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1 /////////////////////////////////////////////////////////////////////
2 //// ////
3 //// Universal FIFO Single Clock ////
4 //// ////
5 //// ////
6 //// Author: Rudolf Usselmann ////
7 //// rudi@asics.ws ////
8 //// ////
9 //// ////
10 //// D/L from: http://www.opencores.org/cores/generic_fifos/ ////
11 //// ////
12 /////////////////////////////////////////////////////////////////////
13 //// ////
14 //// Copyright (C) 2000-2002 Rudolf Usselmann ////
15 //// www.asics.ws ////
16 //// rudi@asics.ws ////
17 //// ////
18 //// This source file may be used and distributed without ////
19 //// restriction provided that this copyright statement is not ////
20 //// removed from the file and that any derivative work contains ////
21 //// the original copyright notice and the associated disclaimer.////
22 //// ////
23 //// THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY ////
24 //// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED ////
25 //// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS ////
26 //// FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL THE AUTHOR ////
27 //// OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, ////
28 //// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES ////
29 //// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE ////
30 //// GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR ////
31 //// BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF ////
32 //// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT ////
33 //// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT ////
34 //// OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE ////
35 //// POSSIBILITY OF SUCH DAMAGE. ////
36 //// ////
37 /////////////////////////////////////////////////////////////////////
38
39 // CVS Log
40 //
41 // $Id: generic_fifo_sc_a.v,v 1.2 2007-02-11 22:21:28 michael Exp $
42 //
43 // $Date: 2007-02-11 22:21:28 $
44 // $Revision: 1.2 $
45 // $Author: michael $
46 // $Locker: $
47 // $State: Exp $
48 //
49 // Change History:
50 // $Log: generic_fifo_sc_a.v,v $
51 // Revision 1.2 2007-02-11 22:21:28 michael
52 // fix address width
53 //
54 // Revision 1.1 2007/02/11 21:58:30 sithglan
55 // += fifo
56 //
57 // Revision 1.1.1.1 2002/09/25 05:42:06 rudi
58 // Initial Checkin
59 //
60 //
61 //
62 //
63 //
64 //
65 //
66 //
67 //
68 //
69 //
70
71 `include "timescale.v"
72
73 /*
74
75 Description
76 ===========
77
78 I/Os
79 ----
80 rst low active, either sync. or async. master reset (see below how to select)
81 clr synchronous clear (just like reset but always synchronous), high active
82 re read enable, synchronous, high active
83 we read enable, synchronous, high active
84 din Data Input
85 dout Data Output
86
87 full Indicates the FIFO is full (combinatorial output)
88 full_r same as above, but registered output (see note below)
89 empty Indicates the FIFO is empty
90 empty_r same as above, but registered output (see note below)
91
92 full_n Indicates if the FIFO has space for N entries (combinatorial output)
93 full_n_r same as above, but registered output (see note below)
94 empty_n Indicates the FIFO has at least N entries (combinatorial output)
95 empty_n_r same as above, but registered output (see note below)
96
97 level indicates the FIFO level:
98 2'b00 0-25% full
99 2'b01 25-50% full
100 2'b10 50-75% full
101 2'b11 %75-100% full
102
103 combinatorial vs. registered status outputs
104 -------------------------------------------
105 Both the combinatorial and registered status outputs have exactly the same
106 synchronous timing. Meaning they are being asserted immediately at the clock
107 edge after the last read or write. The combinatorial outputs however, pass
108 through several levels of logic before they are output. The registered status
109 outputs are direct outputs of a flip-flop. The reason both are provided, is
110 that the registered outputs require quite a bit of additional logic inside
111 the FIFO. If you can meet timing of your device with the combinatorial
112 outputs, use them ! The FIFO will be smaller. If the status signals are
113 in the critical pass, use the registered outputs, they have a much smaller
114 output delay (actually only Tcq).
115
116 Parameters
117 ----------
118 The FIFO takes 3 parameters:
119 dw Data bus width
120 aw Address bus width (Determines the FIFO size by evaluating 2^aw)
121 n N is a second status threshold constant for full_n and empty_n
122 If you have no need for the second status threshold, do not
123 connect the outputs and the logic should be removed by your
124 synthesis tool.
125
126 Synthesis Results
127 -----------------
128 In a Spartan 2e a 8 bit wide, 8 entries deep FIFO, takes 85 LUTs and runs
129 at about 116 MHz (IO insertion disabled). The registered status outputs
130 are valid after 2.1NS, the combinatorial once take out to 6.5 NS to be
131 available.
132
133
134 Misc
135 ----
136 This design assumes you will do appropriate status checking externally.
137
138 IMPORTANT ! writing while the FIFO is full or reading while the FIFO is
139 empty will place the FIFO in an undefined state.
140
141 */
142
143
144 // Selecting Sync. or Async Reset
145 // ------------------------------
146 // Uncomment one of the two lines below. The first line for
147 // synchronous reset, the second for asynchronous reset
148
149 `define SC_FIFO_ASYNC_RESET // Uncomment for Syncr. reset
150 //`define SC_FIFO_ASYNC_RESET or negedge rst // Uncomment for Async. reset
151
152
153 module generic_fifo_sc_a(clk, rst, clr, din, we, dout, re,
154 full, empty, full_r, empty_r,
155 full_n, empty_n, full_n_r, empty_n_r,
156 level);
157
158 parameter dw=8;
159 parameter aw=12;
160 parameter n=32;
161 parameter max_size = 1<<aw;
162
163 input clk, rst, clr;
164 input [dw-1:0] din;
165 input we;
166 output [dw-1:0] dout;
167 input re;
168 output full, full_r;
169 output empty, empty_r;
170 output full_n, full_n_r;
171 output empty_n, empty_n_r;
172 output [1:0] level;
173
174 ////////////////////////////////////////////////////////////////////
175 //
176 // Local Wires
177 //
178
179 reg [aw-1:0] wp;
180 wire [aw-1:0] wp_pl1;
181 wire [aw-1:0] wp_pl2;
182 reg [aw-1:0] rp;
183 wire [aw-1:0] rp_pl1;
184 reg full_r;
185 reg empty_r;
186 reg gb;
187 reg gb2;
188 reg [aw:0] cnt;
189 wire full_n, empty_n;
190 reg full_n_r, empty_n_r;
191
192 ////////////////////////////////////////////////////////////////////
193 //
194 // Memory Block
195 //
196
197 generic_dpram #(aw,dw) u0(
198 .rclk( clk ),
199 .rrst( !rst ),
200 .rce( 1'b1 ),
201 .oe( 1'b1 ),
202 .raddr( rp ),
203 .do( dout ),
204 .wclk( clk ),
205 .wrst( !rst ),
206 .wce( 1'b1 ),
207 .we( we ),
208 .waddr( wp ),
209 .di( din )
210 );
211
212 ////////////////////////////////////////////////////////////////////
213 //
214 // Misc Logic
215 //
216
217 always @(posedge clk `SC_FIFO_ASYNC_RESET)
218 if(!rst) wp <= #1 {aw{1'b0}};
219 else
220 if(clr) wp <= #1 {aw{1'b0}};
221 else
222 if(we) wp <= #1 wp_pl1;
223
224 assign wp_pl1 = wp + { {aw-1{1'b0}}, 1'b1};
225 assign wp_pl2 = wp + { {aw-2{1'b0}}, 2'b10};
226
227 always @(posedge clk `SC_FIFO_ASYNC_RESET)
228 if(!rst) rp <= #1 {aw{1'b0}};
229 else
230 if(clr) rp <= #1 {aw{1'b0}};
231 else
232 if(re) rp <= #1 rp_pl1;
233
234 assign rp_pl1 = rp + { {aw-1{1'b0}}, 1'b1};
235
236 ////////////////////////////////////////////////////////////////////
237 //
238 // Combinatorial Full & Empty Flags
239 //
240
241 assign empty = ((wp == rp) & !gb);
242 assign full = ((wp == rp) & gb);
243
244 // Guard Bit ...
245 always @(posedge clk `SC_FIFO_ASYNC_RESET)
246 if(!rst) gb <= #1 1'b0;
247 else
248 if(clr) gb <= #1 1'b0;
249 else
250 if((wp_pl1 == rp) & we) gb <= #1 1'b1;
251 else
252 if(re) gb <= #1 1'b0;
253
254 ////////////////////////////////////////////////////////////////////
255 //
256 // Registered Full & Empty Flags
257 //
258
259 // Guard Bit ...
260 always @(posedge clk `SC_FIFO_ASYNC_RESET)
261 if(!rst) gb2 <= #1 1'b0;
262 else
263 if(clr) gb2 <= #1 1'b0;
264 else
265 if((wp_pl2 == rp) & we) gb2 <= #1 1'b1;
266 else
267 if((wp != rp) & re) gb2 <= #1 1'b0;
268
269 always @(posedge clk `SC_FIFO_ASYNC_RESET)
270 if(!rst) full_r <= #1 1'b0;
271 else
272 if(clr) full_r <= #1 1'b0;
273 else
274 if(we & ((wp_pl1 == rp) & gb2) & !re) full_r <= #1 1'b1;
275 else
276 if(re & ((wp_pl1 != rp) | !gb2) & !we) full_r <= #1 1'b0;
277
278 always @(posedge clk `SC_FIFO_ASYNC_RESET)
279 if(!rst) empty_r <= #1 1'b1;
280 else
281 if(clr) empty_r <= #1 1'b1;
282 else
283 if(we & ((wp != rp_pl1) | gb2) & !re) empty_r <= #1 1'b0;
284 else
285 if(re & ((wp == rp_pl1) & !gb2) & !we) empty_r <= #1 1'b1;
286
287 ////////////////////////////////////////////////////////////////////
288 //
289 // Combinatorial Full_n & Empty_n Flags
290 //
291
292 assign empty_n = cnt < n;
293 assign full_n = !(cnt < (max_size-n+1));
294 assign level = {2{cnt[aw]}} | cnt[aw-1:aw-2];
295
296 // N entries status
297 always @(posedge clk `SC_FIFO_ASYNC_RESET)
298 if(!rst) cnt <= #1 {aw+1{1'b0}};
299 else
300 if(clr) cnt <= #1 {aw+1{1'b0}};
301 else
302 if( re & !we) cnt <= #1 cnt + { {aw{1'b1}}, 1'b1};
303 else
304 if(!re & we) cnt <= #1 cnt + { {aw{1'b0}}, 1'b1};
305
306 ////////////////////////////////////////////////////////////////////
307 //
308 // Registered Full_n & Empty_n Flags
309 //
310
311 always @(posedge clk `SC_FIFO_ASYNC_RESET)
312 if(!rst) empty_n_r <= #1 1'b1;
313 else
314 if(clr) empty_n_r <= #1 1'b1;
315 else
316 if(we & (cnt >= (n-1) ) & !re) empty_n_r <= #1 1'b0;
317 else
318 if(re & (cnt <= n ) & !we) empty_n_r <= #1 1'b1;
319
320 always @(posedge clk `SC_FIFO_ASYNC_RESET)
321 if(!rst) full_n_r <= #1 1'b0;
322 else
323 if(clr) full_n_r <= #1 1'b0;
324 else
325 if(we & (cnt >= (max_size-n) ) & !re) full_n_r <= #1 1'b1;
326 else
327 if(re & (cnt <= (max_size-n+1)) & !we) full_n_r <= #1 1'b0;
328
329 ////////////////////////////////////////////////////////////////////
330 //
331 // Sanity Check
332 //
333
334 // synopsys translate_off
335 always @(posedge clk)
336 if(we & full)
337 $display("%m WARNING: Writing while fifo is FULL (%t)",$time);
338
339 always @(posedge clk)
340 if(re & empty)
341 $display("%m WARNING: Reading while fifo is EMPTY (%t)",$time);
342 // synopsys translate_on
343
344 endmodule
345
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