From d8083946f36dafa37c8ab21c2e2b1fba1d756e01 Mon Sep 17 00:00:00 2001
From: Jens Ahrensfeld <jens@jayfield.org>
Date: Sat, 17 Oct 2009 17:19:41 +0000
Subject: [PATCH] - changed NMI/RST behavior: reset exception entered after
 NMI/RST transition 1 => 0. - BEV = 1 after NMI/RST (like hard reset) - status
 not KUc,IEc not saved to KUp, IEp at NMI/RST (like hard reset) Committed on
 the Free edition of March Hare Software CVSNT Server. Upgrade to CVS Suite
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git-svn-id: http://moon:8086/svn/vhdl/trunk@523 cc03376c-175c-47c8-b038-4cd826a8556b
---
 lib/CPUs/MIPS/src/core/mips_cop.vhd | 101 +++++++++++++++++-----------
 1 file changed, 63 insertions(+), 38 deletions(-)

diff --git a/lib/CPUs/MIPS/src/core/mips_cop.vhd b/lib/CPUs/MIPS/src/core/mips_cop.vhd
index e25970d..79c95d3 100644
--- a/lib/CPUs/MIPS/src/core/mips_cop.vhd
+++ b/lib/CPUs/MIPS/src/core/mips_cop.vhd
@@ -82,6 +82,8 @@ architecture Behavioral of cop is
 	signal reg_wptr			: reg_ptr_t;
 	signal inject_exc		: STD_LOGIC;
 	signal latch_vect_en	: STD_LOGIC;
+	signal int_nmi			: STD_LOGIC;
+	signal nmi_asserted		: std_logic;
 	
 	type cop_pipe_t is record
 		opc			: opcode_t;
@@ -147,7 +149,28 @@ begin
 	eflags.RI		<= ctrl_in.events.illegal;
 	eflags.Int		<= ctrl_in.events.int;
 
-exception_state:
+proc_nmi_state_next:
+	process(clk)
+	begin
+		if rising_edge(clk) then
+			if rst = '1' then
+				int_nmi			<= '0';
+				nmi_asserted	<= '0';
+			elsif latch_vect_en = '1' then
+				int_nmi	<= '0';
+			elsif nmi_asserted = '1' then
+				if nmi = '0' then
+					nmi_asserted	<= '0';
+					int_nmi			<= '1';
+				end if;	
+			elsif nmi = '1' then
+				nmi_asserted	<= '1';
+			end if;	
+		end if;
+	end process;
+
+
+proc_exc_state:
 	process(exc_state, ctrl_in, cop_pipe_ID)
 	begin
 	
@@ -219,6 +242,18 @@ exception_state:
 		end case;
 	end process;	
 
+proc_exc_state_next:
+	process(clk)
+	begin
+		if rising_edge(clk) then
+			if rst = '1' then
+				exc_state <= exc_idle;
+			else
+				exc_state <= exc_staten;
+			end if;	
+		end if;
+	end process;
+
 sample_endian:
 	process(clk)
 	begin
@@ -239,25 +274,13 @@ exception_last_imem_addr:
 		end if;
 	end process;
 
-exception_state_next:
-	process(clk)
-	begin
-		if rising_edge(clk) then
-			if rst = '1' then
-				exc_state <= exc_idle;
-			else
-				exc_state <= exc_staten;
-			end if;	
-		end if;
-	end process;
-
 cop_exception_epc_write:
 	process(clk)
 	begin
 		if rising_edge(clk) then
 			if rst = '1' then
-				bd			<= '0';
-				epc	<= (others => '0');
+				bd		<= '0';
+				epc		<= (others => '0');
 			elsif epc_reg_we = '1' then
 				bd			<= '0';
 				epc			<= ctrl_in.epc_mem;
@@ -349,7 +372,7 @@ cop_ip_reg_write:
 			ipm_v			:= ip_v and im;
 			ip				<= ip_v;
 			ctrl_out.int	<= (eval_int(ipm_v) and status(0));
-			ctrl_out.NMI	<= nmi;
+			ctrl_out.NMI	<= int_nmi;
 		end if;
 	end process;
 
@@ -476,30 +499,32 @@ cop_status_reg_write:
 		if rising_edge(clk) then
 			if rst = '1' then
 				status	<= X"00600000";
-			else
-				if status_save = '1' then
+			elsif status_save = '1' then
+				if ctrl_in.events.nmi = '0' then
 					status(5 downto 4)	<= status(3 downto 2);
 					status(3 downto 2)	<= status(1 downto 0);
-					status(1 downto 0)	<= "00";
-				elsif status_rest = '1' then
-					status(1 downto 0)	<= status(3 downto 2);
-					status(3 downto 2)	<= status(5 downto 4);
-				elsif ctrl_in.sdu.WB_nop = '0' then
-					if stat_reg_we = '1' then
-						if status(1) = '0' then
-							status(0)			<= din(0);	-- IEc
-							status(1)			<= din(1);	-- KUc
-							status(2)			<= din(2);	-- IEp
-							status(3)			<= din(3);	-- KUp
-							status(4)			<= din(4);	-- IEo
-							status(5)			<= din(5);	-- KUo
-						end if;	
-						status(15 downto 8)		<= din(15 downto 8);	-- IM
-						status(22)				<= din(22);				-- BEV
-						status(25)				<= din(25);				-- RE
-					end if;
-				end if;	
-			end if;
+				else	
+					status(22)	<= '1';
+				end if;
+				status(1 downto 0)	<= "00";
+			elsif status_rest = '1' then
+				status(1 downto 0)	<= status(3 downto 2);
+				status(3 downto 2)	<= status(5 downto 4);
+			elsif ctrl_in.sdu.WB_nop = '0' then
+				if stat_reg_we = '1' then
+					if status(1) = '0' then
+						status(0)			<= din(0);	-- IEc
+						status(1)			<= din(1);	-- KUc
+						status(2)			<= din(2);	-- IEp
+						status(3)			<= din(3);	-- KUp
+						status(4)			<= din(4);	-- IEo
+						status(5)			<= din(5);	-- KUo
+					end if;	
+					status(15 downto 8)		<= din(15 downto 8);	-- IM
+					status(22)				<= din(22);				-- BEV
+					status(25)				<= din(25);				-- RE
+				end if;
+			end if;	
 		end if;
 	end process;