FSM - Remove extra step WAIT_INBOX

[adumont]

Limitation in Logisim FSM, doesnt allow to stay in same state (wait here).

Review when implementing with Fizzim / Verilog.

In DECODE state, When ( Instr = INBOX AND empty = 1 ), FSM should stay in DECODE (until empty = 0).

For now I have added the extra step WAIT_INBOX to transition back back to DECODE, to reevaluate again.

Doesn't seem very eficient.

[adumont]

Can be achieved by:

diff --git a/verilog/ControlUnit.v b/verilog/ControlUnit.v
index a182a12..38c0678 100644
--- a/verilog/ControlUnit.v
+++ b/verilog/ControlUnit.v
@@ -104,9 +104,9 @@ module ControlUnit (
                         endcase
         S_COPYFROM    : nextstate = S_Inc_PC;
         S_DECODE      : case (opcode)
-                          o_INBOX  : if( inEmpty ) nextstate = S_WAIT_INBOX;
+                          o_INBOX  : if( inEmpty ) nextstate = S_DECODE;
                                      else          nextstate = S_INBOX;
-                          o_OUTBOX : if( outFull ) nextstate = S_WAIT_OUTBOX;
+                          o_OUTBOX : if( outFull ) nextstate = S_DECODE;
                                      else          nextstate = S_OUTBOX;
                           o_HALT   : nextstate = S_HALT;
                           default  : nextstate = S_INCPC2;

(passes all tests OK).

ALthough now I'm not really sure it's usefull. Sure it's less states, but it's easier to keep it for consistency with the Logisim FSM design...

[adumont]

Implemented in f941c8b