From dea46749220fb78154b9cb3355b87275b4339707 Mon Sep 17 00:00:00 2001
From: Lars-Peter Clausen <lars@metafoo.de>
Date: Tue, 12 Mar 2013 22:27:19 +0100
Subject: [PATCH] Allow SimActors to produce/consume a constant stream of
 tokens

Currently a SimActor requires one clock period to recover from consuming or
producing a token. ack/stb are deasserted in the cycle where the token is
consumed/produced and only re-asserted in the next cycle. This patch updates the
code to keep the control signals asserted if the actor is able to produce or
consume a token in the next cycle.

The patch also sets 'initialize' attribute on the simulation method, this will
make sure that the control and data signals will be ready right on the first
clock cycle.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
---
 migen/actorlib/sim.py | 43 +++++++++++++++++++++++++------------------
 1 file changed, 25 insertions(+), 18 deletions(-)

diff --git a/migen/actorlib/sim.py b/migen/actorlib/sim.py
index de11f1c9..18a7bfc9 100644
--- a/migen/actorlib/sim.py
+++ b/migen/actorlib/sim.py
@@ -22,27 +22,31 @@ class TokenExchanger(PureSimulable):
 		for token in self.active:
 			ep = self.actor.endpoints[token.endpoint]
 			if isinstance(ep, Sink):
-				if s.rd(ep.ack):
-					if s.rd(ep.stb):
-						token.value = s.multiread(ep.token)
-						completed.add(token)
-						s.wr(ep.ack, 0)
-				else:
-					s.wr(ep.ack, 1)
+				if s.rd(ep.ack) and s.rd(ep.stb):
+					token.value = s.multiread(ep.token)
+					completed.add(token)
+					s.wr(ep.ack, 0)
 			elif isinstance(ep, Source):
-				if s.rd(ep.stb):
-					if s.rd(ep.ack):
-						completed.add(token)
-						s.wr(ep.stb, 0)
-				else:
-					s.wr(ep.stb, 1)
-					s.multiwrite(ep.token, token.value)
+				if s.rd(ep.ack) and s.rd(ep.stb):
+					completed.add(token)
+					s.wr(ep.stb, 0)
 			else:
 				raise TypeError
 		self.active -= completed
 		if not self.active:
 			self.busy = True
-	
+
+	def _update_control_signals(self, s):
+		for token in self.active:
+			ep = self.actor.endpoints[token.endpoint]
+			if isinstance(ep, Sink):
+				s.wr(ep.ack, 1)
+			elif isinstance(ep, Source):
+				s.multiwrite(ep.token, token.value)
+				s.wr(ep.stb, 1)
+			else:
+				raise TypeError
+
 	def _next_transactions(self):
 		try:
 			transactions = next(self.generator)
@@ -62,13 +66,16 @@ class TokenExchanger(PureSimulable):
 			raise TypeError
 		if self.active and all(transaction.idle_wait for transaction in self.active):
 			self.busy = False
-	
+
 	def do_simulation(self, s):
 		if not self.done:
-			if not self.active:
-				self._next_transactions()
 			if self.active:
 				self._process_transactions(s)
+			if not self.active:
+				self._next_transactions()
+				self._update_control_signals(s)
+
+	do_simulation.initialize = True
 
 class SimActor(Actor):
 	def __init__(self, generator, *endpoint_descriptions, **misc):
-- 
2.30.2