ICache, Fetch: Re-pipe things such that the icache now has a one-cycle latency. ...
authorJoshua Wise <joshua@escape.joshuawise.com>
Mon, 22 Feb 2010 07:20:36 +0000 (02:20 -0500)
committerJoshua Wise <joshua@escape.joshuawise.com>
Mon, 22 Feb 2010 07:20:36 +0000 (02:20 -0500)
Fetch.v
ICache.v
system.v

diff --git a/Fetch.v b/Fetch.v
index 4dbe365..fc4d899 100644 (file)
--- a/Fetch.v
+++ b/Fetch.v
@@ -5,7 +5,7 @@ module Fetch(
        output wire [31:0] ic__rd_addr_0a,
        output wire        ic__rd_req_0a,
        input              ic__rd_wait_0a,
-       input       [31:0] ic__rd_data_0a,
+       input       [31:0] ic__rd_data_1a,
        
        input              stall_0a,
        input              jmp_0a,
@@ -27,16 +27,33 @@ module Fetch(
        reg [31:0] reqpc_0a;
        
        /* Output latch logic */
+       reg [31:0] insn_2a;
+       reg stall_1a;
+       always @(posedge clk or negedge Nrst)
+               if (!Nrst) begin
+                       insn_2a <= 32'h00000000;
+                       stall_1a <= 0;
+               end else begin
+                       insn_2a <= insn_1a;
+                       stall_1a <= stall_0a;
+               end
+       
+       always @(*)
+               if (stall_1a)
+                       insn_1a = insn_2a;
+               else
+                       insn_1a = ic__rd_data_1a;
+       
        assign ic__rd_addr_0a = reqpc_0a;
        assign ic__rd_req_0a = 1;
+       
+       
        always @(posedge clk or negedge Nrst)
                if (!Nrst) begin
                        bubble_1a <= 1;
-                       insn_1a <= 32'h00000000;
                        pc_1a <= 32'h00000000;
                end else if (!stall_0a) begin
                        bubble_1a <= (jmp_0a || qjmp || ic__rd_wait_0a);
-                       insn_1a <= ic__rd_data_0a;
                        pc_1a <= reqpc_0a;
                end
        
index 2533671..081fc10 100644 (file)
--- a/ICache.v
+++ b/ICache.v
@@ -7,17 +7,17 @@ module ICache(
        input       [31:0] ic__rd_addr_0a,
        input              ic__rd_req_0a,
        output wire        ic__rd_wait_0a,
-       output wire [31:0] ic__rd_data_0a,
+       output wire [31:0] ic__rd_data_1a,
        
        /* bus interface */
-       output wire bus_req,
-       input bus_ack,
-       output reg [31:0] bus_addr,
-       input [31:0] bus_rdata,
+       output wire        bus_req,
+       input              bus_ack,
+       output reg  [31:0] bus_addr,
+       input       [31:0] bus_rdata,
        output wire [31:0] bus_wdata,
-       output reg bus_rd,
-       output wire bus_wr,
-       input bus_ready);
+       output reg         bus_rd,
+       output wire        bus_wr,
+       input              bus_ready);
        
        assign bus_wr = 0;
        assign bus_wdata = 0;
@@ -25,9 +25,9 @@ module ICache(
        wire [31:0] rd_addr_0a;
        wire        rd_req_0a;
        reg         rd_wait_0a;
-       reg  [31:0] rd_data_0a;
+       reg  [31:0] rd_data_1a;
        assign ic__rd_wait_0a = rd_wait_0a;
-       assign ic__rd_data_0a = rd_data_0a;
+       assign ic__rd_data_1a = rd_data_1a;
        assign rd_addr_0a = ic__rd_addr_0a;
        assign rd_req_0a = ic__rd_req_0a;
        
@@ -49,46 +49,47 @@ module ICache(
                        cache_tags[i[3:0]] = 0;
                end
        
-       wire [5:0] rd_didx = rd_addr_0a[5:0];
-       wire [3:0] rd_didx_word = rd_didx[5:2];
-       wire [3:0] rd_idx = rd_addr_0a[9:6];
-       wire [21:0] rd_tag = rd_addr_0a[31:10];
+       wire  [5:0] rd_didx_0a      = rd_addr_0a[5:0];
+       wire  [3:0] rd_didx_word_0a = rd_didx_0a[5:2];
+       wire  [3:0] rd_idx_0a       = rd_addr_0a[9:6];
+       wire [21:0] rd_tag_0a       = rd_addr_0a[31:10];
        
-       reg [31:0] prev_rd_addr = 32'hFFFFFFFF;
+       reg  [31:0] rd_addr_1a = 32'hFFFFFFFF;
        
-       wire cache_hit = cache_valid[rd_idx] && (cache_tags[rd_idx] == rd_tag);
+       wire cache_hit_0a = cache_valid[rd_idx_0a] && (cache_tags[rd_idx_0a] == rd_tag_0a);
        
-       reg [3:0] cache_fill_pos = 0;
-       assign bus_req = rd_req_0a && !cache_hit; /* xxx, needed for Verilator */
+       reg [3:0] cache_fill_pos_0a = 0;
+       assign bus_req = rd_req_0a && !cache_hit_0a; /* xxx, needed for Verilator */
        always @(*)
-               if (rd_req_0a && !cache_hit && bus_ack) begin
-                       bus_addr = {rd_addr_0a[31:6], cache_fill_pos[3:0], 2'b00 /* reads are 32-bits */};
+               if (rd_req_0a && !cache_hit_0a && bus_ack) begin
+                       bus_addr = {rd_addr_0a[31:6], cache_fill_pos_0a[3:0], 2'b00 /* reads are 32-bits */};
                        bus_rd = 1;
                end else begin
                        bus_addr = 0;
                        bus_rd = 0;
                end
 
-       wire [31:0] curdata = cache_data[{rd_idx,rd_didx_word}];
        always @(*) begin
-               rd_wait_0a = rd_req_0a && !cache_hit;
-               rd_data_0a = curdata;
+               rd_wait_0a = rd_req_0a && !cache_hit_0a;
        end
        
        always @(posedge clk) begin
-               prev_rd_addr <= {rd_addr_0a[31:6], 6'b0};
-               if (cache_fill_pos != 0 && ((prev_rd_addr != {rd_addr_0a[31:6], 6'b0}) || cache_hit))   /* If this wasn't from the same line, or we've moved on somehow, reset the fill circuitry. */
-                       cache_fill_pos <= 0;
-               else if (rd_req_0a && !cache_hit && bus_ack && bus_ready) begin
+               // Do the actual read.
+               rd_data_1a <= cache_data[{rd_idx_0a,rd_didx_word_0a}];
+               
+               rd_addr_1a <= {rd_addr_0a[31:6], 6'b0};
+               if (cache_fill_pos_0a != 0 && ((rd_addr_1a != {rd_addr_0a[31:6], 6'b0}) || cache_hit_0a))       /* If this wasn't from the same line, or we've moved on somehow, reset the fill circuitry. */
+                       cache_fill_pos_0a <= 0;
+               else if (rd_req_0a && !cache_hit_0a && bus_ack && bus_ready) begin
                        $display("ICACHE: FILL: rd addr %08x; bus addr %08x; bus data %08x", rd_addr_0a, bus_addr, bus_rdata);
-                       cache_data[{rd_idx,cache_fill_pos}] <= bus_rdata;
-                       cache_fill_pos <= cache_fill_pos + 1;
-                       if (cache_fill_pos == 15) begin /* Done? */
-                               cache_tags[rd_idx] <= rd_tag;
-                               cache_valid[rd_idx] <= 1;
-                               $display("ICACHE: Fill complete for line %x, tag %x", rd_idx, rd_tag);
+                       cache_data[{rd_idx_0a,cache_fill_pos_0a}] <= bus_rdata;
+                       cache_fill_pos_0a <= cache_fill_pos_0a + 1;
+                       if (cache_fill_pos_0a == 15) begin      /* Done? */
+                               cache_tags[rd_idx_0a] <= rd_tag_0a;
+                               cache_valid[rd_idx_0a] <= 1;
+                               $display("ICACHE: Fill complete for line %x, tag %x", rd_idx_0a, rd_tag_0a);
                        end else
-                               cache_valid[rd_idx] <= 0;
+                               cache_valid[rd_idx_0a] <= 0;
                end
        end
 endmodule
index e63e03b..1a5edfe 100644 (file)
--- a/system.v
+++ b/system.v
@@ -114,7 +114,7 @@ module System(input clk, input rst
        /*AUTOWIRE*/
        // Beginning of automatic wires (for undeclared instantiated-module outputs)
        wire [31:0]     ic__rd_addr_0a;         // From fetch of Fetch.v
-       wire [31:0]     ic__rd_data_0a;         // From icache of ICache.v
+       wire [31:0]     ic__rd_data_1a;         // From icache of ICache.v
        wire            ic__rd_req_0a;          // From fetch of Fetch.v
        wire            ic__rd_wait_0a;         // From icache of ICache.v
        // End of automatics
@@ -139,7 +139,7 @@ module System(input clk, input rst
        ICache icache(/*AUTOINST*/
                      // Outputs
                      .ic__rd_wait_0a   (ic__rd_wait_0a),
-                     .ic__rd_data_0a   (ic__rd_data_0a[31:0]),
+                     .ic__rd_data_1a   (ic__rd_data_1a[31:0]),
                      .bus_req          (bus_req_icache),        // Templated
                      .bus_addr         (bus_addr_icache),       // Templated
                      .bus_wdata        (bus_wdata_icache),      // Templated
@@ -196,7 +196,7 @@ module System(input clk, input rst
                    .clk                (clk),                   // Templated
                    .Nrst               (~rst),                  // Templated
                    .ic__rd_wait_0a     (ic__rd_wait_0a),
-                   .ic__rd_data_0a     (ic__rd_data_0a[31:0]),
+                   .ic__rd_data_1a     (ic__rd_data_1a[31:0]),
                    .stall_0a           (stall_cause_issue),     // Templated
                    .jmp_0a             (jmp),                   // Templated
                    .jmppc_0a           (jmppc));                // Templated
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