Made execute unit start at a state transition of a signal from the decoder thus allowing for an IPC of 0.99 !!

system/decoder.v

@@ -107,7 +107,7 @@ wire [`UCODE_DATA_BITS-1:0] ucode_data;
 
 microcode ucode(seq_addr_input,ucode_data);
 
-`define invalid_instruction next_state=`EXEC_DONE;ERROR<=`ERR_UNIMPL_INSTRUCTION;IN_MOD=3'b011;seq_addr_entry<=`UCODE_NO_INSTRUCTION;
+`define invalid_instruction next_state=`EXEC_WAIT;ERROR<=`ERR_UNIMPL_INSTRUCTION;IN_MOD=3'b011;seq_addr_entry<=`UCODE_NO_INSTRUCTION;
 
 
 //TODO: A possible optimisation for instruction with 8bit parameter and
@@ -362,7 +362,7 @@ always @( FLAGS or CIR or SIMPLE_MICRO or seq_addr_input ) begin
 				ERROR<=`ERR_NO_ERROR;
 				MEM_OR_IO=0;
 				seq_addr_entry<=`UCODE_NO_INSTRUCTION;
-				next_state=`EXEC_HALT;
+				next_state=`EXEC_WAIT;
 				DEPENDS_ON_PREVIOUS<=0;
 				memio_address_select=0;
 			end

system/exec_state_def.v

@@ -21,9 +21,7 @@
 `define	EXEC_STATE_BITS	4
 
 
-`define EXEC_HALT				4'b0000
+`define EXEC_WAIT				4'b1100
-
-`define EXEC_DONE				4'b1100
 
 /*DECODE SATE*/
 `define EXEC_DE_LOAD_16_PARAM			4'b0010

system/execute.v

@@ -69,14 +69,12 @@ ALU ALU1(
 
 /*############ Execute logic ########################################################## */
 
-always @(posedge valid_input) begin
+always @(valid_input) begin
-	if(exec_state == `EXEC_DONE) begin
 	exec_state <= init_state;
 	reg_write_we <= 1;
 	biu_jump_req <= 0;
 	use_exec_reg_addr <= 0;
 end
-end
 
 always @( set_initial_values) begin
 	PARAM1 <= PARAM1_INIT;
@@ -84,14 +82,16 @@ always @( set_initial_values) begin
 end
 
 always @(negedge reset) begin
-	exec_state <= `EXEC_HALT;
+	exec_state <= `EXEC_WAIT;
 end
 
 always @(posedge reset) begin
 	exec_state <= `EXEC_RESET;
 end
 
-`define unimpl_addressing_mode exec_state <= `EXEC_DONE;ERROR <= `ERR_UNIMPL_ADDRESSING_MODE;
+`define unimpl_addressing_mode exec_state <= `EXEC_WAIT;ERROR <= `ERR_UNIMPL_ADDRESSING_MODE;
+
+`define finished_instruction next_exec<=!next_exec; exec_state <= `EXEC_WAIT;
 
 always @(posedge clock) begin
 	case (exec_state)
@@ -101,16 +101,13 @@ always @(posedge clock) begin
 			biu_data_direction <= 0;
 			biu_jump_req <= 0;
 			reg_write_we <= 1;
-			exec_state <= `EXEC_DONE;
+			exec_state <= `EXEC_WAIT;
 			next_exec <= 0;
 			ERROR <= `ERR_NO_ERROR;
 		end
-		`EXEC_DONE:begin
+		`EXEC_WAIT:begin
 			reg_write_we <= 1;
 			use_exec_reg_addr <= 0;
-			if(valid_input)begin
-				exec_state <= init_state;
-			end
 		end
 		`EXEC_DE_LOAD_REG_TO_PARAM:begin
 			PARAM2<=reg_read_port2_data;
@@ -235,9 +232,8 @@ always @(posedge clock) begin
 			end
 		end
 		`EXEC_NEXT_INSTRUCTION:begin
-			next_exec <= !next_exec;
+			`finished_instruction
 			/*necessary for biu to see we went on another state from decode to give us a new instruction*/
-			exec_state <= `EXEC_DONE;
 		end
 		`EXEC_WRITE_ENTRY:begin
 			FLAGS[7:0] <= ALU_FLAGS[7:0];
@@ -291,12 +287,10 @@ always @(posedge clock) begin
 				end
 				3'b011:begin
 					reg_write_we <= 0;
-					exec_state <= `EXEC_DONE;
+					`finished_instruction
-					next_exec <= !next_exec;
 				end
 				3'b100:begin /*No output*/
-					exec_state <= `EXEC_DONE;
+					`finished_instruction
-					next_exec <= !next_exec;
 				end
 				3'b101:begin /* Program Counter*/
 					BIU_ADDRESS_INPUT <= ALU_O[15:0];
@@ -310,8 +304,7 @@ always @(posedge clock) begin
 				end
 				3'b111:begin /* Write to PRAM1 (for microcode calculations) */
 					PARAM1 <= ALU_O;
-					exec_state <= `EXEC_DONE;
+					`finished_instruction
-					next_exec <= !next_exec;
 				end
 				default:begin
 					`unimpl_addressing_mode
@@ -320,8 +313,7 @@ always @(posedge clock) begin
 		end
 		`EXEC_JUMP_RELEASE:begin
 			biu_jump_req <= 0;
-			exec_state <= `EXEC_DONE;
+			`finished_instruction
-			next_exec <= !next_exec;
 		end
 		`EXEC_MEMIO_WRITE:begin
 			/* if memio_address_select == 0  ADDRESS: reg_read_port1_data   DATA:ALU1_O */
@@ -336,12 +328,9 @@ always @(posedge clock) begin
 
 			if (write == 0) begin //TODO: don't do it that was or better yet don't do it at all somehow
 				biu_write_request <= 0;
-				exec_state <= `EXEC_DONE;
+				`finished_instruction
-				next_exec <= !next_exec;
 			end
 
-		end
-		`EXEC_HALT:begin
 		end
 		default:begin
 		end

system/processor.v

@@ -227,10 +227,9 @@ always @(next_exec) begin
 		ProgCount <= INSTRUCTION_LOCATION+{12'b0,instr_end};
 		INSTRUCTION_BUFFER<=INSTRUCTION[23:0];
 		wait_exec<=1;
-		valid_exec_data<=1;
+		valid_exec_data<=!valid_exec_data;
 	end else begin
 		wait_exec<=0;
-		valid_exec_data<=0;
 	end
 end
 
@@ -246,6 +245,7 @@ always @(posedge clock) begin
 			owe_set_init <= 0;
 			set_initial_values<=0;
 			wait_exec<=0;
+			valid_exec_data<=0;
 		end
 		`PROC_DE_STATE_ENTRY:begin
 			if( VALID_INSTRUCTION==1 || SIMPLE_MICRO == 1 ) begin
@@ -274,7 +274,7 @@ always @(posedge clock) begin
 						/*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 <= 1;
+						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
@@ -284,15 +284,6 @@ always @(posedge clock) begin
 						end
 						wait_exec<=1;
 					end
-				end else begin
-					if( DE_DEPENDS_ON_PREVIOUS == 0 )
-						if ( (ucode_seq_addr==`UCODE_NO_INSTRUCTION) && (ucode_seq_addr_entry!=`UCODE_NO_INSTRUCTION) && valid_exec_data==0 )begin
-							/*switch to microcode decoding*/
-							ucode_seq_addr <= ucode_seq_addr_entry;
-							SIMPLE_MICRO <= 1;
-							owe_set_init <= 1;
-							/*keep proc_state the same and rerun decode this time with all the data from the microcode rom*/
-						end
 				end
 			end
 		end
@@ -304,7 +295,7 @@ always @(posedge clock) begin
 end
 
 always @(exec_state) begin
-	if(exec_state == `EXEC_DONE)
+	if(exec_state == `EXEC_WAIT)
 		FLAGS <= {8'b0,EXEC_FLAGS}; //TODO: don't set all of them all the time!
 end