self, n_out, n_state=15, taps=[13, 14])
+
+
+class PRBS31Generator(PRBSGenerator):
+    def __init__(self, n_out):
+        PRBSGenerator.__init__(self, n_out, n_state=31, taps=[27, 30])
+
+
+class PRBSTX(Module):
+    def __init__(self, width, reverse=False):
+        self.config = Signal(2)
+        self.i = Signal(width)
+        self.o = Signal(width)
+
+        # # #
+
+        config = Signal(2)
+
+        # generators
+        self.specials += MultiReg(self.config, config)
+        prbs7 = PRBS7Generator(width)
+        prbs15 = PRBS15Generator(width)
+        prbs31 = PRBS31Generator(width)
+        self.submodules += prbs7, prbs15, prbs31
+
+        # select
+        prbs_data = Signal(width)
+        self.comb += \
+            If(config == 0b11,
+                prbs_data.eq(prbs31.o)
+            ).Elif(config == 0b10,
+                prbs_data.eq(prbs15.o)
+            ).Else(
+                prbs_data.eq(prbs7.o)
+            )
+
+        # optional bits reversing
+        if reverse:
+            new_prbs_data = Signal(width)
+            self.comb += new_prbs_data.eq(prbs_data[::-1])
+            prbs_data = new_prbs_data
+
+        # prbs / data mux
+        self.comb += \
+            If(config == 0,
+                self.o.eq(self.i)
+            ).Else(
+                self.o.eq(prbs_data)
+            )
+
+
+class PRBSChecker(Module):
+    def __init__(self, n_in, n_state=23, taps=[17, 22]):
+        self.i = Signal(n_in)
+        self.errors = Signal(n_in)
+
+        # # #
+
+        state = Signal(n_state, reset=1)
+        curval = [state[i] for i in range(n_state)]
+        for i in reversed(range(n_in)):
+            correctv = reduce(xor, [curval[tap] for tap in taps])
+            self.sync += self.errors[i].eq(self.i[i] != correctv)
+            curval.insert(0, self.i[i])
+            curval.pop()
+
+        self.sync += state.eq(Cat(*curval[:n_state]))
+
+
+class PRBS7Checker(PRBSChecker):
+    def __init__(self, n_out):
+        PRBSChecker.__init__(self, n_out, n_state=7, taps=[5, 6])
+
+
+class PRBS15Checker(PRBSChecker):
+    def __init__(self, n_out):
+        PRBSChecker.__init__(self, n_out, n_state=15, taps=[13, 14])
+
+
+class PRBS31Checker(PRBSChecker):
+    def __init__(self, n_out):
+        PRBSChecker.__init__(self, n_out, n_state=31, taps=[27, 30])
+
+
+class PRBSRX(Module):
+    def __init__(self, width, reverse=False):
+        self.i = Signal(width)
+        self.config = Signal(2)
+        self.errors = Signal(32)
+
+        # # #
+
+        config = Signal(2)
+
+        # optional bits reversing
+        prbs_data = self.i
+        if reverse:
+            new_prbs_data = Signal(width)
+            self.comb += new_prbs_data.eq(prbs_data[::-1])
+            prbs_data = new_prbs_data
+
+        # checkers
+        self.specials += MultiReg(self.config, config)
+        prbs7 = PRBS7Checker(width)
+        prbs15 = PRBS15Checker(width)
+        prbs31 = PRBS31Checker(width)
+        self.submodules += prbs7, prbs15, prbs31
+        self.comb += [
+            prbs7.i.eq(prbs_data),
+            prbs15.i.eq(prbs_data),
+            prbs31.i.eq(prbs_data)
+        ]
+
+        # errors count
+        self.sync += \
+            If(config == 0,
+                self.errors.eq(0)
+            ).Elif(self.errors != (2**32-1),
+                If(config == 0b01,
+                    self.errors.eq(self.errors + (prbs7.errors != 0))
+                ).Elif(config == 0b10,
+                    self.errors.eq(self.errors + (prbs15.errors != 0))
+                ).Elif(config == 0b11,
+                    self.errors.eq(self.errors + (prbs31.errors != 0))
+                )
+            )