From 2da08bcf2e64e5f77ce8b4098ae27101dceef6cc Mon Sep 17 00:00:00 2001
From: Paul Mackerras <paulus@ozlabs.org>
Date: Fri, 8 Jul 2022 16:37:12 +1000
Subject: [PATCH] decode1: Remove stash buffer

Now that the timing of the busy signal from decode2 doesn't depend on
register numbers or downstream instruction completion, we no longer
need the stash buffer on the output of decode1.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
---
 decode1.vhdl | 24 ++++--------------------
 1 file changed, 4 insertions(+), 20 deletions(-)

diff --git a/decode1.vhdl b/decode1.vhdl
index b807054..5bc023b 100644
--- a/decode1.vhdl
+++ b/decode1.vhdl
@@ -30,7 +30,6 @@ end entity decode1;
 
 architecture behaviour of decode1 is
     signal r, rin : Decode1ToDecode2Type;
-    signal s      : Decode1ToDecode2Type;
     signal f, fin : Decode1ToFetch1Type;
 
     constant illegal_inst : decode_rom_t :=
@@ -46,7 +45,6 @@ architecture behaviour of decode1 is
         (override => '0', override_decode => illegal_inst, override_unit => '0', force_single => '0');
 
     signal ri, ri_in : reg_internal_t;
-    signal si        : reg_internal_t;
 
     type br_predictor_t is record
         br_nia    : std_ulogic_vector(61 downto 0);
@@ -555,26 +553,12 @@ begin
         if rising_edge(clk) then
             if rst = '1' then
                 r <= Decode1ToDecode2Init;
-                s <= Decode1ToDecode2Init;
                 ri <= reg_internal_t_init;
-                si <= reg_internal_t_init;
             elsif flush_in = '1' then
                 r.valid <= '0';
-                s.valid <= '0';
-            elsif s.valid = '1' then
-                if stall_in = '0' then
-                    r <= s;
-                    ri <= si;
-                    s.valid <= '0';
-                end if;
-            else
-                s <= rin;
-                si <= ri_in;
-                s.valid <= rin.valid and r.valid and stall_in;
-                if r.valid = '0' or stall_in = '0' then
-                    r <= rin;
-                    ri <= ri_in;
-                end if;
+            elsif stall_in = '0' then
+                r <= rin;
+                ri <= ri_in;
             end if;
             if rst = '1' then
                 br.br_nia <= (others => '0');
@@ -585,7 +569,7 @@ begin
             end if;
         end if;
     end process;
-    busy_out <= s.valid;
+    busy_out <= stall_in;
 
     decode1_1: process(all)
         variable v : Decode1ToDecode2Type;