Fetch: qjmp is for queueing up jumps while rd_waiting, not while stalled.
[firearm.git] / DCache.v
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6060e535
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1/* 16 cache entries, 64-byte long cache lines */
2
3module DCache(
4 input clk,
5
6 /* ARM core interface */
7 input [31:0] addr,
8 input rd_req,
9 input wr_req,
10 output reg rw_wait,
11 input [31:0] wr_data,
12 output reg [31:0] rd_data,
13
14 /* bus interface */
15 output wire bus_req,
16 input bus_ack,
17 output reg [31:0] bus_addr = 0,
18 input [31:0] bus_rdata,
19 output reg [31:0] bus_wdata,
20 output reg bus_rd = 0,
21 output reg bus_wr = 0,
22 input bus_ready);
23
24 /* [31 tag 10] [9 cache index 6] [5 data index 0]
25 * so the data index is 6 bits long
26 * so the cache index is 4 bits long
27 * so the tag is 22 bits long. c.c
28 */
29
30 reg cache_valid [15:0];
31 reg [21:0] cache_tags [15:0];
32 reg [31:0] cache_data [15:0 /* line */] [15:0 /* word */];
33
34 reg [4:0] i;
35 initial
36 for (i = 0; i < 16; i = i + 1)
37 begin
38 cache_valid[i[3:0]] = 0;
39 cache_tags[i[3:0]] = 0;
40 end
41
42 wire [5:0] didx = addr[5:0];
43 wire [3:0] didx_word = didx[5:2];
44 wire [3:0] idx = addr[9:6];
45 wire [21:0] tag = addr[31:10];
46
47 wire cache_hit = cache_valid[idx] && (cache_tags[idx] == tag);
48
49 always @(*) begin
50 rw_wait = (rd_req && !cache_hit) || (wr_req && (!bus_ack || !bus_ready));
51 rd_data = cache_data[idx][didx_word];
52 end
53
54 reg [3:0] cache_fill_pos = 0;
55 assign bus_req = (rd_req && !cache_hit) || wr_req;
56 always @(*)
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57 begin
58 bus_rd = 0;
59 bus_wr = 0;
60 bus_addr = 0;
61 bus_wdata = 0;
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62 if (rd_req && !cache_hit && bus_ack) begin
63 bus_addr = {addr[31:6], cache_fill_pos[3:0], 2'b00 /* reads are 32-bits */};
64 bus_rd = 1;
65 end else if (wr_req && bus_ack) begin
66 bus_addr = addr;
67 bus_wr = 1;
68 bus_wdata = wr_data;
6060e535 69 end
0e3732b3 70 end
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71
72 always @(posedge clk)
73 if (rd_req && !cache_hit) begin
74 if (bus_ready) begin /* Started the fill, and we have data. */
75 cache_data[idx][cache_fill_pos] <= bus_rdata;
76 cache_fill_pos <= cache_fill_pos + 1;
77 if (cache_fill_pos == 15) begin /* Done? */
78 cache_tags[idx] <= tag;
79 cache_valid[idx] <= 1;
80 end
81 end
82 end else if (wr_req && cache_hit)
83 cache_data[idx][addr[5:2]] = wr_data;
84endmodule
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