decode1: Implement obsolete dst, dstst, dss instructions as no-ops

[microwatt.git] / cr_hazard.vhdl

diff --git a/cr_hazard.vhdl b/cr_hazard.vhdl
index 2a434ac6b07f4bf069b6c878a5582b0f270b8ad0..a6203a848d62efca7da039f4a9319ba3e5f3ae89 100644 (file)
--- a/cr_hazard.vhdl
+++ b/cr_hazard.vhdl
@@ -4,24 +4,32 @@ use ieee.numeric_std.all;
 
 entity cr_hazard is
     generic (
-        PIPELINE_DEPTH : natural := 2
+        PIPELINE_DEPTH : natural := 1
         );
     port(
-        clk         : in std_logic;
+        clk         : in std_ulogic;
+        busy_in     : in std_ulogic;
+        deferred    : in std_ulogic;
+        complete_in : in std_ulogic;
+        flush_in    : in std_ulogic;
+        issuing     : in std_ulogic;
 
         cr_read_in  : in std_ulogic;
         cr_write_in : in std_ulogic;
+        bypassable  : in std_ulogic;
 
-        stall_out   : out std_ulogic
+        stall_out   : out std_ulogic;
+        use_bypass  : out std_ulogic
         );
 end entity cr_hazard;
 architecture behaviour of cr_hazard is
     type pipeline_entry_type is record
-        valid : std_ulogic;
+        valid  : std_ulogic;
+        bypass : std_ulogic;
     end record;
-    constant pipeline_entry_init : pipeline_entry_type := (valid => '0');
+    constant pipeline_entry_init : pipeline_entry_type := (valid => '0', bypass => '0');
 
-    type pipeline_t is array(0 to PIPELINE_DEPTH-1) of pipeline_entry_type;
+    type pipeline_t is array(0 to PIPELINE_DEPTH) of pipeline_entry_type;
     constant pipeline_t_init : pipeline_t := (others => pipeline_entry_init);
 
     signal r, rin : pipeline_t := pipeline_t_init;
@@ -38,22 +46,37 @@ begin
     begin
         v := r;
 
+        -- XXX assumes PIPELINE_DEPTH = 1
+        if complete_in = '1' then
+            v(1).valid := '0';
+        end if;
+
+        use_bypass <= '0';
         stall_out <= '0';
-        loop_0: for i in 0 to PIPELINE_DEPTH-1 loop
-            if (r(i).valid = cr_read_in) then
-                stall_out <= '1';
-            end if;
-        end loop;
-
-        v(0).valid := cr_write_in;
-        loop_1: for i in 0 to PIPELINE_DEPTH-2 loop
-            -- propagate to next slot
-            v(i+1) := r(i);
-        end loop;
-
-        -- asynchronous output
-        if cr_read_in = '0' then
-            stall_out <= '0';
+        if cr_read_in = '1' then
+            loop_0: for i in 0 to PIPELINE_DEPTH loop
+                if v(i).valid = '1' then
+                    if r(i).bypass = '1' then
+                        use_bypass <= '1';
+                    else
+                        stall_out <= '1';
+                    end if;
+                end if;
+            end loop;
+        end if;
+
+        -- XXX assumes PIPELINE_DEPTH = 1
+        if busy_in = '0' then
+            v(1) := r(0);
+            v(0).valid := '0';
+        end if;
+        if deferred = '0' and issuing = '1' then
+            v(0).valid := cr_write_in;
+            v(0).bypass := bypassable;
+        end if;
+        if flush_in = '1' then
+            v(0).valid := '0';
+            v(1).valid := '0';
         end if;
 
         -- update registers