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[/] [System09/] [trunk/] [rtl/] [System09_Trenz_TE0141/] [secd_ram_controller_hans.vhd] - Blame information for rev 131

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1 105 davidgb
-- secd_ram_controller.vhd
2
--
3
-- Multiplex the external 16 bit SRAM to the 32 bit interface required
4
-- by the CPU and provide for an 8 bit backside port for the 6809 to
5
-- read and write SECD memory
6
 
7
library ieee;
8
 
9
use ieee.std_logic_1164.all;
10
use ieee.numeric_std.all;
11
use ieee.std_logic_unsigned.all;
12
 
13
entity secd_ram_controller is
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  port(
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    clk              : in std_logic;
16
    reset            : in std_logic;
17
 
18
    secd_stopped     : in std_logic;
19
 
20
                                        -- Internal interface to SECD (16k x 32)
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    din32            : in std_logic_vector(31 downto 0);
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    dout32           : out std_logic_vector(31 downto 0);
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    addr32           : in std_logic_vector(13 downto 0);
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    read32_enable    : in std_logic;
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    write32_enable   : in std_logic;
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    busy32           : out std_logic;
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28
                                        -- Internal interface to 6809 (64k x 8)
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    clk8             : in std_logic;
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    din8             : in std_logic_vector(7 downto 0);
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    dout8            : out std_logic_vector(7 downto 0);
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    addr8            : in std_logic_vector(15 downto 0);
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    rw8              : in std_logic;
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    cs8_ram          : in std_logic;
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    hold8            : out std_logic;
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    cs8_cf           : in std_logic;
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                                        -- External interface
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    ram_oen          : out std_logic;
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    ram_cen          : out std_logic;
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    ram_wen          : out std_logic;
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    ram_io           : inout std_logic_vector(15 downto 0);
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    ram_a            : out std_logic_vector(20 downto 1);
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    ram_bhen         : out std_logic;
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    ram_blen         : out std_logic
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    );
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end;
48
 
49
architecture external_ram of secd_ram_controller is
50
 
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  type hold_state_type is ( hold_release_state, hold_request_state );
52
 
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  signal cf_hold_state : hold_state_type;
54
 
55
  signal cf_release  : std_logic;
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  signal cf_count    : std_logic_vector(3 downto 0);
57
 
58
  type state_type is (idle,
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                      read32_high, read32_high_deselect, read32_low,
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                      write32_high, write32_high_deselect, write32_low,
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                      read8_ram, write8_ram, read8_cf, write8_cf );
62
 
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  signal state : state_type;
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  signal dout8_en : std_logic;
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66
begin
67
 
68
 
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  secd_ram_process : process( clk, state, reset,
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                              read32_enable, write32_enable, addr32, din32,
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                              cs8_ram, rw8, addr8, din8 )
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  begin
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    if reset = '1' then
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        ram_a(20 downto 1) <= (others => '0');
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        ram_cen  <= '1';
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        ram_oen  <= '1';
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        ram_wen  <= '1';
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        ram_bhen <= '1';
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        ram_blen <= '1';
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        ram_io   <= (others => 'Z');
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                  dout8_en <= '0';
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        hold8    <= '0';
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        busy32   <= '0';
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        state    <= idle;
85
    elsif rising_edge(clk) then
86
      case state is
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        when idle =>
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          ram_a(20 downto 1) <= (others => '0');
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          ram_cen  <= '1';
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          ram_oen  <= '1';
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          ram_wen  <= '1';
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          ram_bhen <= '1';
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          ram_blen <= '1';
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          ram_io   <= (others => 'Z');
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          dout8_en <= '0';
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          if read32_enable = '1' then
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            ram_a(1) <= '0';
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            ram_a(20 downto 2) <= "00000" & addr32(13 downto 0);
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            ram_cen  <= '0';
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            ram_oen  <= '0';
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            ram_wen  <= '1';
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            ram_bhen <= '0';
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            ram_blen <= '0';
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            hold8    <= cs8_ram or cs8_cf;
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            busy32   <= '1';
106
            state    <= read32_high;
107
          elsif write32_enable = '1' then
108
            ram_a(1) <= '0';
109
            ram_a(20 downto 2) <= "00000" & addr32(13 downto 0);
110
            ram_cen  <= '0';
111
            ram_oen  <= '1';
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            ram_wen  <= '0';
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            ram_bhen <= '0';
114
            ram_blen <= '0';
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            ram_io   <= din32(31 downto 16);
116
            hold8    <= cs8_ram or cs8_cf;
117
            busy32   <= '1';
118
            state <= write32_high;
119
          elsif (cs8_ram = '1') and (rw8 = '1') then
120
            ram_a(20 downto 1) <= "00000" & addr8(15 downto 1);
121
            ram_cen  <= '0';
122
            ram_oen  <= '0';
123
            ram_wen  <= '1';
124
            ram_bhen <= addr8(0);
125
            ram_blen <= not addr8(0);
126
            dout8_en <= '1';
127
            hold8    <= '0';
128
            busy32   <= '1';
129
            state    <= read8_ram;
130
          elsif (cs8_ram = '1') and (rw8 = '0') then
131
            ram_a(20 downto 1) <= "00000" & addr8(15 downto 1);
132
            ram_cen  <= '0';
133
            ram_oen  <= '1';
134
            ram_wen  <= '0';
135
            ram_bhen <= addr8(0);
136
            ram_blen <= not addr8(0);
137
            if addr8(0) = '0' then
138
              ram_io(15 downto 8) <= din8;
139
              ram_io( 7 downto 0) <= (others => 'Z');
140
            else
141
              ram_io(15 downto 8) <= (others => 'Z');
142
              ram_io( 7 downto 0) <= din8;
143
            end if;
144
            hold8    <= '0';
145
            busy32   <= '1';
146
            state    <= write8_ram;
147
          elsif (cs8_cf = '1') and (rw8 = '1') then
148
            ram_a(20 downto 1) <= "00000" & addr8(15 downto 1);
149
            dout8_en <= '1';
150
            busy32   <= '1';
151
            if cf_release = '1' then
152
              hold8  <= '0';
153
              state  <= read8_cf;
154
            else
155
              hold8  <= '1';
156
              state  <= idle;
157
            end if;
158
          elsif (cs8_cf = '1') and (rw8 = '0') then
159
            ram_a(20 downto 1) <= "00000" & addr8(15 downto 1);
160
            busy32   <= '1';
161
            if addr8(0) = '0' then
162
              ram_io(15 downto 8) <= din8;
163
              ram_io( 7 downto 0) <= (others => 'Z');
164
            else
165
              ram_io(15 downto 8) <= (others => 'Z');
166
              ram_io( 7 downto 0) <= din8;
167
            end if;
168
            if cf_release = '1' then
169
              hold8  <= '0';
170
              state  <= write8_cf;
171
            else
172
              hold8  <= '1';
173
              state  <= idle;
174
            end if;
175
          else
176
            hold8    <= '0';
177
            busy32   <= '0';
178
            state    <= idle;
179
          end if;
180
 
181
        when read32_high =>
182
          ram_a(1) <= '1';
183
          ram_a(20 downto 2) <= "00000" & addr32(13 downto 0);
184
          ram_cen  <= '1';
185
          ram_oen  <= '1';
186
          ram_wen  <= '1';
187
          ram_bhen <= '1';
188
          ram_blen <= '1';
189
          ram_io   <= (others => 'Z');
190
                         dout32(31 downto 16) <= ram_io;
191
          busy32   <= '1';
192
          dout8_en <= '0';
193
          hold8    <= cs8_ram or cs8_cf;
194
          state    <= read32_high_deselect;
195
 
196
        when read32_high_deselect =>
197
          ram_a(1) <= '1';
198
          ram_a(20 downto 2) <= "00000" & addr32(13 downto 0);
199
          ram_cen  <= '0';
200
          ram_oen  <= '0';
201
          ram_wen  <= '1';
202
          ram_bhen <= '0';
203
          ram_blen <= '0';
204
          ram_io   <= (others => 'Z');
205
          busy32   <= '1';
206
          dout8_en <= '0';
207
          hold8    <= cs8_ram or cs8_cf;
208
          state    <= read32_low;
209
 
210
        when read32_low =>
211
          ram_a(1) <= '0';
212
          ram_a(20 downto 2) <= "00000" & addr32(13 downto 0);
213
          ram_cen  <= '1';
214
          ram_oen  <= '1';
215
          ram_wen  <= '1';
216
          ram_bhen <= '1';
217
          ram_blen <= '1';
218
          ram_io   <= (others => 'Z');
219
                         dout32(15 downto 0) <= ram_io;
220
          busy32   <= '0';
221
          dout8_en <= '0';
222
          hold8    <= cs8_ram or cs8_cf;
223
          state    <= idle;
224
 
225
        when write32_high =>
226
          ram_a(1) <= '1';
227
          ram_a(20 downto 2) <= "00000" & addr32(13 downto 0);
228
          ram_cen  <= '1';
229
          ram_oen  <= '1';
230
          ram_wen  <= '1';
231
          ram_bhen <= '1';
232
          ram_blen <= '1';
233
          ram_io   <= (others => 'Z');
234
          busy32   <= '1';
235
          dout8_en <= '0';
236
          hold8    <= cs8_ram or cs8_cf;
237
          state    <= write32_high_deselect;
238
 
239
        when write32_high_deselect =>
240
          ram_a(1) <= '1';
241
          ram_a(20 downto 2) <= "00000" & addr32(13 downto 0);
242
          ram_cen  <= '0';
243
          ram_oen  <= '1';
244
          ram_wen  <= '0';
245
          ram_bhen <= '0';
246
          ram_blen <= '0';
247
          ram_io   <= din32(15 downto 0);
248
          busy32   <= '1';
249
          dout8_en <= '0';
250
          hold8    <= cs8_ram or cs8_cf;
251
          state    <= write32_low;
252
 
253
        when write32_low =>
254
          ram_a(1) <= '0';
255
          ram_a(20 downto 2) <= "00000" & addr32(13 downto 0);
256
          ram_cen  <= '1';
257
          ram_oen  <= '1';
258
          ram_wen  <= '1';
259
          ram_bhen <= '1';
260
          ram_blen <= '1';
261
          ram_io   <= (others => 'Z');
262
          busy32   <= '0';
263
          dout8_en <= '0';
264
          hold8    <= cs8_ram or cs8_cf;
265
          state    <= idle;
266
 
267
        when read8_ram =>
268
          ram_a(20 downto 1) <= "00000" & addr8(15 downto 1);
269
          ram_cen  <= '1';
270
          ram_oen  <= '1';
271
          ram_wen  <= '1';
272
          ram_io   <= (others => 'Z');
273
          busy32   <= '0';
274
          dout8_en <= '0';
275
          hold8    <= '0';
276
          state    <= idle;
277
 
278
        when write8_ram =>
279
          ram_a(20 downto 1) <= "00000" & addr8(15 downto 1);
280
          ram_cen  <= '1';
281
          ram_oen  <= '1';
282
          ram_wen  <= '1';
283
          ram_io(15 downto 0) <= (others => 'Z');
284
          busy32   <= '0';
285
          dout8_en <= '0';
286
          hold8    <= '0';
287
          state    <= idle;
288
 
289
        when read8_cf =>
290
          ram_a(20 downto 1) <= "00000" & addr8(15 downto 1);
291
          ram_cen  <= '1';
292
          ram_oen  <= '1';
293
          ram_wen  <= '1';
294
          ram_bhen <= '1';
295
          ram_blen <= '1';
296
          ram_io   <= (others => 'Z');
297
          busy32   <= '0';
298
          dout8_en <= '0';
299
          hold8    <= '0';
300
          state    <= idle;
301
 
302
        when write8_cf =>
303
          ram_a(1) <= '1';
304
          ram_a(20 downto 1) <= "00000" & addr8(15 downto 1);
305
          ram_cen  <= '1';
306
          ram_oen  <= '1';
307
          ram_wen  <= '1';
308
          ram_bhen <= '1';
309
          ram_blen <= '1';
310
          busy32   <= '1';
311
          dout8_en <= '0';
312
          hold8    <= '0';
313
          state    <= idle;
314
 
315
        when others =>
316
          null;
317
 
318
      end case;
319
    end if;
320
  end process;
321
 
322
--
323
-- 8 Bit data bus output enable process
324
--
325
-- The point of this process is that data must be
326
-- passed through from the ram input,
327
-- and not clocked, so it is ready for the CPU
328
-- on the trailing clock edge
329
--  
330
dout8_selector : process( dout8_en, addr8, ram_io )
331
begin
332
    if dout8_en = '0' then
333
             dout8 <= ( others => '0' );
334
    else
335
        if addr8(0) = '0' then
336
            dout8 <= ram_io(15 downto 8);
337
        else
338
            dout8 <= ram_io(7 downto 0);
339
        end if;
340
    end if;
341
end process;
342
 
343
--
344
-- Hold CF access       for a few cycles
345
-- synchronize with the CPU clock
346
-- hold release is set on the rising edge
347
-- of the CPU clock so that you have one
348
-- VGA clock cycle to return to the idle state
349
-- of the secd_ram_process state machine.
350
--
351
  cf_hold_proc: process( clk8, reset )
352
  begin
353
    if reset = '1' then
354
      cf_release    <= '0';
355
      cf_count      <= "0000";
356
      cf_hold_state <= hold_release_state;
357
    elsif rising_edge( clk8 ) then
358
      case cf_hold_state is
359
        when hold_release_state =>
360
          cf_release <= '0';
361
          if cs8_cf = '1' then
362
            cf_count      <= "0011";
363
            cf_hold_state <= hold_request_state;
364
          end if;
365
 
366
        when hold_request_state =>
367
          cf_count <= cf_count - "0001";
368
          if cf_count = "0000" then
369
            cf_release    <= '1';
370
            cf_hold_state <= hold_release_state;
371
          end if;
372
        when others =>
373
          null;
374
      end case;
375
    end if;
376
 
377
  end process;
378
 
379
end;

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