still workikng on Bus types

bs/BusTypes.bs

@@ -1,4 +1,10 @@
-package BusTypes(BusVal, TransactionSize) where
+package BusTypes(
+    BusVal(..),
+    BusError(..),
+    TransactionSize(..),
+    ReadRequest(..),
+    WriteRequest(..)
+    ) where
 
 import Types
 
@@ -29,5 +35,34 @@ data ReadRequest = ReadRequest Addr TransactionSize
 data WriteRequest = WriteRequest Addr BusVal
     deriving (Bits, Eq, FShow)
 
+type ReadResponse = Either BusError BusVal
+type WriteResponse = Either BusError ()
+
+data BusRequest
+  = BusReadRequest      ReadRequest
+  | WriteReadRequest    WriteRequest
+  deriving (Bits, Eq, FShow)
+
+data BusResponse
+  = BusReadResponse     ReadResponse
+  | BusWriteResponse    WriteResponse
+  deriving (Bits, Eq, FShow)
+
+interface BusMaster =
+  -- The Bus arbiter will call the Bus Client's request method
+  -- if and only if it's the Bus Client's turn to make a request, and the Bus Client
+  -- has a request to make.
+  -- It is up to the BusMaster to guard it's request method such that calling
+  -- it's request method is only valid when the BusMaster has a request to make.
+  -- This has implications about for the implementor of BusMaster, namely, that it
+  -- should hold its request until it's request method gets called.
+  request  :: BusRequest
+  -- From the client's perspective, the response should not be called until
+  -- the client is ready to accept the response. In other words, response
+  -- should be guarded by the client.
+  response :: BusResponse -> Action
+
+type Token = UInt 5
+
 a :: UInt 5
 a = 3