Console: Put the core in its own clock domain.
[firearm.git] / Fetch.v
diff --git a/Fetch.v b/Fetch.v
index 3b6d9c5..3f28453 100644 (file)
--- a/Fetch.v
+++ b/Fetch.v
@@ -12,37 +12,43 @@ module Fetch(
        input [31:0] jmppc,
        output reg bubble = 1,
        output reg [31:0] insn = 0,
-       output reg [31:0] pc = 0);
-
-       reg [31:0] prevpc;
-       reg [31:0] nextpc;
-       initial
-               prevpc = 32'hFFFFFFFC;  /* ugh... the first pc we request will be this +4 */
-       always @(negedge Nrst)
-               prevpc <= 32'hFFFFFFFC;
-
-       always @(*)     
+       output reg [31:0] pc = 32'hFFFFFFFC);
+       
+       reg qjmp = 0;   /* A jump has been queued up while we were waiting. */
+       reg [31:0] qjmppc;
+       always @(posedge clk or negedge Nrst)
                if (!Nrst)
-                       nextpc = 32'hFFFFFFFC;
-               else if (stall) /* don't change any internal state */
-                       nextpc = prevpc;
-               else if (jmp)
-                       nextpc = jmppc;
-               else
-                       nextpc = prevpc + 32'h4;
+                       qjmp <= 0;
+               else if ((rd_wait || stall) && jmp)
+                       {qjmp,qjmppc} <= {jmp, jmppc};
+               else if (!rd_wait && !stall && qjmp)    /* It has already been intoed. */
+                       {qjmp,qjmppc} <= {1'b0, 32'hxxxxxxxx};
+       
+       reg [31:0] reqpc;
        
-       assign rd_addr = pc;
-       assign rd_req = !stall;
-                       
-       always @(posedge clk)
-       begin
-               if (!rd_wait || !Nrst)
-                       prevpc <= nextpc;
-               if (!stall)
-               begin
-                       bubble <= rd_wait;
+       /* Output latch logic */
+       assign rd_addr = reqpc;
+       assign rd_req = 1;
+       always @(posedge clk or negedge Nrst)
+               if (!Nrst) begin
+                       bubble <= 1;
+                       insn <= 0;
+                       pc <= 32'h00000000;
+               end else if (!stall) begin
+                       bubble <= (jmp || qjmp || rd_wait);
                        insn <= rd_data;
-                       pc <= nextpc;
+                       pc <= reqpc;
+               end
+       
+       always @(posedge clk or negedge Nrst)
+               if (!Nrst)
+                       reqpc <= 0;
+               else if (!stall && !rd_wait) begin
+                       if (qjmp)
+                               reqpc <= qjmppc;
+                       else if (jmp)
+                               reqpc <= jmppc;
+                       else
+                               reqpc <= reqpc + 4;
                end
-       end
 endmodule
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