Set up the bus a little before the clock.
authorJoshua Wise <joshua@rebirth.joshuawise.com>
Sun, 4 May 2008 07:56:17 +0000 (03:56 -0400)
committerJoshua Wise <joshua@rebirth.joshuawise.com>
Sun, 4 May 2008 07:56:17 +0000 (03:56 -0400)
GBZ80Core.v

index ec882da..b06910a 100644 (file)
@@ -280,7 +280,7 @@ module GBZ80Core(
                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
@@ -294,6 +294,15 @@ module GBZ80Core(
                                if (wr)
                                        buswdata <= wdata;
                        end
+               end
+               `STATE_DECODE: begin    /* Make sure this only happens for one clock. */
+               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
@@ -316,10 +325,10 @@ module GBZ80Core(
                                ie <= 1;
                                iedelay <= 0;
                        end
-                       buswr <= 0;
-                       busrd <= 0;
                        wr <= 0;
                        rd <= 0;
+                       buswr <= 0;
+                       busrd <= 0;
                        address <= 16'bxxxxxxxxxxxxxxxx;        // Make it obvious if something of type has happened.
                        wdata <= 8'bxxxxxxxx;
                        state <= `STATE_EXECUTE;
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