core.vhd missing in CAUSE always updated -- except if STATUS.EXL=1

cMIPS/vhdl/core.vhd

@@ -156,7 +156,7 @@ architecture rtl of core is
   signal update, not_stalled: std_logic;
   signal update_reg : reg5;
   signal status_update,epc_update,compare_update: std_logic;
-  signal cause_update, disable_count, compare_set, compare_clr: std_logic;
+  signal disable_count, compare_set, compare_clr: std_logic;
   signal STATUSinp,STATUS, CAUSEinp,CAUSE, EPCinp,EPC : reg32;
   signal COUNT, COMPARE : reg32;
   signal count_eq_compare,count_update,count_enable : std_logic;
@@ -2327,31 +2327,31 @@ begin
     variable newCAUSE : reg32;
   begin
 
-    if STATUS(STATUS_EXL) = '0' then
-      newCAUSE(CAUSE_BD)   := is_delayslot;     -- instr is in delay slot
+    if STATUS(STATUS_EXL) = '0' then            -- no exception, update CAUSE 
+      newCAUSE(CAUSE_BD)   := is_delayslot;
+      newCAUSE(CAUSE_TI)     := count_eq_compare;
+      newCAUSE(CAUSE_CE1)    := '0';
+      newCAUSE(CAUSE_CE0)    := '0';
+      newCAUSE(CAUSE_DC)     := CAUSE(CAUSE_DC);
+      newCAUSE(CAUSE_PCI)    := '0';
+      newCAUSE(25 downto 24) := b"00";
+      newCAUSE(CAUSE_IV)     := CAUSE(CAUSE_IV);
+      newCAUSE(CAUSE_WP)     := '0';
+      newCAUSE(21 downto 16) := b"000000";      
+      newCAUSE(CAUSE_IP7)    := MM_int_req(7);
+      newCAUSE(CAUSE_IP6)    := MM_int_req(6);
+      newCAUSE(CAUSE_IP5)    := MM_int_req(5);
+      newCAUSE(CAUSE_IP4)    := MM_int_req(4);
+      newCAUSE(CAUSE_IP3)    := MM_int_req(3);
+      newCAUSE(CAUSE_IP2)    := MM_int_req(2);
+      newCAUSE(CAUSE_IP1)    := CAUSE(CAUSE_IP1);
+      newCAUSE(CAUSE_IP0)    := CAUSE(CAUSE_IP0);
+      newCAUSE(7)            := '0';
+      newCAUSE(6 downto 2)   := ExcCode;
+      newCAUSE(1 downto 0)   := b"00";
     else
-      newCAUSE(CAUSE_BD)   := CAUSE(CAUSE_BD);  -- hold it on a double fault
+      newCAUSE               := CAUSE;  -- hold it on an exception
     end if;
-    newCAUSE(CAUSE_TI)     := count_eq_compare;
-    newCAUSE(CAUSE_CE1)    := '0';
-    newCAUSE(CAUSE_CE0)    := '0';
-    newCAUSE(CAUSE_DC)     := CAUSE(CAUSE_DC);
-    newCAUSE(CAUSE_PCI)    := '0';
-    newCAUSE(25 downto 24) := b"00";
-    newCAUSE(CAUSE_IV)     := CAUSE(CAUSE_IV);
-    newCAUSE(CAUSE_WP)     := '0';
-    newCAUSE(21 downto 16) := b"000000";      
-    newCAUSE(CAUSE_IP7)    := MM_int_req(7);
-    newCAUSE(CAUSE_IP6)    := MM_int_req(6);
-    newCAUSE(CAUSE_IP5)    := MM_int_req(5);
-    newCAUSE(CAUSE_IP4)    := MM_int_req(4);
-    newCAUSE(CAUSE_IP3)    := MM_int_req(3);
-    newCAUSE(CAUSE_IP2)    := MM_int_req(2);
-    newCAUSE(CAUSE_IP1)    := CAUSE(CAUSE_IP1);
-    newCAUSE(CAUSE_IP0)    := CAUSE(CAUSE_IP0);
-    newCAUSE(7)            := '0';
-    newCAUSE(6 downto 2)   := ExcCode;
-    newCAUSE(1 downto 0)   := b"00";
 
     if (update = '1' and update_reg = cop0reg_CAUSE) then
       CAUSEinp <= newCAUSE(CAUSE_BD downto CAUSE_CE0) &
@@ -2365,22 +2365,9 @@ begin
     end if;
   end process COP0_COMPUTE_CAUSE;
 
-  COP0_CAUSE_HOLD: process(rst,clk, ExcCode,is_exception,
-                           MM_cop0_reg,not_stalled)
-    variable state: reg32;
-  begin
-    if rst = '0' then                   -- hold CAUSE until it is read
-      cause_update <= '0';
-    elsif ( rising_edge(clk) and (ExcCode /= cop0code_NULL) ) then
-      cause_update <= '1';              -- syscall/trap/interrupt/exception
-    elsif ( rising_edge(clk) and (is_exception = exMFC0) and
-            MM_cop0_reg = cop0reg_CAUSE and (not_stalled = '1') ) then
-        cause_update <= '0';            -- CAUSE is being read
-    end if;
-  end process COP0_CAUSE_HOLD;
-
+ 
   COP0_CAUSE: register32 generic map (RESET_CAUSE)
-    port map (clk, rst, cause_update, CAUSEinp, CAUSE);
+    port map (clk, rst, '0', CAUSEinp, CAUSE);
 
 
   -- EPC -- pg 97 -- cop0_14 -------------------
@@ -2418,8 +2405,7 @@ begin
   COP0_COUNT_INTERRUPT: FFD
     port map (clk, rst, '1', compare_set, count_eq_compare);
   
-  disable_count <= CAUSE(CAUSE_DC)
-                   when (cause_update='0' and CAUSE(CAUSE_DC) /= count_enable)
+  disable_count <= CAUSE(CAUSE_DC) when (CAUSE(CAUSE_DC) /= count_enable)
                    else count_enable;     -- load new CAUSE(CAUSE_DC)
   COP0_DISABLE_COUNT: FFD port map (clk,'1',rst, disable_count, count_enable);