Merge pull request #29 from antonblanchard/no-second-write-port

Remove second write port

common.vhdl

@@ -128,11 +128,8 @@ package common is
 		write_enable: std_ulogic;
 		write_reg : std_ulogic_vector(4 downto 0);
 		write_data : std_ulogic_vector(63 downto 0);
-		write_enable2: std_ulogic;
-		write_reg2 : std_ulogic_vector(4 downto 0);
-		write_data2 : std_ulogic_vector(63 downto 0);
 	end record;
-	constant Loadstore2ToWritebackInit : Loadstore2ToWritebackType := (valid => '0', write_enable => '0', write_enable2 => '0', others => (others => '0'));
+	constant Loadstore2ToWritebackInit : Loadstore2ToWritebackType := (valid => '0', write_enable => '0', others => (others => '0'));
 
 	type Execute1ToExecute2Type is record
 		valid: std_ulogic;

loadstore2.vhdl

@@ -86,6 +86,17 @@ begin
 					if l_in.load = '1' then
 						m_tmp.we <= '0';
 
+						-- Load with update instructions write two GPR destinations.
+						-- We don't want the expense of two write ports, so make it
+						-- single in the pipeline and write back the update GPR now
+						-- and the load once we get the data back. We'll have to
+						-- revisit this when loads can take exceptions.
+						if l_in.update = '1' then
+							w_tmp.write_enable <= '1';
+							w_tmp.write_reg <= l_in.update_reg;
+							w_tmp.write_data <= l_in.addr;
+						end if;
+
 						state <= WAITING_FOR_READ_ACK;
 					else
 						m_tmp.we <= '1';
@@ -135,12 +146,6 @@ begin
 					w_tmp.write_enable <= '1';
 					w_tmp.write_reg <= l_saved.write_reg;
 
-					if l_saved.update = '1' then
-						w_tmp.write_enable2 <= '1';
-						w_tmp.write_reg2 <= l_saved.update_reg;
-						w_tmp.write_data2 <= l_saved.addr;
-					end if;
-
 					m_tmp <= wishbone_master_out_init;
 					state <= IDLE;
 				end if;

writeback.vhdl

@@ -48,7 +48,6 @@ begin
 		w_tmp <= WritebackToRegisterFileInit;
 		c_tmp <= WritebackToCrFileInit;
 
-		if e.valid = '1' then
 		if e.write_enable = '1' then
 			w_tmp.write_reg <= e.write_reg;
 			w_tmp.write_data <= e.write_data;
@@ -60,30 +59,23 @@ begin
 			c_tmp.write_cr_mask <= e.write_cr_mask;
 			c_tmp.write_cr_data <= e.write_cr_data;
 		end if;
-		end if;
 
-		if l.valid = '1' and l.write_enable = '1' then
+		if l.write_enable = '1' then
 			w_tmp.write_reg <= l.write_reg;
 			w_tmp.write_data <= l.write_data;
 			w_tmp.write_enable <= '1';
 		end if;
-		if l.valid = '1' and l.write_enable2 = '1' then
-			w_tmp.write_reg2 <= l.write_reg2;
-			w_tmp.write_data2 <= l.write_data2;
-			w_tmp.write_enable2 <= '1';
-		end if;
 
-		if m.valid = '1' then
 		if m.write_reg_enable = '1' then
 			w_tmp.write_enable <= '1';
 			w_tmp.write_reg <= m.write_reg_nr;
 			w_tmp.write_data <= m.write_reg_data;
 		end if;
+
 		if m.write_cr_enable = '1' then
 			c_tmp.write_cr_enable <= '1';
 			c_tmp.write_cr_mask <= m.write_cr_mask;
 			c_tmp.write_cr_data <= m.write_cr_data;
 		end if;
-		end if;
 	end process;
 end;