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////////////////////////////////////////////////////////////////////////////////
//
// Filename:    pfcache2.v
//
// Project:     Zip CPU -- a small, lightweight, RISC CPU soft core
//
// Purpose:     Keeping our CPU fed with instructions, at one per clock and
//              with no stalls.  An unusual feature of this cache is the
//      requirement that the entire cache may be cleared (if necessary).
//
// Creator:     Dan Gisselquist, Ph.D.
//              Gisselquist Technology, LLC
//
////////////////////////////////////////////////////////////////////////////////
//
// Copyright (C) 2015, Gisselquist Technology, LLC
//
// This program is free software (firmware): you can redistribute it and/or
// modify it under the terms of  the GNU General Public License as published
// by the Free Software Foundation, either version 3 of the License, or (at
// your option) any later version.
//
// This program is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or
// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
// for more details.
//
// License:     GPL, v3, as defined and found on www.gnu.org,
//              http://www.gnu.org/licenses/gpl.html
//
//
////////////////////////////////////////////////////////////////////////////////
//
module  pfcache(i_clk, i_rst, i_new_pc, i_clear_cache,
                        // i_early_branch, i_from_addr,
                        i_stall_n, i_pc, o_i, o_pc, o_v,
                o_wb_cyc, o_wb_stb, o_wb_we, o_wb_addr, o_wb_data,
                        i_wb_ack, i_wb_stall, i_wb_err, i_wb_data,
                        o_illegal);
        parameter       LGCACHELEN = 8, ADDRESS_WIDTH=24,
                        CACHELEN=(1<<LGCACHELEN), BUSW=32, AW=ADDRESS_WIDTH,
                        CW=LGCACHELEN, PW=LGCACHELEN-5;
        input                           i_clk, i_rst, i_new_pc;
        input                           i_clear_cache;
        input                           i_stall_n;
        input           [(AW-1):0]       i_pc;
        output  reg     [(BUSW-1):0]     o_i;
        output  reg     [(AW-1):0]       o_pc;
        output  wire                    o_v;
        //
        output  reg             o_wb_cyc, o_wb_stb;
        output  wire            o_wb_we;
        output  reg     [(AW-1):0]       o_wb_addr;
        output  wire    [(BUSW-1):0]     o_wb_data;
        //
        input                           i_wb_ack, i_wb_stall, i_wb_err;
        input           [(BUSW-1):0]     i_wb_data;
        //
        output  reg                     o_illegal;
 
        // Fixed bus outputs: we read from the bus only, never write.
        // Thus the output data is ... irrelevant and don't care.  We set it
        // to zero just to set it to something.
        assign  o_wb_we = 1'b0;
        assign  o_wb_data = 0;
 
        reg                     r_v;
        (* ram_style = "distributed" *)
        reg     [(BUSW-1):0]     cache   [0:((1<<CW)-1)];
        reg     [(AW-CW-1):0]    tags    [0:((1<<(CW-PW))-1)];
        reg     [((1<<(CW-PW))-1):0]     vmask;
 
        reg     [(AW-1):0]       lastpc;
        reg     [(CW-1):0]       rdaddr;
        reg     [(AW-1):CW]     tagval;
        reg     [(AW-1):PW]     lasttag, illegal_cache;
 
        initial o_i = 32'h76_00_00_00;  // A NOOP instruction
        initial o_pc = 0;
        always @(posedge i_clk)
                if (~r_v)
                begin
                        o_i <= cache[lastpc[(CW-1):0]];
                        o_pc <= lastpc;
                end else if ((i_stall_n)||(i_new_pc))
                begin
                        o_i <= cache[i_pc[(CW-1):0]];
                        o_pc <= i_pc;
                end
 
        initial tagval = 0;
        always @(posedge i_clk)
                if (i_stall_n)
                        tagval <= tags[i_pc[(CW-1):PW]];
 
        // i_pc will only increment when everything else isn't stalled, thus
        // we can set it without worrying about that.   Doing this enables
        // us to work in spite of stalls.  For example, if the next address
        // isn't valid, but the decoder is stalled, get the next address
        // anyway.
        initial lastpc = 0;
        always @(posedge i_clk)
                if (((r_v)&&(i_stall_n))||(i_clear_cache)||(i_new_pc))
                        lastpc <= i_pc;
 
        initial lasttag = 0;
        always @(posedge i_clk)
                lasttag <= i_pc[(AW-1):PW];
 
        wire    r_v_from_pc, r_v_from_last;
        assign  r_v_from_pc = ((i_pc[(AW-1):PW] == lasttag)
                                &&(tagval == i_pc[(AW-1):CW])
                                &&(vmask[i_pc[(CW-1):PW]]));
        assign  r_v_from_last = ((lastpc[(AW-1):PW] == lasttag)
                                &&(tagval == lastpc[(AW-1):CW])
                                &&(vmask[lastpc[(CW-1):PW]]));
 
        reg     [1:0]    delay;
 
        initial delay = 2'h3;
        initial r_v = 1'b0;
        always @(posedge i_clk)
                if ((i_rst)||(i_clear_cache)||(i_new_pc)||((r_v)&&(i_stall_n)))
                begin
                        r_v <= r_v_from_pc;
                        delay <= 2'h2;
                end else if (~r_v) begin // Otherwise, r_v was true and we were
                        r_v <= r_v_from_last;   // stalled, hence only if ~r_v
                        if (o_wb_cyc)
                                delay <= 2'h2;
                        else if (delay != 0)
                                delay <= delay - 1;
                end
 
        assign  o_v = (r_v)&&(~i_new_pc);
 
 
        initial o_wb_cyc  = 1'b0;
        initial o_wb_stb  = 1'b0;
        initial o_wb_addr = {(AW){1'b0}};
        initial rdaddr    = 0;
        always @(posedge i_clk)
                if ((i_rst)||(i_clear_cache))
                begin
                        o_wb_cyc <= 1'b0;
                        o_wb_stb <= 1'b0;
                end else if (o_wb_cyc)
                begin
                        if ((o_wb_stb)&&(~i_wb_stall))
                        begin
                                if (o_wb_addr[(PW-1):0] == {(PW){1'b1}})
                                        o_wb_stb <= 1'b0;
                                else
                                        o_wb_addr[(PW-1):0] <= o_wb_addr[(PW-1):0]+1;
                        end
 
                        if (i_wb_ack)
                                rdaddr <= rdaddr + 1;
                        if ((rdaddr[(PW-1):0] == {(PW){1'b1}})||(i_wb_err))
                        begin
                                o_wb_cyc <= 1'b0;
                                tags[o_wb_addr[(CW-1):PW]] <= o_wb_addr[(AW-1):CW];
                        end
                        // else if (rdaddr[(PW-1):1] == {(PW-1){1'b1}})
                        //      tags[lastpc[(CW-1):PW]] <= lastpc[(AW-1):CW];
 
                end else if ((~r_v)&&(delay==0)
                        &&((tagval != lastpc[(AW-1):CW])
                                ||(~vmask[lastpc[(CW-1):PW]]))
                        &&(~o_illegal))
                begin
                        o_wb_cyc  <= 1'b1;
                        o_wb_stb  <= 1'b1;
                        o_wb_addr <= { lastpc[(AW-1):PW], {(PW){1'b0}} };
                        rdaddr <= { lastpc[(CW-1):PW], {(PW){1'b0}} };
                end
 
        // Can't initialize an array, so leave cache uninitialized
        always @(posedge i_clk)
                if ((o_wb_cyc)&&(i_wb_ack))
                        cache[rdaddr] <= i_wb_data;
 
        // VMask ... is a section loaded?
        initial vmask = 0;
        always @(posedge i_clk)
                if ((i_rst)||(i_clear_cache))
                        vmask <= 0;
                else if ((~r_v)&&(tagval != lastpc[(AW-1):CW])&&(delay == 0))
                        vmask[lastpc[(CW-1):PW]] <= 1'b0;
                else if ((o_wb_cyc)&&(i_wb_ack)&&(rdaddr[(PW-1):0] == {(PW){1'b1}}))
                        vmask[rdaddr[(CW-1):PW]] <= 1'b1;
 
        reg     illegal_valid;
        initial illegal_cache = 0;
        initial illegal_valid = 0;
        always @(posedge i_clk)
                if ((i_rst)||(i_clear_cache))
                begin
                        illegal_cache <= 0;
                        illegal_valid <= 0;
                end else if ((o_wb_cyc)&&(i_wb_err))
                begin
                        illegal_cache <= lastpc[(AW-1):PW];
                        illegal_valid <= 1'b1;
                end
 
        initial o_illegal = 1'b0;
        always @(posedge i_clk)
                if ((i_rst)||(i_clear_cache))
                        o_illegal <= 1'b0;
                else
                        o_illegal <= (illegal_valid)
                                &&(tagval == i_pc[(AW-1):CW])
                                &&(illegal_cache == i_pc[(AW-1):PW]);
 
endmodule

Line No.	Rev	Author	Line
1	69	dgisselq	`////////////////////////////////////////////////////////////////////////////////`
2			`//`
3			`// Filename: pfcache2.v`
4			`//`
5			`// Project: Zip CPU -- a small, lightweight, RISC CPU soft core`
6			`//`
7			`// Purpose: Keeping our CPU fed with instructions, at one per clock and`
8			`// with no stalls. An unusual feature of this cache is the`
9			`// requirement that the entire cache may be cleared (if necessary).`
10			`//`
11			`// Creator: Dan Gisselquist, Ph.D.`
12			`// Gisselquist Technology, LLC`
13			`//`
14			`////////////////////////////////////////////////////////////////////////////////`
15			`//`
16			`// Copyright (C) 2015, Gisselquist Technology, LLC`
17			`//`
18			`// This program is free software (firmware): you can redistribute it and/or`
19			`// modify it under the terms of the GNU General Public License as published`
20			`// by the Free Software Foundation, either version 3 of the License, or (at`
21			`// your option) any later version.`
22			`//`
23			`// This program is distributed in the hope that it will be useful, but WITHOUT`
24			`// ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or`
25			`// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License`
26			`// for more details.`
27			`//`
28			`// License: GPL, v3, as defined and found on www.gnu.org,`
29			`// http://www.gnu.org/licenses/gpl.html`
30			`//`
31			`//`
32			`////////////////////////////////////////////////////////////////////////////////`
33			`//`
34			`module pfcache(i_clk, i_rst, i_new_pc, i_clear_cache,`
35			`// i_early_branch, i_from_addr,`
36			`i_stall_n, i_pc, o_i, o_pc, o_v,`
37			`o_wb_cyc, o_wb_stb, o_wb_we, o_wb_addr, o_wb_data,`
38			`i_wb_ack, i_wb_stall, i_wb_err, i_wb_data,`
39			`o_illegal);`
40			`parameter LGCACHELEN = 8, ADDRESS_WIDTH=24,`
41			`CACHELEN=(1<<LGCACHELEN), BUSW=32, AW=ADDRESS_WIDTH,`
42			`CW=LGCACHELEN, PW=LGCACHELEN-5;`
43			`input i_clk, i_rst, i_new_pc;`
44			`input i_clear_cache;`
45			`input i_stall_n;`
46			`input [(AW-1):0] i_pc;`
47			`output reg [(BUSW-1):0] o_i;`
48			`output reg [(AW-1):0] o_pc;`
49			`output wire o_v;`
50			`//`
51			`output reg o_wb_cyc, o_wb_stb;`
52			`output wire o_wb_we;`
53			`output reg [(AW-1):0] o_wb_addr;`
54			`output wire [(BUSW-1):0] o_wb_data;`
55			`//`
56			`input i_wb_ack, i_wb_stall, i_wb_err;`
57			`input [(BUSW-1):0] i_wb_data;`
58			`//`
59			`output reg o_illegal;`
60
61			`// Fixed bus outputs: we read from the bus only, never write.`
62			`// Thus the output data is ... irrelevant and don't care. We set it`
63			`// to zero just to set it to something.`
64			`assign o_wb_we = 1'b0;`
65			`assign o_wb_data = 0;`
66
67			`reg r_v;`
68			`(* ram_style = "distributed" *)`
69			`reg [(BUSW-1):0] cache [0:((1<<CW)-1)];`
70			`reg [(AW-CW-1):0] tags [0:((1<<(CW-PW))-1)];`
71			`reg [((1<<(CW-PW))-1):0] vmask;`
72
73			`reg [(AW-1):0] lastpc;`
74			`reg [(CW-1):0] rdaddr;`
75			`reg [(AW-1):CW] tagval;`
76			`reg [(AW-1):PW] lasttag, illegal_cache;`
77
78			`initial o_i = 32'h76_00_00_00; // A NOOP instruction`
79			`initial o_pc = 0;`
80			`always @(posedge i_clk)`
81			`if (~r_v)`
82			`begin`
83			`o_i <= cache[lastpc[(CW-1):0]];`
84			`o_pc <= lastpc;`
85			`end else if ((i_stall_n)\|\|(i_new_pc))`
86			`begin`
87			`o_i <= cache[i_pc[(CW-1):0]];`
88			`o_pc <= i_pc;`
89			`end`
90
91			`initial tagval = 0;`
92			`always @(posedge i_clk)`
93			`if (i_stall_n)`
94			`tagval <= tags[i_pc[(CW-1):PW]];`
95
96			`// i_pc will only increment when everything else isn't stalled, thus`
97			`// we can set it without worrying about that. Doing this enables`
98			`// us to work in spite of stalls. For example, if the next address`
99			`// isn't valid, but the decoder is stalled, get the next address`
100			`// anyway.`
101			`initial lastpc = 0;`
102			`always @(posedge i_clk)`
103	71	dgisselq	`if (((r_v)&&(i_stall_n))\|\|(i_clear_cache)\|\|(i_new_pc))`
104	69	dgisselq	`lastpc <= i_pc;`
105
106			`initial lasttag = 0;`
107			`always @(posedge i_clk)`
108			`lasttag <= i_pc[(AW-1):PW];`
109
110			`wire r_v_from_pc, r_v_from_last;`
111			`assign r_v_from_pc = ((i_pc[(AW-1):PW] == lasttag)`
112			`&&(tagval == i_pc[(AW-1):CW])`
113			`&&(vmask[i_pc[(CW-1):PW]]));`
114			`assign r_v_from_last = ((lastpc[(AW-1):PW] == lasttag)`
115			`&&(tagval == lastpc[(AW-1):CW])`
116			`&&(vmask[lastpc[(CW-1):PW]]));`
117
118			`reg [1:0] delay;`
119
120			`initial delay = 2'h3;`
121			`initial r_v = 1'b0;`
122			`always @(posedge i_clk)`
123	71	dgisselq	`if ((i_rst)\|\|(i_clear_cache)\|\|(i_new_pc)\|\|((r_v)&&(i_stall_n)))`
124	69	dgisselq	`begin`
125			`r_v <= r_v_from_pc;`
126			`delay <= 2'h2;`
127	71	dgisselq	`end else if (~r_v) begin // Otherwise, r_v was true and we were`
128			`r_v <= r_v_from_last; // stalled, hence only if ~r_v`
129	69	dgisselq	`if (o_wb_cyc)`
130			`delay <= 2'h2;`
131			`else if (delay != 0)`
132			`delay <= delay - 1;`
133			`end`
134
135			`assign o_v = (r_v)&&(~i_new_pc);`
136
137
138			`initial o_wb_cyc = 1'b0;`
139			`initial o_wb_stb = 1'b0;`
140			`initial o_wb_addr = {(AW){1'b0}};`
141			`initial rdaddr = 0;`
142			`always @(posedge i_clk)`
143			`if ((i_rst)\|\|(i_clear_cache))`
144			`begin`
145			`o_wb_cyc <= 1'b0;`
146			`o_wb_stb <= 1'b0;`
147			`end else if (o_wb_cyc)`
148			`begin`
149			`if ((o_wb_stb)&&(~i_wb_stall))`
150			`begin`
151			`if (o_wb_addr[(PW-1):0] == {(PW){1'b1}})`
152			`o_wb_stb <= 1'b0;`
153			`else`
154			`o_wb_addr[(PW-1):0] <= o_wb_addr[(PW-1):0]+1;`
155			`end`
156
157			`if (i_wb_ack)`
158			`rdaddr <= rdaddr + 1;`
159			`if ((rdaddr[(PW-1):0] == {(PW){1'b1}})\|\|(i_wb_err))`
160			`begin`
161			`o_wb_cyc <= 1'b0;`
162			`tags[o_wb_addr[(CW-1):PW]] <= o_wb_addr[(AW-1):CW];`
163			`end`
164			`// else if (rdaddr[(PW-1):1] == {(PW-1){1'b1}})`
165			`// tags[lastpc[(CW-1):PW]] <= lastpc[(AW-1):CW];`
166
167			`end else if ((~r_v)&&(delay==0)`
168			`&&((tagval != lastpc[(AW-1):CW])`
169	71	dgisselq	`\|\|(~vmask[lastpc[(CW-1):PW]]))`
170			`&&(~o_illegal))`
171	69	dgisselq	`begin`
172			`o_wb_cyc <= 1'b1;`
173			`o_wb_stb <= 1'b1;`
174			`o_wb_addr <= { lastpc[(AW-1):PW], {(PW){1'b0}} };`
175			`rdaddr <= { lastpc[(CW-1):PW], {(PW){1'b0}} };`
176			`end`
177
178			`// Can't initialize an array, so leave cache uninitialized`
179			`always @(posedge i_clk)`
180			`if ((o_wb_cyc)&&(i_wb_ack))`
181			`cache[rdaddr] <= i_wb_data;`
182
183			`// VMask ... is a section loaded?`
184			`initial vmask = 0;`
185			`always @(posedge i_clk)`
186			`if ((i_rst)\|\|(i_clear_cache))`
187			`vmask <= 0;`
188			`else if ((~r_v)&&(tagval != lastpc[(AW-1):CW])&&(delay == 0))`
189			`vmask[lastpc[(CW-1):PW]] <= 1'b0;`
190			`else if ((o_wb_cyc)&&(i_wb_ack)&&(rdaddr[(PW-1):0] == {(PW){1'b1}}))`
191			`vmask[rdaddr[(CW-1):PW]] <= 1'b1;`
192
193	71	dgisselq	`reg illegal_valid;`
194	69	dgisselq	`initial illegal_cache = 0;`
195	71	dgisselq	`initial illegal_valid = 0;`
196	69	dgisselq	`always @(posedge i_clk)`
197			`if ((i_rst)\|\|(i_clear_cache))`
198	71	dgisselq	`begin`
199	69	dgisselq	`illegal_cache <= 0;`
200	71	dgisselq	`illegal_valid <= 0;`
201			`end else if ((o_wb_cyc)&&(i_wb_err))`
202			`begin`
203	69	dgisselq	`illegal_cache <= lastpc[(AW-1):PW];`
204	71	dgisselq	`illegal_valid <= 1'b1;`
205			`end`
206	69	dgisselq
207			`initial o_illegal = 1'b0;`
208			`always @(posedge i_clk)`
209	71	dgisselq	`if ((i_rst)\|\|(i_clear_cache))`
210			`o_illegal <= 1'b0;`
211			`else`
212			`o_illegal <= (illegal_valid)`
213			`&&(tagval == i_pc[(AW-1):CW])`
214			`&&(illegal_cache == i_pc[(AW-1):PW]);`
215	69	dgisselq
216			`endmodule`

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[/] [zipcpu/] [trunk/] [rtl/] [core/] [pfcache.v] - Blame information for rev 71