some work on cache filling, and fleshing out a bus interface

[firearm.git] / icache.v

diff --git a/icache.v b/icache.v
index c09159f..2c29a6c 100644 (file)
--- a/icache.v
+++ b/icache.v
@@ -2,10 +2,23 @@
 
 module ICache(
        input clk,
 
 module ICache(
        input clk,

+       
+       /* ARM core interface */

        input [31:0] rd_addr,
        input rd_req,
        output reg rd_wait,
        input [31:0] rd_addr,
        input rd_req,
        output reg rd_wait,

-       output reg [31:0] rd_data);
+       output reg [31:0] rd_data,
+       
+       /* bus interface */
+       output reg bus_req,
+       input bus_ack,
+       output reg [31:0] bus_addr,
+       input [31:0] bus_data
+       output reg bus_rd,
+       output wire bus_wr,
+       input bus_ready);
+       
+       assign bus_wr = 0;

        
        /* [31 tag 10] [9 cache index 6] [5 data index 0]
         * so the data index is 6 bits long
        
        /* [31 tag 10] [9 cache index 6] [5 data index 0]
         * so the data index is 6 bits long


@@ -26,8 +39,21 @@ module ICache(
        wire [3:0] rd_idx = rd_addr[9:6];
        wire [21:0] rd_tag = rd_addr[31:10];
        
        wire [3:0] rd_idx = rd_addr[9:6];
        wire [21:0] rd_tag = rd_addr[31:10];
        

+       wire cache_hit = cache_valid[rd_idx] && (cache_tags[rd_idx] == rd_tag);
+       

        always @(*) begin       /* XXX does this work nowadays? */
        always @(*) begin       /* XXX does this work nowadays? */

-               rd_wait = !(cache_valid[rd_idx] && (cache_tags[rd_idx] == rd_tag));
+               rd_wait = !cache_hit;

                rd_data = cache_data[rd_idx][rd_didx_word];
        end
                rd_data = cache_data[rd_idx][rd_didx_word];
        end

+       
+       reg [3:0] cache_fill_pos = 0;
+       reg cache_filling = 0;
+       always @(*) begin
+               if (!cache_hit) begin
+                       bus_req = 1;
+                       if (bus_ack) begin
+                               bus_addr = {rd_addr[31:6], cache_fill_pos[3:0], 2'b00 /* reads are 32-bits */};
+                               bus_rd = 1;
+                       end
+               end

 endmodule
 endmodule