From d96e9f57aff0393cfe168f004ebab42c48c7ba46 Mon Sep 17 00:00:00 2001
From: Lucas Bollen <lucas@qbaylogic.com>
Date: Fri, 28 Jun 2024 11:32:28 +0200
Subject: [PATCH] Add `ReqResp` Protocol

A simple protocol for request-response transactions
---
 clash-protocols.cabal    |  1 +
 src/Protocols/ReqResp.hs | 46 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+)
 create mode 100644 src/Protocols/ReqResp.hs

diff --git a/clash-protocols.cabal b/clash-protocols.cabal
index 811b853e..862be025 100644
--- a/clash-protocols.cabal
+++ b/clash-protocols.cabal
@@ -179,6 +179,7 @@ library
     Protocols.Internal.Units.TH
     Protocols.Plugin
     Protocols.Plugin.Internal
+    Protocols.ReqResp
     Protocols.Wishbone
     Protocols.Wishbone.Standard
     Protocols.Wishbone.Standard.Hedgehog
diff --git a/src/Protocols/ReqResp.hs b/src/Protocols/ReqResp.hs
new file mode 100644
index 00000000..fc589a67
--- /dev/null
+++ b/src/Protocols/ReqResp.hs
@@ -0,0 +1,46 @@
+{- |
+Simple protocol for request-response communication.
+The forward channel channel has type @Signal dom (Maybe req)@ and is used to send requests.
+The backward channel has type @Signal dom (Maybe resp)@ and is used to send responses.
+The protocol must obey the following rules:
+* When the forward channel is @Just a@, it must not change until the transaction is completed.
+* The forward channel can not depend on the backward channel.
+* When the forward channel is @Nothing@, the backward channel may be undefined.
+-}
+module Protocols.ReqResp where
+
+import qualified Clash.Prelude as C
+import Data.Kind (Type)
+import Protocols
+import Protocols.Internal.Classes
+import Prelude as P
+
+{- | For simple request-response protocols. The forward channel is used to send requests
+and the backward channel is used to send responses.
+Rules:
+* When the forward channel is @Just a@, it must not change until the transaction
+  is completed.
+* The forward channel can not depend on the backward channel.
+* When the forward channel is @Nothing@, the backward channel may be undefined.
+-}
+data ReqResp (dom :: C.Domain) (req :: Type) (resp :: Type)
+
+instance Protocol (ReqResp dom req resp) where
+  -- \| Forward channel for ReqResp protocol:
+  type Fwd (ReqResp dom req resp) = C.Signal dom (Maybe req)
+
+  -- \| Backward channel for ReqResp protocol:
+  type Bwd (ReqResp dom req resp) = C.Signal dom (Maybe resp)
+
+instance IdleCircuit (ReqResp dom req resp) where
+  idleFwd _ = pure Nothing
+  idleBwd _ = pure Nothing
+
+{- | Force a @Nothing@ on the backward channel and @Nothing@ on the forward
+channel if reset is asserted.
+-}
+forceResetSanity ::
+  forall dom req resp.
+  (C.HiddenReset dom) =>
+  Circuit (ReqResp dom req resp) (ReqResp dom req resp)
+forceResetSanity = forceResetSanityGeneric