From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Mon, 21 Feb 2022 00:26:14 +0000 (+0000)
Subject: again reduce combinatorial chains, similar to Trap pipeline,
X-Git-Url: https://git.libre-soc.org/?p=soc.git;a=commitdiff_plain;h=4586d3fbe87874110d7ca70eaed368237cab8ebd

again reduce combinatorial chains, similar to Trap pipeline,
introduce dummy passthrough stage in Branch pipeline
---

diff --git a/src/soc/fu/branch/pipeline.py b/src/soc/fu/branch/pipeline.py
index 1cdb3e9a..f7c9456e 100644
--- a/src/soc/fu/branch/pipeline.py
+++ b/src/soc/fu/branch/pipeline.py
@@ -1,6 +1,26 @@
 from nmutil.singlepipe import ControlBase
 from nmutil.pipemodbase import PipeModBaseChain
 from soc.fu.branch.main_stage import BranchMainStage
+from nmutil.pipemodbase import PipeModBase
+from soc.fu.branch.pipe_data import BranchInputData
+from nmigen import Module
+
+# gives a 1-clock delay to stop combinatorial link between in and out
+class DummyBranchStage(PipeModBase):
+    def __init__(self, pspec): super().__init__(pspec, "dummy")
+    def ispec(self): return BranchInputData(self.pspec)
+    def ospec(self): return BranchInputData(self.pspec)
+
+    def elaborate(self, platform):
+        m = Module()
+        m.d.comb += self.o.eq(self.i) # pass-through output
+        return m
+
+class BranchDummyStages(PipeModBaseChain):
+    def get_chain(self):
+        dummy = DummyBranchStage(self.pspec)
+        return [dummy]
+
 
 class BranchStages(PipeModBaseChain):
     def get_chain(self):
@@ -12,11 +32,13 @@ class BranchBasePipe(ControlBase):
     def __init__(self, pspec):
         ControlBase.__init__(self)
         self.pspec = pspec
-        self.pipe1 = BranchStages(pspec)
-        self._eqs = self.connect([self.pipe1])
+        self.pipe1 = BranchDummyStages(pspec)
+        self.pipe2 = BranchStages(pspec)
+        self._eqs = self.connect([self.pipe1, self.pipe2])
 
     def elaborate(self, platform):
         m = ControlBase.elaborate(self, platform)
-        m.submodules.pipe = self.pipe1
+        m.submodules.pipe1 = self.pipe1
+        m.submodules.pipe2 = self.pipe2
         m.d.comb += self._eqs
         return m