From a5ed42ec6860f662f63c201e2c646618461497e6 Mon Sep 17 00:00:00 2001
From: Florent Kermarrec <florent@enjoy-digital.fr>
Date: Sat, 17 Nov 2018 17:29:45 +0100
Subject: [PATCH] soc/interconnect/stream: add Gearbox

---
 litex/soc/interconnect/stream.py | 57 +++++++++++++++++++++++++++++
 test/test_gearbox.py             | 62 +++++++++++++++++++-------------
 2 files changed, 94 insertions(+), 25 deletions(-)

diff --git a/litex/soc/interconnect/stream.py b/litex/soc/interconnect/stream.py
index 5a070ea7e..3676a1f63 100644
--- a/litex/soc/interconnect/stream.py
+++ b/litex/soc/interconnect/stream.py
@@ -1,3 +1,5 @@
+import math
+
 from migen import *
 from migen.genlib.record import *
 from migen.genlib import fifo
@@ -355,6 +357,61 @@ class StrideConverter(Module):
             raise ValueError
 
 
+def lcm(a, b):
+    return (a*b)//math.gcd(a, b)
+
+
+def inc_mod(s, m):
+    return [s.eq(s + 1), If(s == (m -1), s.eq(0))]
+
+
+class Gearbox(Module):
+    def __init__(self, i_dw, o_dw):
+        self.sink = sink = Endpoint([("data", i_dw)])
+        self.source = source = Endpoint([("data", o_dw)])
+
+        # # #
+
+        io_lcm = lcm(i_dw, o_dw)
+
+        # control path
+
+        level     = Signal(max=io_lcm)
+        i_inc    = Signal()
+        i_count  = Signal(max=io_lcm//i_dw)
+        o_inc   = Signal()
+        o_count = Signal(max=io_lcm//o_dw)
+
+        self.comb += [
+            sink.ready.eq(level < (io_lcm - i_dw)),
+            source.valid.eq(level >= o_dw),
+        ]
+        self.comb += [
+            i_inc.eq(sink.valid & sink.ready),
+            o_inc.eq(source.valid & source.ready)
+        ]
+        self.sync += [
+            If(i_inc, *inc_mod(i_count, io_lcm//i_dw)),
+            If(o_inc, *inc_mod(o_count, io_lcm//o_dw)),
+            If(i_inc & ~o_inc, level.eq(level + i_dw)),
+            If(~i_inc & o_inc, level.eq(level - o_dw)),
+            If(i_inc & o_inc, level.eq(level + i_dw - o_dw))
+        ]
+
+        # data path
+
+        shift_register = Signal(io_lcm)
+
+        i_cases = {}
+        for i in range(io_lcm//i_dw):
+            i_cases[i] = shift_register[i_dw*i:i_dw*(i+1)].eq(sink.data)
+        self.sync += If(sink.valid & sink.ready, Case(i_count, i_cases))
+
+        o_cases = {}
+        for i in range(io_lcm//o_dw):
+            o_cases[i] = source.data.eq(shift_register[o_dw*i:o_dw*(i+1)])
+        self.comb += Case(o_count, o_cases)
+
 # TODO: clean up code below
 # XXX
 
diff --git a/test/test_gearbox.py b/test/test_gearbox.py
index 9ec2ad2d6..cf444d0bf 100644
--- a/test/test_gearbox.py
+++ b/test/test_gearbox.py
@@ -2,42 +2,54 @@ import unittest
 import random
 
 from migen import *
-from migen.genlib.cdc import Gearbox
 
-# TODO:
-# connect two gearbox together:
-# first gearbox: iwidth > owidth
-# second gearbox: iwidth < owidth
-# use 2 clock domains
-# compare input data to output data, should be similar
-# various datawidth/clock ratios
+from litex.soc.interconnect.stream import Gearbox
 
 
-def data_generator(dut):
-    for i in range(256):
-        yield dut.i.eq(i)
+def data_generator(dut, gearbox, datas):
+    prng = random.Random(42)
+    for i, data in enumerate(datas):
+        while prng.randrange(4):
+            yield
+        yield gearbox.sink.valid.eq(1)
+        yield gearbox.sink.data.eq(data)
         yield
-    yield
+        while (yield gearbox.sink.ready) == 0:
+            yield
+        yield gearbox.sink.valid.eq(0)
 
-@passive
-def data_checker(dut):
-    while True:
-        #print((yield dut.o))
-        yield
+
+def data_checker(dut, gearbox, datas):
+        prng = random.Random(42)
+        dut.errors = 0
+        for i, reference in enumerate(datas):
+            yield gearbox.source.ready.eq(1)
+            yield
+            while (yield gearbox.source.valid) == 0:
+                yield
+            data =  (yield gearbox.source.data)
+            if data != reference:
+                dut.errors += 1
+            yield gearbox.source.ready.eq(0)
+            while prng.randrange(4):
+                yield
 
 
 class GearboxDUT(Module):
     def __init__(self):
-        self.submodules.gearbox_down = Gearbox(10, "user", 8, "gearbox")
-        self.submodules.gearbox_up = Gearbox(8, "gearbox", 10, "user")
-        self.comb += self.gearbox_up.i.eq(self.gearbox_down.o)
-        self.i, self.o = self.gearbox_down.i, self.gearbox_up.o
+        self.submodules.gearbox0 = Gearbox(20, 32)
+        self.submodules.gearbox1 = Gearbox(32, 20)
+        self.comb += self.gearbox0.source.connect(self.gearbox1.sink)
 
 
 class TestGearbox(unittest.TestCase):
     def test_gearbox(self):
+        prng = random.Random(42)
         dut = GearboxDUT()
-        generators = {"user": [data_generator(dut), data_checker(dut)]}
-        clocks = {"user": 12.5, "gearbox": 10}
-        run_simulation(dut, generators, clocks, vcd_name="sim.vcd")
-        self.assertEqual(0, 0)
+        datas = [prng.randrange(2**20) for i in range(128)]
+        generators = [
+            data_generator(dut, dut.gearbox0, datas),
+            data_checker(dut, dut.gearbox1, datas)
+        ]
+        run_simulation(dut, generators, vcd_name="sim.vcd")
+        self.assertEqual(dut.errors, 0)