From d2a98c02ff2a9086907a028f15d8271ee4bbd6d9 Mon Sep 17 00:00:00 2001
From: "(Tim) Efthimis Kritikos" <efkf@firemail.cc>
Date: Sat, 27 May 2023 17:59:52 +0100
Subject: [PATCH] Removed duplicate code and improved microcode entry

---
 system/processor.v | 86 +++++++++++++++++++++-------------------------
 1 file changed, 40 insertions(+), 46 deletions(-)

diff --git a/system/processor.v b/system/processor.v
index 39953c2..f62b6e4 100644
--- a/system/processor.v
+++ b/system/processor.v
@@ -198,7 +198,10 @@ always @(negedge reset) begin
 end
 always @(posedge reset) begin
 	proc_state <= `PROC_RESET;
-	valid_instruction_ack <= 0; // needs early init
+	/* need early init */
+	valid_instruction_ack <= 0;
+	instant_response <= 0;
+	stalled_response <= 0;
 end
 
 /*** Processor stages ***/
@@ -216,29 +219,55 @@ reg owe_set_init;
 reg VALID_INSTRUCTION_lc;
 always @(VALID_INSTRUCTION)begin VALID_INSTRUCTION_lc<=VALID_INSTRUCTION; end
 
+reg instant_response, stalled_response;
+reg wait_exec;
+
 always @(next_exec) begin
 	proc_state<=`PROC_DE_STATE_ENTRY;
-	if ( VALID_INSTRUCTION_lc == 1  && SIMPLE_MICRO == 0 && DE_DEPENDS_ON_PREVIOUS == 0 && ucode_seq_addr_entry==`UCODE_NO_INSTRUCTION) begin
+	if ( VALID_INSTRUCTION_lc == 1 && DE_DEPENDS_ON_PREVIOUS == 0 && ucode_seq_addr_entry==`UCODE_NO_INSTRUCTION) begin
+		instant_response <= !instant_response;
+	end else begin
+		wait_exec<=0;
+	end
+end
+
+always @(instant_response or stalled_response) begin
+	DE_OUTPUT_sampled <= DE_OUTPUT;
+
+	if(SIMPLE_MICRO==0||owe_set_init==1)begin
+		/* This runs at the start of the execution of an 8086 instruction */
 		`ifdef DEBUG_PC_ADDRESS
 			$display("Running command at %04x (%08x)",INSTRUCTION_LOCATION,INSTRUCTION);
 		`endif
 		`ifdef CALCULATE_IPC
 			new_instruction <= !new_instruction;
 		`endif
-		DE_OUTPUT_sampled <= DE_OUTPUT;
-		set_initial_values<= !set_initial_values;
 		valid_instruction_ack <= !valid_instruction_ack;
+		owe_set_init<=0;
+		set_initial_values<= !set_initial_values;
 		ProgCount <= INSTRUCTION_LOCATION+{12'b0,instr_end};
 		INSTRUCTION_BUFFER<=INSTRUCTION[23:0];
-		wait_exec<=1;
-		valid_exec_data<=!valid_exec_data;
+	end
+
+	if ( (ucode_seq_addr==`UCODE_NO_INSTRUCTION) && (ucode_seq_addr_entry!=`UCODE_NO_INSTRUCTION) )begin
+		/* switch to microcode decoding */
+		ucode_seq_addr <= ucode_seq_addr_entry;
+		SIMPLE_MICRO <= 1;
+		/*keep proc_state the same and rerun decode this time with all the data from the microcode rom*/
 	end else begin
-		wait_exec<=0;
+		/* This runs at the start of each execution cycle, with microcode this is more than once per 8086 instruction */
+		valid_exec_data<=!valid_exec_data;
+		if( SIMPLE_MICRO == 1 ) begin
+			ucode_seq_addr <= ucode_seq_addr_entry; /*Reused for next address*/
+			if( ucode_seq_addr_entry == `UCODE_NO_INSTRUCTION )begin
+				/*Finished microcode*/
+				SIMPLE_MICRO <= 0;
+			end
+		end
+		wait_exec<=1;
 	end
 end
 
-reg wait_exec;
-
 always @(posedge clock) begin
 	case(proc_state)
 		`PROC_RESET:begin
@@ -252,43 +281,8 @@ always @(posedge clock) begin
 			valid_exec_data<=0;
 		end
 		`PROC_DE_STATE_ENTRY:begin
-			if( VALID_INSTRUCTION==1 || SIMPLE_MICRO == 1 ) begin
-				if(wait_exec==0) begin
-					DE_OUTPUT_sampled <= DE_OUTPUT;
-
-					if(SIMPLE_MICRO==0||owe_set_init==1)begin
-						/* This runs at the start of the execution of an 8086 instruction */
-						`ifdef DEBUG_PC_ADDRESS
-							$display("Running command at %04x (%08x)",INSTRUCTION_LOCATION,INSTRUCTION);
-						`endif
-						`ifdef CALCULATE_IPC
-							new_instruction <= !new_instruction;
-						`endif
-						valid_instruction_ack <= !valid_instruction_ack;
-						owe_set_init<=0;
-						set_initial_values<= !set_initial_values;
-						ProgCount <= INSTRUCTION_LOCATION+{12'b0,instr_end};
-						INSTRUCTION_BUFFER<=INSTRUCTION[23:0];
-					end
-
-					if ( (ucode_seq_addr==`UCODE_NO_INSTRUCTION) && (ucode_seq_addr_entry!=`UCODE_NO_INSTRUCTION) )begin
-						/* switch to microcode decoding */
-						ucode_seq_addr <= ucode_seq_addr_entry;
-						SIMPLE_MICRO <= 1;
-						/*keep proc_state the same and rerun decode this time with all the data from the microcode rom*/
-					end else begin
-						/* This runs at the start of each execution cycle, with microcode this is more than once per 8086 instruction */
-						valid_exec_data<=!valid_exec_data;
-						if( SIMPLE_MICRO == 1 ) begin
-							ucode_seq_addr <= ucode_seq_addr_entry; /*Reused for next address*/
-							if( ucode_seq_addr_entry == `UCODE_NO_INSTRUCTION )begin
-								/*Finished microcode*/
-								SIMPLE_MICRO <= 0;
-							end
-						end
-						wait_exec<=1;
-					end
-				end
+			if ( ( VALID_INSTRUCTION==1 || SIMPLE_MICRO == 1 ) && wait_exec==0) begin
+				stalled_response <= !stalled_response;
 			end
 		end
 		`PROC_HALT:begin