Fetch: Rewrite to be cleaner.

diff --git a/Fetch.v b/Fetch.v
index 7dd4bb02aa207f9ff3fd976ffcab86dab1ddefef..5255647c529bc926692175c7ad93f75744d76e01 100644 (file)
--- a/Fetch.v
+++ b/Fetch.v
@@ -12,37 +12,49 @@ module Fetch(
        input [31:0] jmppc,
        output reg bubble = 1,
        output reg [31:0] insn = 0,
        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 @(*)     
-               if (!Nrst)
-                       nextpc = 32'hFFFFFFFC;
-               else if (stall) /* don't change any internal state */
-                       nextpc = prevpc;
+       output reg [31:0] pc = 32'hFFFFFFFC);
+       
+       reg qjmp = 0;   /* A jump has been queued up while we were stalled. */
+       reg [31:0] qjmppc;
+       always @(posedge clk)
+               if (stall && jmp && !qjmp)
+                       {qjmp,qjmppc} <= {jmp, jmppc};
+               else if (!stall && qjmp)        /* It has already been handled. */
+                       {qjmp,qjmppc} <= {1'b0, 32'hxxxxxxxx};
+       
+       reg [31:0] reqpc;
+       always @(*)
+               if (stall)
+                       reqpc = pc;
+               else if (qjmp)
+                       reqpc = qjmppc;

                else if (jmp)
                else if (jmp)

-                       nextpc = jmppc;
+                       reqpc = jmppc;

                else
                else

-                       nextpc = prevpc + 32'h4;
+                       reqpc = pc + 4;
+       
+       assign rd_addr = reqpc;
+       assign rd_req = 1;
+       
+       always @(negedge Nrst)
+       begin
+               pc <= 32'hFFFFFFFC;
+               qjmp <= 0;
+               bubble <= 1;
+       end

        
        

-       assign rd_addr = nextpc;
-       assign rd_req = !stall;
-                       

        always @(posedge clk)
        begin
        always @(posedge clk)
        begin

-               if (!rd_wait || !Nrst)
-                       prevpc <= nextpc;
-               if (!stall)
+               if (!Nrst) begin
+                       pc <= 32'hFFFFFFFC;
+                       qjmp <= 0;
+                       bubble <= 1;
+               end else if (!stall)

                begin
                        bubble <= rd_wait;
                        insn <= rd_data;
                begin
                        bubble <= rd_wait;
                        insn <= rd_data;

-                       pc <= nextpc;
+                       if (!rd_wait)
+                               pc <= reqpc;

                end
        end
 endmodule
                end
        end
 endmodule