X-Git-Url: http://git.joshuawise.com/fpgaboy.git/blobdiff_plain/e7fb589a21ee26ad897e03cbd0d7a647d9cd97e5..49c326da841985a8aa48e8544173e5c045c6e0eb:/GBZ80Core.v?ds=inline

diff --git a/GBZ80Core.v b/GBZ80Core.v
index 1182b32..e1aa308 100644
--- a/GBZ80Core.v
+++ b/GBZ80Core.v
@@ -146,9 +146,12 @@
 
 module GBZ80Core(
 	input clk,
-	output reg [15:0] busaddress,	/* BUS_* is latched on STATE_FETCH. */
-	inout [7:0] busdata,
-	output reg buswr, output reg busrd,
+	inout [15:0] bus0address,	/* BUS_* is latched on STATE_FETCH. */
+	inout [7:0] bus0data,
+	inout bus0wr, bus0rd,
+	inout [15:0] bus1address,	/* BUS_* is latched on STATE_FETCH. */
+	inout [7:0] bus1data,
+	inout bus1wr, bus1rd,
 	input irq, input [7:0] jaddr,
 	output reg [1:0] state);
 
@@ -167,7 +170,28 @@ module GBZ80Core(
 	reg [7:0] tmp, tmp2;			/* Generic temporary regs. */
 	
 	reg [7:0] buswdata;
-	assign busdata = buswr ? buswdata : 8'bzzzzzzzz;
+	wire [7:0] busdata;
+	
+	reg [15:0] busaddress;
+	reg buswr, busrd;
+	
+	reg bootstrap_enb;
+	
+	wire bus = ((busaddress[15:8] == 8'h00) && bootstrap_enb) || ((busaddress[15:7] == 9'b111111111) && (busaddress != 16'hFFFF))	/* 0 or 1 depending on which bus */
+		`ifdef isim
+			|| (busaddress === 16'hxxxx) /* To avoid simulator glomulation. */
+		`endif
+			;
+		
+	assign bus0address = (bus == 0) ? busaddress : 16'bzzzzzzzzzzzzzzz;
+	assign bus1address = (bus == 1) ? busaddress : 16'bzzzzzzzzzzzzzzz;
+	assign bus0data = ((bus == 0) && buswr) ? buswdata : 8'bzzzzzzzz;
+	assign bus1data = ((bus == 1) && buswr) ? buswdata : 8'bzzzzzzzz;
+	assign busdata = (bus == 0) ? bus0data : bus1data;
+	assign bus0rd = (bus == 0) ? busrd : 1'b0;
+	assign bus1rd = (bus == 1) ? busrd : 1'b0;
+	assign bus0wr = (bus == 0) ? buswr : 1'b0;
+	assign bus1wr = (bus == 1) ? buswr : 1'b0;
 
 	reg ie, iedelay;
 
@@ -257,9 +281,10 @@ module GBZ80Core(
 		state <= `STATE_WRITEBACK;
 		cycle <= 0;
 		twobyte <= 0;
+		bootstrap_enb <= 1;
 	end
 
-	always @(posedge clk)
+	always @(negedge clk)	/* Set things up at the negedge to prepare for the posedge. */
 		case (state)
 		`STATE_FETCH: begin
 			if (newcycle) begin
@@ -273,6 +298,17 @@ module GBZ80Core(
 				if (wr)
 					buswdata <= wdata;
 			end
+		end
+		`STATE_DECODE: begin	/* Make sure this only happens for one clock. */
+			buswr <= 0;
+			busrd <= 0;
+		end
+		endcase
+	
+	always @(posedge clk)
+		case (state)
+		`STATE_FETCH: begin
+			/* Things are set up in negedge so that something looking on posedge will get his shit. */
 			state <= `STATE_DECODE;
 		end
 		`STATE_DECODE: begin
@@ -284,19 +320,17 @@ module GBZ80Core(
 					opcode <= `INSN_VOP_INTR;
 				else
 					opcode <= {1'b0,busdata};
-				rdata <= busdata;
 				newcycle <= 0;
+				rdata <= busdata;
 				cycle <= 0;
 			end else begin
-				if (rd) rdata <= busdata;
+				if (rd) rdata <= busdata;	/* Still valid because peripherals are now expected to keep it held valid. */
 				cycle <= cycle + 1;
 			end
 			if (iedelay) begin
 				ie <= 1;
 				iedelay <= 0;
 			end
-			buswr <= 0;
-			busrd <= 0;
 			wr <= 0;
 			rd <= 0;
 			address <= 16'bxxxxxxxxxxxxxxxx;	// Make it obvious if something of type has happened.
@@ -304,6 +338,8 @@ module GBZ80Core(
 			state <= `STATE_EXECUTE;
 		end
 		`STATE_EXECUTE: begin
+			if (opcode[7:0] === 8'bxxxxxxxx)
+				$stop;
 			casex (opcode)
 			`define EXECUTE
 			`include "allinsns.v"