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[/] [light8080/] [trunk/] [vhdl/] [light8080.vhdl] - Blame information for rev 53

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Line No. Rev Author Line
1 2 ja_rd
--##############################################################################
2 10 ja_rd
-- light8080 : Intel 8080 binary compatible core
3 2 ja_rd
--##############################################################################
4 10 ja_rd
-- v1.1    (20 sep 2008) Microcode bug in INR fixed.
5
-- v1.0    (05 nov 2007) First release. Jose A. Ruiz.
6
--
7 19 ja_rd
-- This file and all the light8080 project files are freeware (See COPYING.TXT)
8 3 ja_rd
--##############################################################################
9 19 ja_rd
-- (See timing diagrams at bottom of file. More comprehensive explainations can 
10
-- be found in the design notes)
11 10 ja_rd
--##############################################################################
12 2 ja_rd
 
13
library IEEE;
14
use IEEE.STD_LOGIC_1164.ALL;
15
use IEEE.STD_LOGIC_ARITH.ALL;
16
use IEEE.STD_LOGIC_UNSIGNED.ALL;
17
 
18
--##############################################################################
19
-- vma :      enable a memory or io r/w access.
20
-- io :       access in progress is io (and not memory) 
21
-- rd :       read memory or io 
22
-- wr :       write memory or io
23
-- data_out : data output
24
-- addr_out : memory and io address
25
-- data_in :  data input
26
-- halt :     halt status (1 when in halt state)
27
-- inte :     interrupt status (1 when enabled)
28
-- intr :     interrupt request
29
-- inta :     interrupt acknowledge
30
-- reset :    synchronous reset
31
-- clk :      clock
32 19 ja_rd
--
33
-- (see timing diagrams at bottom of file)
34 2 ja_rd
--##############################################################################
35
entity light8080 is
36
    Port (
37
            addr_out :  out std_logic_vector(15 downto 0);
38
 
39
            inta :      out std_logic;
40
            inte :      out std_logic;
41
            halt :      out std_logic;
42
            intr :      in std_logic;
43
 
44
            vma :       out std_logic;
45
            io :        out std_logic;
46
            rd :        out std_logic;
47
            wr :        out std_logic;
48 19 ja_rd
            fetch :     out std_logic;
49 2 ja_rd
            data_in :   in std_logic_vector(7 downto 0);
50
            data_out :  out std_logic_vector(7 downto 0);
51
 
52
            clk :       in std_logic;
53
            reset :     in std_logic );
54
end light8080;
55
 
56
--##############################################################################
57 10 ja_rd
-- All memory and io accesses are synchronous (rising clock edge). Signal vma 
58
-- works as the master memory and io synchronous enable. More specifically:
59 2 ja_rd
--
60
--    * All memory/io control signals (io,rd,wr) are valid only when vma is 
61
--      high. They never activate when vms is inactive. 
62
--    * Signals data_out and address are only valid when vma='1'. The high 
63 10 ja_rd
--      address byte is 0x00 for all io accesses.
64
--    * Signal data_in should be valid by the end of the cycle after vma='1', 
65
--      data is clocked in by the rising clock edge.
66 2 ja_rd
--
67 10 ja_rd
-- All signals are assumed to be synchronous to the master clock. Prevention of
68
-- metastability, if necessary, is up to you.
69
-- 
70
-- Signal reset needs to be active for just 1 clock cycle (it is sampled on a 
71
-- positive clock edge and is subject to setup and hold times).
72 4 ja_rd
-- Once reset is deasserted, the first fetch at address 0x0000 will happen 4
73 2 ja_rd
-- cycles later.
74
--
75
-- Signal intr is sampled on all positive clock edges. If asserted when inte is
76 4 ja_rd
-- high, interrupts will be disabled, inta will be asserted high and a fetch 
77 39 ja_rd
-- cycle will occur immediately after the current instruction ends execution,
78
-- except if intr was asserted at the last cycle of an instruction. In that case
79
-- it will be honored after the next instruction ends.
80
-- The fetched instruction will be executed normally, except that PC will not 
81
-- be valid in any subsequent fetch cycles of the same instruction, 
82 10 ja_rd
-- and will not be incremented (In practice, the same as the original 8080).
83 39 ja_rd
-- inta will remain high for the duration of the fetched instruction, including
84
-- fetch and execution time (in the original 8080 it was high only for the 
85
-- opcode fetch cycle). 
86 10 ja_rd
-- PC will not be autoincremented while inta is high, but it can be explicitly 
87 39 ja_rd
-- modified (e.g. RST, CALL, etc.). Again, the same as the original.
88 2 ja_rd
-- Interrupts will be disabled upon assertion of inta, and remain disabled 
89 4 ja_rd
-- until explicitly enabled by the program (as in the original).
90 39 ja_rd
-- If intr is asserted when inte is low, the interrupt will not be attended but
91
-- it will be registered in an int_pending flag, so it will be honored when 
92
-- interrupts are enabled.
93
-- 
94 2 ja_rd
--
95 4 ja_rd
-- The above means that any instruction can be supplied in an inta cycle, 
96 10 ja_rd
-- either single byte or multibyte. See the design notes.
97 2 ja_rd
--##############################################################################
98
 
99
architecture microcoded of light8080 is
100
 
101
-- addr_low: low byte of address
102
signal addr_low :     std_logic_vector(7 downto 0);
103
-- IR: instruction register. some bits left unused.  
104
signal IR :           std_logic_vector(7 downto 0);
105
-- s_field: IR field, sss source reg code
106
signal s_field :      std_logic_vector(2 downto 0);
107
-- d_field: IR field, ddd destination reg code
108
signal d_field :      std_logic_vector(2 downto 0);
109
-- p_field: IR field, pp 16-bit reg pair code
110
signal p_field :      std_logic_vector(1 downto 0);
111
-- rbh: 1 when p_field=11, used in reg bank addressing for 'special' regs
112
signal rbh :          std_logic; -- 1 when P=11 (special case)  
113
-- alu_op: uinst field, ALU operation code 
114
signal alu_op :       std_logic_vector(3 downto 0);
115
-- DI: data input to ALU block from data_in, unregistered
116
signal DI :           std_logic_vector(7 downto 0);
117
-- uc_addr: microcode (ucode) address 
118
signal uc_addr :      std_logic_vector(7 downto 0);
119
-- next_uc_addr: computed next microcode address (uaddr++/jump/ret/fetch)
120
signal next_uc_addr : std_logic_vector(8 downto 0);
121
-- uc_jmp_addr: uinst field, absolute ucode jump address
122
signal uc_jmp_addr :  std_logic_vector(7 downto 0);
123
-- uc_ret_address: ucode return address saved in previous jump
124
signal uc_ret_addr :  std_logic_vector(7 downto 0);
125
-- addr_plus_1: uaddr + 1
126
signal addr_plus_1 :  std_logic_vector(7 downto 0);
127
-- do_reset: reset, delayed 1 cycle -- used to reset the microcode sequencer
128
signal do_reset :     std_logic;
129
 
130
-- uc_flags1: uinst field, encoded flag of group 1 (see ucode file)
131
signal uc_flags1 :    std_logic_vector(2 downto 0);
132
-- uc_flags2: uinst field, encoded flag of group 2 (see ucode file)
133
signal uc_flags2 :    std_logic_vector(2 downto 0);
134
-- uc_addr_sel: selection of next uc_addr, composition of 4 flags
135
signal uc_addr_sel :  std_logic_vector(3 downto 0);
136
-- NOTE: see microcode file for information on flags
137
signal uc_jsr :       std_logic;  -- uinst field, decoded 'jsr' flag
138
signal uc_tjsr :      std_logic;  -- uinst field, decoded 'tjsr' flag
139
signal uc_decode :    std_logic;  -- uinst field, decoded 'decode' flag
140
signal uc_end :       std_logic;  -- uinst field, decoded 'end' flag
141
signal condition_reg :std_logic;  -- registered tjst condition
142
-- condition: tjsr condition (computed ccc condition from '80 instructions)
143
signal condition :    std_logic;
144
-- condition_sel: IR field, ccc condition code
145
signal condition_sel :std_logic_vector(2 downto 0);
146
signal uc_do_jmp :    std_logic;  -- uinst jump (jsr/tjsr) flag, pipelined
147
signal uc_do_ret :    std_logic;  -- ret flag, pipelined
148
signal uc_halt_flag : std_logic;  -- uinst field, decoded 'halt' flag
149
signal uc_halt :      std_logic;  -- halt command
150
signal halt_reg :     std_logic;  -- halt status reg, output as 'halt' signal
151
signal uc_ei :        std_logic;  -- uinst field, decoded 'ei' flag
152 49 ja_rd
signal uc_di :        std_logic;  -- uinst field, decoded 'di' flag
153 2 ja_rd
signal inte_reg :     std_logic;  -- inte status reg, output as 'inte' signal
154
signal int_pending :  std_logic;  -- intr requested, inta not active yet
155
signal inta_reg :     std_logic;  -- inta status reg, output as 'inta'
156
signal clr_t1 :       std_logic;  -- uinst field, explicitly erase T1
157
signal do_clr_t1 :    std_logic;  -- clr_t1 pipelined
158
signal clr_t2 :       std_logic;  -- uinst field, explicitly erase T2
159
signal do_clr_t2 :    std_logic;  -- clr_t2 pipelined
160
signal ucode :        std_logic_vector(31 downto 0); -- microcode word
161
signal ucode_field2 : std_logic_vector(24 downto 0); -- pipelined microcode
162
 
163 49 ja_rd
-- used to delay interrup enable for one entire instruction after EI
164
signal delayed_ei :   std_logic;
165
 
166 2 ja_rd
-- microcode ROM : see design notes and microcode source file 
167
type t_rom is array (0 to 511) of std_logic_vector(31 downto 0);
168
 
169
signal rom : t_rom := (
170
"00000000000000000000000000000000", -- 000
171
"00000000000001001000000001000100", -- 001
172
"00000000000001000000000001000100", -- 002
173
"10111101101001001000000001001101", -- 003
174
"10110110101001000000000001001101", -- 004
175
"00100000000000000000000000000000", -- 005
176
"00000000000000000000000000000000", -- 006
177
"11100100000000000000000000000000", -- 007
178
"00000000101010000000000000000000", -- 008
179
"00000100000100000000000001010111", -- 009
180
"00001000000000000000110000011001", -- 00a
181
"00000100000100000000000001010111", -- 00b
182
"00000000101010000000000010010111", -- 00c
183
"00001000000000000000110000011100", -- 00d
184
"00001000000000000000110000011111", -- 00e
185
"00000100000100000000000001010111", -- 00f
186
"00001000000000000000110000011111", -- 010
187
"00001000000000000000110000011100", -- 011
188
"00001000000000000000110000011111", -- 012
189
"00000000000110001000000001010111", -- 013
190
"00001000000000000000110000011111", -- 014
191
"00000100000110000000000001010111", -- 015
192
"00001000000000000000110000101110", -- 016
193
"00001000000000000000110000100010", -- 017
194
"00000100000000111000000001010111", -- 018
195
"00001000000000000000110000101110", -- 019
196
"00000000101000111000000010010111", -- 01a
197
"00001000000000000000110000100101", -- 01b
198
"00001000000000000000110000101110", -- 01c
199
"10111101101001100000000001001101", -- 01d
200
"10110110101001101000000001001101", -- 01e
201
"00000000100000101000000001010111", -- 01f
202
"00001000000000000000110000100010", -- 020
203
"00000100000000100000000001010111", -- 021
204
"00001000000000000000110000101110", -- 022
205
"00000000101000101000000010010111", -- 023
206
"10111101101001100000000001001101", -- 024
207
"10111010101001101000000001001101", -- 025
208
"00000000101000100000000010010111", -- 026
209
"00001000000000000000110000100101", -- 027
210
"00001000000000000000110000101000", -- 028
211
"00000100000000111000000001010111", -- 029
212
"00000000101000111000000010010111", -- 02a
213
"00001000000000000000110000101011", -- 02b
214
"00000000101000010000000000000000", -- 02c
215
"00000000000001010000000001010111", -- 02d
216
"00000000101000011000000000000000", -- 02e
217
"00000000000001011000000001010111", -- 02f
218
"00000000101000100000000000000000", -- 030
219
"00000000000000010000000001010111", -- 031
220
"00000000101000101000000000000000", -- 032
221
"00000000000000011000000001010111", -- 033
222
"00000000101001010000000000000000", -- 034
223
"00000000000000100000000001010111", -- 035
224
"00000000101001011000000000000000", -- 036
225
"00000100000000101000000001010111", -- 037
226
"00001000000000000000110000011111", -- 038
227
"00000100011000111000001101001100", -- 039
228
"00001000000000000000110000011111", -- 03a
229
"00000100011000111000001101001101", -- 03b
230
"00001000000000000000110000011111", -- 03c
231
"00000100011000111000001101001110", -- 03d
232
"00001000000000000000110000011111", -- 03e
233
"00000100011000111000001101001111", -- 03f
234
"00001000000000000000110000011111", -- 040
235
"00000100011000111000001101000100", -- 041
236
"00001000000000000000110000011111", -- 042
237
"00000100011000111000001101000101", -- 043
238
"00001000000000000000110000011111", -- 044
239
"00000100011000111000001101000110", -- 045
240
"00001000000000000000110000011111", -- 046
241
"00000100011000111000001110001110", -- 047
242
"00000000101010000000000000000000", -- 048
243
"00000100011000111000001101001100", -- 049
244
"00000000101010000000000000000000", -- 04a
245
"00000100011000111000001101001101", -- 04b
246
"00000000101010000000000000000000", -- 04c
247
"00000100011000111000001101001110", -- 04d
248
"00000000101010000000000000000000", -- 04e
249
"00000100011000111000001101001111", -- 04f
250
"00000000101010000000000000000000", -- 050
251
"00000100011000111000001101000100", -- 051
252
"00000000101010000000000000000000", -- 052
253
"00000100011000111000001101000101", -- 053
254
"00000000101010000000000000000000", -- 054
255
"00000100011000111000001101000110", -- 055
256
"00000000101010000000000000000000", -- 056
257
"00000100011000111000001110001110", -- 057
258
"00001000000000000000110000011001", -- 058
259
"00000100011000111000001101001100", -- 059
260
"00001000000000000000110000011001", -- 05a
261
"00000100011000111000001101001101", -- 05b
262
"00001000000000000000110000011001", -- 05c
263
"00000100011000111000001101001110", -- 05d
264
"00001000000000000000110000011001", -- 05e
265
"00000100011000111000001101001111", -- 05f
266
"00001000000000000000110000011001", -- 060
267
"00000100011000111000001101000100", -- 061
268
"00001000000000000000110000011001", -- 062
269
"00000100011000111000001101000101", -- 063
270
"00001000000000000000110000011001", -- 064
271
"00000100011000111000001101000110", -- 065
272
"00001000000000000000110000011001", -- 066
273
"00000100011000111000001110001110", -- 067
274
"10111100101100000000001001001101", -- 068
275
"00000100000000000000000000000000", -- 069
276
"00001000000000000000110000011001", -- 06a
277 6 ja_rd
"10111100000000000000001010001101", -- 06b
278 2 ja_rd
"00001000000000000000110000011100", -- 06c
279
"10111100011100000000001001001111", -- 06d
280
"00000100000000000000000000000000", -- 06e
281
"00001000000000000000110000011001", -- 06f
282
"11000000000000000000000000000000", -- 070
283
"10111100011001010000001010001111", -- 071
284
"00001000000000000000110000011100", -- 072
285
"10111100101110001000000001001101", -- 073
286
"10100100101110000000000001001101", -- 074
287
"10111100011110001000000001001111", -- 075
288
"10100100011110000000000001001111", -- 076
289
"00000000011110001000000000000000", -- 077
290
"00000000101000101000000101001100", -- 078
291
"00000000011110000000000000000000", -- 079
292
"00000100101000100000000101001101", -- 07a
293
"00000000101000111000000010101000", -- 07b
294
"00000100101000111000001101101000", -- 07c
295
"00000100101000111000000101000000", -- 07d
296
"00000100101000111000000101000001", -- 07e
297
"00000100101000111000000101000010", -- 07f
298
"00000100101000111000000101000011", -- 080
299
"00000100101000111000000001000111", -- 081
300
"00000100000000000000000100101100", -- 082
301
"00000100000000000000000100101101", -- 083
302
"00001000000000000000110000101110", -- 084
303
"00000000101001100000000000000000", -- 085
304
"00000000000001001000000001010111", -- 086
305
"00000000101001101000000000000000", -- 087
306
"00000100000001000000000001010111", -- 088
307
"00000100000000000000000000000000", -- 089
308
"00001000000000000000110000101110", -- 08a
309
"00010000000000000000100000000101", -- 08b
310
"00001000000000000000110000101110", -- 08c
311
"11000000101001000000000010010111", -- 08d
312
"00001000000000000000110000110100", -- 08e
313
"11000000101001001000000010010111", -- 08f
314
"00001000000000000000110000110100", -- 090
315
"00000000101001100000000000000000", -- 091
316
"00000000000001001000000001010111", -- 092
317
"00000000101001101000000000000000", -- 093
318
"00000100000001000000000001010111", -- 094
319
"00001000000000000000110000101110", -- 095
320
"00010000000000000000100000001101", -- 096
321
"00001000000000000000110000111001", -- 097
322
"00000000000001001000000001010111", -- 098
323
"00001000000000000000110000111001", -- 099
324
"00000100000001000000000001010111", -- 09a
325
"00010000000000000000100000010111", -- 09b
326
"11000000101001000000000010010111", -- 09c
327
"00001000000000000000110000110100", -- 09d
328
"11000000101001001000000010010111", -- 09e
329
"00001000000000000000110000110100", -- 09f
330
"11000000000001001000000001011111", -- 0a0
331
"00000100000001000000000001000100", -- 0a1
332
"00000000101000101000000000000000", -- 0a2
333
"00000000000001001000000001010111", -- 0a3
334
"00000000101000100000000000000000", -- 0a4
335
"00000100000001000000000001010111", -- 0a5
336
"11000000101110000000000010010111", -- 0a6
337
"00001000000000000000110000110100", -- 0a7
338
"11000000101110001000000010010111", -- 0a8
339
"00001000000000000000110000110100", -- 0a9
340
"00000100000000000000000000000000", -- 0aa
341
"11000000101000111000000010010111", -- 0ab
342
"00001000000000000000110000110100", -- 0ac
343
"11000000000000000000000010110000", -- 0ad
344
"00001000000000000000110000110100", -- 0ae
345
"00000100000000000000000000000000", -- 0af
346
"00001000000000000000110000111001", -- 0b0
347
"00000000000110001000000001010111", -- 0b1
348
"00001000000000000000110000111001", -- 0b2
349
"00000100000110000000000001010111", -- 0b3
350
"00001000000000000000110000111001", -- 0b4
351
"00000000000000110000001101010111", -- 0b5
352
"00001000000000000000110000111001", -- 0b6
353
"00000100000000111000000001010111", -- 0b7
354
"00001000000000000000110000111001", -- 0b8
355
"00000000000001100000000001010111", -- 0b9
356
"00001000000000000000110000111001", -- 0ba
357
"00000000000001101000000001010111", -- 0bb
358
"11000000101000100000000010010111", -- 0bc
359
"00001000000000000000110000110100", -- 0bd
360
"11000000101000101000000010010111", -- 0be
361
"00001000000000000000110000110100", -- 0bf
362
"00000000101001100000000000000000", -- 0c0
363
"00000000000000101000000001010111", -- 0c1
364
"00000000101001101000000000000000", -- 0c2
365
"00000100000000100000000001010111", -- 0c3
366
"00000000101000101000000000000000", -- 0c4
367
"00000000000001111000000001010111", -- 0c5
368
"00000000101000100000000000000000", -- 0c6
369
"00000100000001110000000001010111", -- 0c7
370
"01100100000000000000000000000000", -- 0c8
371
"01000100000000000000000000000000", -- 0c9
372
"00000000000001101000000001010111", -- 0ca
373
"00001000000000000000110000011111", -- 0cb
374
"00000000000001100000000001010111", -- 0cc
375
"00000000000000000000000000000000", -- 0cd
376
"00000001101001100000000000000000", -- 0ce
377
"10010110101001101000000000000000", -- 0cf
378
"00000100100000111000000001010111", -- 0d0
379
"00000000000001101000000001010111", -- 0d1
380
"00001000000000000000110000011111", -- 0d2
381
"00000000000001100000000001010111", -- 0d3
382
"00000000101000111000000010010111", -- 0d4
383
"00000001101001100000000000000000", -- 0d5
384
"10011010101001101000000000000000", -- 0d6
385
"00000100000000000000000000000000", -- 0d7
386
"11100100000000000000000000000000", -- 0d8
387
"00000001101000101000000000000000", -- 0d9
388
"00010110101000100000000000000000", -- 0da
389
"00001100100001010000000001010111", -- 0db
390
"00000001101000101000000000000000", -- 0dc
391
"00011010101000100000000000000000", -- 0dd
392
"00000100000000000000000000000000", -- 0de
393
"10111101101001001000000001001101", -- 0df
394
"10110110101001000000000001001101", -- 0e0
395
"00001100100000000000000010010111", -- 0e1
396
"00000001101001100000000000000000", -- 0e2
397
"00010110101001101000000000000000", -- 0e3
398
"00001100100000000000000000000000", -- 0e4
399
"00000001101001100000000000000000", -- 0e5
400
"00011010101001101000000000000000", -- 0e6
401
"00000100000000000000000000000000", -- 0e7
402
"00000001101110001000000000000000", -- 0e8
403
"00010110101110000000000000000000", -- 0e9
404
"00001100100000000000000000000000", -- 0ea
405
"00000001101110001000000000000000", -- 0eb
406
"00011010101110000000000000000000", -- 0ec
407
"00000100000000000000000000000000", -- 0ed
408
"10111101101001001000000001001101", -- 0ee
409
"10110110101001000000000001001101", -- 0ef
410
"00000000100001100000000001010111", -- 0f0
411
"10111101101001001000000001001101", -- 0f1
412
"10110110101001000000000001001101", -- 0f2
413
"00001100100001101000000001010111", -- 0f3
414
"10111100011001111000000001001111", -- 0f4
415
"10100000011001110000000001001111", -- 0f5
416
"00000001101001111000000000000000", -- 0f6
417
"00011010101001110000000000000000", -- 0f7
418
"00001100000000000000000000000000", -- 0f8
419
"10111101101001111000000001001101", -- 0f9
420
"10110110101001110000000001001101", -- 0fa
421
"00001100100000000000000000000000", -- 0fb
422
"00000100000000000000000000000000", -- 0fc
423
"00000100000000000000000000000000", -- 0fd
424
"00000100000000000000000000000000", -- 0fe
425
"00000100000000000000000000000000", -- 0ff
426
"00001000000000000000100000001001", -- 100
427
"00001000000000000000000000010010", -- 101
428
"00001000000000000000000000101010", -- 102
429
"00001000000000000000010000110011", -- 103
430
"00001000000000000000010000101000", -- 104
431
"00001000000000000000010000101101", -- 105
432
"00001000000000000000000000001110", -- 106
433
"00001000000000000000010000111101", -- 107
434
"00001000000000000000000000000000", -- 108
435
"00001000000000000000010000110111", -- 109
436
"00001000000000000000000000101000", -- 10a
437
"00001000000000000000010000110101", -- 10b
438
"00001000000000000000010000101000", -- 10c
439
"00001000000000000000010000101101", -- 10d
440
"00001000000000000000000000001110", -- 10e
441
"00001000000000000000010000111110", -- 10f
442
"00001000000000000000000000000000", -- 110
443
"00001000000000000000000000010010", -- 111
444
"00001000000000000000000000101010", -- 112
445
"00001000000000000000010000110011", -- 113
446
"00001000000000000000010000101000", -- 114
447
"00001000000000000000010000101101", -- 115
448
"00001000000000000000000000001110", -- 116
449
"00001000000000000000010000111111", -- 117
450
"00001000000000000000000000000000", -- 118
451
"00001000000000000000010000110111", -- 119
452
"00001000000000000000000000101000", -- 11a
453
"00001000000000000000010000110101", -- 11b
454
"00001000000000000000010000101000", -- 11c
455
"00001000000000000000010000101101", -- 11d
456
"00001000000000000000000000001110", -- 11e
457
"00001000000000000000100000000000", -- 11f
458
"00001000000000000000000000000000", -- 120
459
"00001000000000000000000000010010", -- 121
460
"00001000000000000000000000100010", -- 122
461
"00001000000000000000010000110011", -- 123
462
"00001000000000000000010000101000", -- 124
463
"00001000000000000000010000101101", -- 125
464
"00001000000000000000000000001110", -- 126
465
"00001000000000000000010000111011", -- 127
466
"00001000000000000000000000000000", -- 128
467
"00001000000000000000010000110111", -- 129
468
"00001000000000000000000000011100", -- 12a
469
"00001000000000000000010000110101", -- 12b
470
"00001000000000000000010000101000", -- 12c
471
"00001000000000000000010000101101", -- 12d
472
"00001000000000000000000000001110", -- 12e
473
"00001000000000000000100000000001", -- 12f
474
"00001000000000000000000000000000", -- 130
475
"00001000000000000000000000010010", -- 131
476
"00001000000000000000000000011001", -- 132
477
"00001000000000000000010000110011", -- 133
478
"00001000000000000000010000101010", -- 134
479
"00001000000000000000010000101111", -- 135
480
"00001000000000000000000000010000", -- 136
481
"00001000000000000000100000000011", -- 137
482
"00001000000000000000000000000000", -- 138
483
"00001000000000000000010000110111", -- 139
484
"00001000000000000000000000010110", -- 13a
485
"00001000000000000000010000110101", -- 13b
486
"00001000000000000000010000101000", -- 13c
487
"00001000000000000000010000101101", -- 13d
488
"00001000000000000000000000001110", -- 13e
489
"00001000000000000000100000000010", -- 13f
490
"00001000000000000000000000001000", -- 140
491
"00001000000000000000000000001000", -- 141
492
"00001000000000000000000000001000", -- 142
493
"00001000000000000000000000001000", -- 143
494
"00001000000000000000000000001000", -- 144
495
"00001000000000000000000000001000", -- 145
496
"00001000000000000000000000001010", -- 146
497
"00001000000000000000000000001000", -- 147
498
"00001000000000000000000000001000", -- 148
499
"00001000000000000000000000001000", -- 149
500
"00001000000000000000000000001000", -- 14a
501
"00001000000000000000000000001000", -- 14b
502
"00001000000000000000000000001000", -- 14c
503
"00001000000000000000000000001000", -- 14d
504
"00001000000000000000000000001010", -- 14e
505
"00001000000000000000000000001000", -- 14f
506
"00001000000000000000000000001000", -- 150
507
"00001000000000000000000000001000", -- 151
508
"00001000000000000000000000001000", -- 152
509
"00001000000000000000000000001000", -- 153
510
"00001000000000000000000000001000", -- 154
511
"00001000000000000000000000001000", -- 155
512
"00001000000000000000000000001010", -- 156
513
"00001000000000000000000000001000", -- 157
514
"00001000000000000000000000001000", -- 158
515
"00001000000000000000000000001000", -- 159
516
"00001000000000000000000000001000", -- 15a
517
"00001000000000000000000000001000", -- 15b
518
"00001000000000000000000000001000", -- 15c
519
"00001000000000000000000000001000", -- 15d
520
"00001000000000000000000000001010", -- 15e
521
"00001000000000000000000000001000", -- 15f
522
"00001000000000000000000000001000", -- 160
523
"00001000000000000000000000001000", -- 161
524
"00001000000000000000000000001000", -- 162
525
"00001000000000000000000000001000", -- 163
526
"00001000000000000000000000001000", -- 164
527
"00001000000000000000000000001000", -- 165
528
"00001000000000000000000000001010", -- 166
529
"00001000000000000000000000001000", -- 167
530
"00001000000000000000000000001000", -- 168
531
"00001000000000000000000000001000", -- 169
532
"00001000000000000000000000001000", -- 16a
533
"00001000000000000000000000001000", -- 16b
534
"00001000000000000000000000001000", -- 16c
535
"00001000000000000000000000001000", -- 16d
536
"00001000000000000000000000001010", -- 16e
537
"00001000000000000000000000001000", -- 16f
538
"00001000000000000000000000001100", -- 170
539
"00001000000000000000000000001100", -- 171
540
"00001000000000000000000000001100", -- 172
541
"00001000000000000000000000001100", -- 173
542
"00001000000000000000000000001100", -- 174
543
"00001000000000000000000000001100", -- 175
544
"00001000000000000000110000011000", -- 176
545
"00001000000000000000000000001100", -- 177
546
"00001000000000000000000000001000", -- 178
547
"00001000000000000000000000001000", -- 179
548
"00001000000000000000000000001000", -- 17a
549
"00001000000000000000000000001000", -- 17b
550
"00001000000000000000000000001000", -- 17c
551
"00001000000000000000000000001000", -- 17d
552
"00001000000000000000000000001010", -- 17e
553
"00001000000000000000000000001000", -- 17f
554
"00001000000000000000010000001000", -- 180
555
"00001000000000000000010000001000", -- 181
556
"00001000000000000000010000001000", -- 182
557
"00001000000000000000010000001000", -- 183
558
"00001000000000000000010000001000", -- 184
559
"00001000000000000000010000001000", -- 185
560
"00001000000000000000010000011000", -- 186
561
"00001000000000000000010000001000", -- 187
562
"00001000000000000000010000001010", -- 188
563
"00001000000000000000010000001010", -- 189
564
"00001000000000000000010000001010", -- 18a
565
"00001000000000000000010000001010", -- 18b
566
"00001000000000000000010000001010", -- 18c
567
"00001000000000000000010000001010", -- 18d
568
"00001000000000000000010000011010", -- 18e
569
"00001000000000000000010000001010", -- 18f
570
"00001000000000000000010000001100", -- 190
571
"00001000000000000000010000001100", -- 191
572
"00001000000000000000010000001100", -- 192
573
"00001000000000000000010000001100", -- 193
574
"00001000000000000000010000001100", -- 194
575
"00001000000000000000010000001100", -- 195
576
"00001000000000000000010000011100", -- 196
577
"00001000000000000000010000001100", -- 197
578
"00001000000000000000010000001110", -- 198
579
"00001000000000000000010000001110", -- 199
580
"00001000000000000000010000001110", -- 19a
581
"00001000000000000000010000001110", -- 19b
582
"00001000000000000000010000001110", -- 19c
583
"00001000000000000000010000001110", -- 19d
584
"00001000000000000000010000011110", -- 19e
585
"00001000000000000000010000001110", -- 19f
586
"00001000000000000000010000010000", -- 1a0
587
"00001000000000000000010000010000", -- 1a1
588
"00001000000000000000010000010000", -- 1a2
589
"00001000000000000000010000010000", -- 1a3
590
"00001000000000000000010000010000", -- 1a4
591
"00001000000000000000010000010000", -- 1a5
592
"00001000000000000000010000100000", -- 1a6
593
"00001000000000000000010000010000", -- 1a7
594
"00001000000000000000010000010010", -- 1a8
595
"00001000000000000000010000010010", -- 1a9
596
"00001000000000000000010000010010", -- 1aa
597
"00001000000000000000010000010010", -- 1ab
598
"00001000000000000000010000010010", -- 1ac
599
"00001000000000000000010000010010", -- 1ad
600
"00001000000000000000010000100010", -- 1ae
601
"00001000000000000000010000010010", -- 1af
602
"00001000000000000000010000010100", -- 1b0
603
"00001000000000000000010000010100", -- 1b1
604
"00001000000000000000010000010100", -- 1b2
605
"00001000000000000000010000010100", -- 1b3
606
"00001000000000000000010000010100", -- 1b4
607
"00001000000000000000010000010100", -- 1b5
608
"00001000000000000000010000100100", -- 1b6
609
"00001000000000000000010000010100", -- 1b7
610
"00001000000000000000010000010110", -- 1b8
611
"00001000000000000000010000010110", -- 1b9
612
"00001000000000000000010000010110", -- 1ba
613
"00001000000000000000010000010110", -- 1bb
614
"00001000000000000000010000010110", -- 1bc
615
"00001000000000000000010000010110", -- 1bd
616
"00001000000000000000010000100110", -- 1be
617
"00001000000000000000010000010110", -- 1bf
618
"00001000000000000000100000011011", -- 1c0
619
"00001000000000000000100000110000", -- 1c1
620
"00001000000000000000100000001010", -- 1c2
621
"00001000000000000000100000000100", -- 1c3
622
"00001000000000000000100000010101", -- 1c4
623
"00001000000000000000100000100110", -- 1c5
624
"00001000000000000000000000111000", -- 1c6
625
"00001000000000000000100000011100", -- 1c7
626
"00001000000000000000100000011011", -- 1c8
627
"00001000000000000000100000010111", -- 1c9
628
"00001000000000000000100000001010", -- 1ca
629
"00001000000000000000000000000000", -- 1cb
630
"00001000000000000000100000010101", -- 1cc
631
"00001000000000000000100000001100", -- 1cd
632
"00001000000000000000000000111010", -- 1ce
633
"00001000000000000000100000011100", -- 1cf
634
"00001000000000000000100000011011", -- 1d0
635
"00001000000000000000100000110000", -- 1d1
636
"00001000000000000000100000001010", -- 1d2
637
"00001000000000000000110000010001", -- 1d3
638
"00001000000000000000100000010101", -- 1d4
639
"00001000000000000000100000100110", -- 1d5
640
"00001000000000000000000000111100", -- 1d6
641
"00001000000000000000100000011100", -- 1d7
642
"00001000000000000000100000011011", -- 1d8
643
"00001000000000000000000000000000", -- 1d9
644
"00001000000000000000100000001010", -- 1da
645
"00001000000000000000110000001010", -- 1db
646
"00001000000000000000100000010101", -- 1dc
647
"00001000000000000000000000000000", -- 1dd
648
"00001000000000000000000000111110", -- 1de
649
"00001000000000000000100000011100", -- 1df
650
"00001000000000000000100000011011", -- 1e0
651
"00001000000000000000100000110000", -- 1e1
652
"00001000000000000000100000001010", -- 1e2
653
"00001000000000000000100000111000", -- 1e3
654
"00001000000000000000100000010101", -- 1e4
655
"00001000000000000000100000100110", -- 1e5
656
"00001000000000000000010000000000", -- 1e6
657
"00001000000000000000100000011100", -- 1e7
658
"00001000000000000000100000011011", -- 1e8
659
"00001000000000000000100000100010", -- 1e9
660
"00001000000000000000100000001010", -- 1ea
661
"00001000000000000000000000101100", -- 1eb
662
"00001000000000000000100000010101", -- 1ec
663
"00001000000000000000000000000000", -- 1ed
664
"00001000000000000000010000000010", -- 1ee
665
"00001000000000000000100000011100", -- 1ef
666
"00001000000000000000100000011011", -- 1f0
667
"00001000000000000000100000110100", -- 1f1
668
"00001000000000000000100000001010", -- 1f2
669
"00001000000000000000110000001001", -- 1f3
670
"00001000000000000000100000010101", -- 1f4
671
"00001000000000000000100000101011", -- 1f5
672
"00001000000000000000010000000100", -- 1f6
673
"00001000000000000000100000011100", -- 1f7
674
"00001000000000000000100000011011", -- 1f8
675
"00001000000000000000110000000100", -- 1f9
676
"00001000000000000000100000001010", -- 1fa
677
"00001000000000000000110000001000", -- 1fb
678
"00001000000000000000100000010101", -- 1fc
679
"00001000000000000000000000000000", -- 1fd
680
"00001000000000000000010000000110", -- 1fe
681
"00001000000000000000100000011100"  -- 1ff
682
 
683
);
684
 
685
-- end of microcode ROM
686
 
687
signal load_al :      std_logic; -- uinst field, load AL reg from rbank
688
signal load_addr :    std_logic; -- uinst field, enable external addr reg load
689
signal load_t1 :      std_logic; -- uinst field, load reg T1 
690
signal load_t2 :      std_logic; -- uinst field, load reg T2
691
signal mux_in :       std_logic; -- uinst field, T1/T2 input data selection
692
signal load_do :      std_logic; -- uinst field, pipelined, load DO reg
693
-- rb_addr_sel: uinst field, rbank address selection: (sss,ddd,pp,ra_field)
694
signal rb_addr_sel :  std_logic_vector(1 downto 0);
695
-- ra_field: uinst field, explicit reg bank address
696
signal ra_field :     std_logic_vector(3 downto 0);
697
signal rbank_data :   std_logic_vector(7 downto 0); -- rbank output
698
signal alu_output :   std_logic_vector(7 downto 0); -- ALU output
699
-- data_output: datapath output: ALU output vs. F reg 
700
signal data_output :  std_logic_vector(7 downto 0);
701
signal T1 :           std_logic_vector(7 downto 0); -- T1 reg (ALU operand)
702
signal T2 :           std_logic_vector(7 downto 0); -- T2 reg (ALU operand)
703
-- alu_input: data loaded into T1, T2: rbank data vs. DI
704
signal alu_input :    std_logic_vector(7 downto 0);
705
signal we_rb :        std_logic; -- uinst field, commands a write to the rbank
706
signal inhibit_pc_increment : std_logic; -- avoid PC changes (during INTA)
707
signal rbank_rd_addr: std_logic_vector(3 downto 0); -- rbank rd addr
708
signal rbank_wr_addr: std_logic_vector(3 downto 0); -- rbank wr addr
709
signal DO :           std_logic_vector(7 downto 0); -- data output reg
710
 
711
-- Register bank as an array of 16 bytes (asynch. LUT ram)
712
type t_reg_bank is array(0 to 15) of std_logic_vector(7 downto 0);
713
-- Register bank : BC, DE, HL, AF, [PC, XY, ZW, SP]
714
signal rbank :        t_reg_bank;
715
 
716
signal flag_reg :     std_logic_vector(7 downto 0); -- F register
717
-- flag_pattern: uinst field, F update pattern: which flags are updated
718
signal flag_pattern : std_logic_vector(1 downto 0);
719
signal flag_s :       std_logic; -- new computed S flag  
720
signal flag_z :       std_logic; -- new computed Z flag
721
signal flag_p :       std_logic; -- new computed P flag
722
signal flag_cy :      std_logic; -- new computed C flag
723
signal flag_cy_1 :    std_logic; -- C flag computed from arith/logic operation
724
signal flag_cy_2 :    std_logic; -- C flag computed from CPC circuit
725
signal do_cy_op :     std_logic; -- ALU explicit CY operation (CPC, etc.)
726
signal do_cy_op_d :   std_logic; -- do_cy_op, pipelined
727
signal do_cpc :       std_logic; -- ALU operation is CPC
728
signal do_cpc_d :     std_logic; -- do_cpc, pipelined
729
signal do_daa :       std_logic; -- ALU operation is DAA
730
signal flag_ac :      std_logic; -- new computed half carry flag
731
-- flag_aux_cy: new computed half carry flag (used in 16-bit ops)
732
signal flag_aux_cy :  std_logic;
733
signal load_psw :     std_logic; -- load F register
734
 
735
-- aux carry computation and control signals
736
signal use_aux :      std_logic; -- decoded from flags in 1st phase
737
signal use_aux_cy :   std_logic; -- 2nd phase signal
738
signal reg_aux_cy :   std_logic;
739
signal aux_cy_in :    std_logic;
740
signal set_aux_cy :   std_logic;
741
signal set_aux  :     std_logic;
742
 
743
-- ALU control signals -- together they select ALU operation
744
signal alu_fn :       std_logic_vector(1 downto 0);
745
signal use_logic :    std_logic; -- logic/arith mux control 
746
signal mux_fn :       std_logic_vector(1 downto 0);
747
signal use_psw :      std_logic; -- ALU/F mux control
748
 
749
-- ALU arithmetic operands and result
750
signal arith_op1 :    std_logic_vector(8 downto 0);
751
signal arith_op2 :    std_logic_vector(8 downto 0);
752
signal arith_op2_sgn: std_logic_vector(8 downto 0);
753
signal arith_res :    std_logic_vector(8 downto 0);
754
signal arith_res8 :   std_logic_vector(7 downto 0);
755
 
756
-- ALU DAA intermediate signals (DAA has fully dedicated logic)
757
signal daa_res :      std_logic_vector(8 downto 0);
758
signal daa_res8 :     std_logic_vector(7 downto 0);
759
signal daa_res9 :     std_logic_vector(8 downto 0);
760
signal daa_test1 :    std_logic;
761
signal daa_test1a :   std_logic;
762
signal daa_test2 :    std_logic;
763
signal daa_test2a :   std_logic;
764
signal arith_daa_res :std_logic_vector(7 downto 0);
765
signal cy_daa :       std_logic;
766
 
767
-- ALU CY flag intermediate signals
768
signal cy_in_sgn :    std_logic;
769
signal cy_in :        std_logic;
770
signal cy_in_gated :  std_logic;
771
signal cy_adder :     std_logic;
772
signal cy_arith :     std_logic;
773
signal cy_shifter :   std_logic;
774
 
775
-- ALU intermediate results
776
signal logic_res :    std_logic_vector(7 downto 0);
777
signal shift_res :    std_logic_vector(7 downto 0);
778
signal alu_mux1 :     std_logic_vector(7 downto 0);
779
 
780 49 ja_rd
 
781 2 ja_rd
begin
782
 
783
DI <= data_in;
784
 
785
process(clk)    -- IR register, load when uc_decode flag activates
786
begin
787
  if clk'event and clk='1' then
788
    if uc_decode = '1' then
789
      IR <= DI;
790
    end if;
791
  end if;
792
end process;
793
 
794
s_field <= IR(2 downto 0); -- IR field extraction : sss reg code
795
d_field <= IR(5 downto 3); -- ddd reg code
796
p_field <= IR(5 downto 4); -- pp 16-bit reg pair code   
797
 
798
 
799
--##############################################################################
800
-- Microcode sequencer
801
 
802
process(clk)    -- do_reset is reset delayed 1 cycle
803
begin
804
  if clk'event and clk='1' then
805
    do_reset <= reset;
806
  end if;
807
end process;
808
 
809
uc_flags1 <= ucode(31 downto 29);
810
uc_flags2 <= ucode(28 downto 26);
811
 
812
-- microcode address control flags are gated by do_reset (reset has priority)
813
uc_do_ret <= '1' when uc_flags2 = "011" and do_reset = '0' else '0';
814
uc_jsr    <= '1' when uc_flags2 = "010" and do_reset = '0' else '0';
815
uc_tjsr   <= '1' when uc_flags2 = "100" and do_reset = '0' else '0';
816
uc_decode <= '1' when uc_flags1 = "001" and do_reset = '0' else '0';
817
uc_end    <= '1' when (uc_flags2 = "001" or (uc_tjsr='1' and condition_reg='0'))
818
                  and do_reset = '0' else '0';
819
 
820
-- other microinstruction flags are decoded
821
uc_halt_flag  <= '1' when uc_flags1 = "111" else '0';
822
uc_halt   <= '1' when uc_halt_flag='1' and inta_reg='0' else '0';
823
uc_ei     <= '1' when uc_flags1 = "011" else '0';
824
uc_di     <= '1' when uc_flags1 = "010" or inta_reg='1' else '0';
825
-- clr_t1/2 clears T1/T2 when explicitly commanded; T2 and T1 clear implicitly 
826
-- at the end of each instruction (by uc_decode)
827
clr_t2    <= '1' when uc_flags2 = "001" else '0';
828
clr_t1    <= '1' when uc_flags1 = "110" else '0';
829
use_aux   <= '1' when uc_flags1 = "101" else '0';
830
set_aux   <= '1' when uc_flags2 = "111" else '0';
831
 
832
load_al <= ucode(24);
833
load_addr <= ucode(25);
834
 
835
do_cy_op_d <= '1' when ucode(5 downto 2)="1011" else '0'; -- decode CY ALU op
836
do_cpc_d <= ucode(0); -- decode CPC ALU op
837
 
838
-- uinst jump command, either unconditional or on a given condition
839
uc_do_jmp <= uc_jsr or (uc_tjsr and condition_reg);
840
 
841
vma <= load_addr;  -- addr is valid, either for memmory or io
842
 
843 19 ja_rd
-- assume the only uinst that does memory access in the range 0..f is 'fetch'
844
fetch <= '1' when uc_addr(7 downto 4)=X"0" and load_addr='1' else '0';
845
 
846 2 ja_rd
-- external bus interface control signals
847
io <= '1' when uc_flags1="100" else '0'; -- IO access (vs. memory)
848
rd <= '1' when uc_flags2="101" else '0'; -- RD access
849
wr <= '1' when uc_flags2="110" else '0'; -- WR access  
850
 
851
uc_jmp_addr <= ucode(11 downto 10) & ucode(5 downto 0);
852
 
853
uc_addr_sel <= uc_do_ret & uc_do_jmp & uc_decode & uc_end;
854
 
855
addr_plus_1 <= uc_addr + 1;
856
 
857
-- TODO simplify this!!
858
 
859
-- NOTE: when end='1' we jump either to the FETCH ucode ot to the HALT ucode
860
-- depending on the value of the halt signal.
861
-- We use the unregistered uc_halt instead of halt_reg because otherwise #end
862
-- should be on the cycle following #halt, wasting a cycle.
863
-- This means that the flag #halt has to be used with #end or will be ignored. 
864
 
865
with uc_addr_sel select
866
  next_uc_addr <= '0'&uc_ret_addr when "1000", -- ret
867
                  '0'&uc_jmp_addr when "0100", -- jsr/tjsr
868
                  '0'&addr_plus_1 when "0000", -- uaddr++
869
                  "000000"&uc_halt&"11"
870
                                  when "0001", -- end: go to fetch/halt uaddr
871
                  '1'&DI          when others; -- decode fetched address 
872
 
873
-- Note how we used DI (containing instruction opcode) as a microcode address
874
 
875
-- read microcode rom 
876
process (clk)
877
begin
878
  if clk'event and clk='1' then
879
    ucode <= rom(conv_integer(next_uc_addr));
880
  end if;
881
end process;
882
 
883
-- microcode address register
884
process (clk)
885
begin
886
  if clk'event and clk='1' then
887
    if reset = '1' then
888
      uc_addr <= X"00";
889
    else
890
      uc_addr <= next_uc_addr(7 downto 0);
891
    end if;
892
  end if;
893
end process;
894
 
895
-- ucode address 1-level 'return stack'
896
process (clk)
897
begin
898
  if clk'event and clk='1' then
899
    if reset = '1' then
900
      uc_ret_addr <= X"00";
901
    elsif uc_do_jmp='1' then
902
      uc_ret_addr <= addr_plus_1;
903
    end if;
904
  end if;
905
end process;
906
 
907
 
908
alu_op <= ucode(3 downto 0);
909
 
910
-- pipeline uinst field2 for 1-cycle delayed execution.
911
-- note the same rbank addr field is used in cycles 1 and 2; this enforces
912
-- some constraints on uinst programming but simplifies the system.
913
process(clk)
914
begin
915
  if clk'event and clk='1' then
916
    ucode_field2 <= do_cy_op_d & do_cpc_d & clr_t2 & clr_t1 &
917
                    set_aux & use_aux & rbank_rd_addr &
918
                    ucode(14 downto 4) & alu_op;
919
  end if;
920
end process;
921
 
922
--#### HALT logic
923
process(clk)
924
begin
925
  if clk'event and clk='1' then
926
    if reset = '1' or int_pending = '1' then --inta_reg
927
      halt_reg <= '0';
928
    else
929
      if uc_halt = '1' then
930
        halt_reg <= '1';
931
      end if;
932
    end if;
933
  end if;
934
end process;
935
 
936
halt <= halt_reg;
937
 
938
--#### INTE logic -- inte_reg = '1' means interrupts ENABLED
939
process(clk)
940
begin
941
  if clk'event and clk='1' then
942
    if reset = '1' then
943
      inte_reg <= '0';
944 49 ja_rd
      delayed_ei <= '0';
945 2 ja_rd
    else
946 49 ja_rd
      if (uc_di='1' or uc_ei='1') and uc_end='1' then
947
        --inte_reg <= uc_ei;
948
        delayed_ei <= uc_ei; -- FIXME DI must not be delayed
949 2 ja_rd
      end if;
950 49 ja_rd
      if uc_end = '1' then -- at the last cycle of every instruction...
951
        if uc_di='1' then  -- ...disable interrupts if the instruction is DI...
952
          inte_reg <= '0';
953
        else
954
          -- ...of enable interrupts after the instruction following EI
955
          inte_reg <= delayed_ei;
956
        end if;
957
      end if;
958 2 ja_rd
    end if;
959
  end if;
960
end process;
961
 
962
inte <= inte_reg;
963
 
964 39 ja_rd
-- interrupts are ignored when inte='0' but they are registered and will be
965
-- honored when interrupts are enabled
966 2 ja_rd
process(clk)
967
begin
968
  if clk'event and clk='1' then
969
    if reset = '1' then
970
      int_pending <= '0';
971
    else
972 39 ja_rd
      -- intr will raise int_pending only if inta has not been asserted. 
973
      -- Otherwise, if intr overlapped inta, we'd enter a microcode endless 
974
      -- loop, executing the interrupt vector again and again.
975
      if intr='1' and inte_reg='1' and int_pending='0' and inta_reg='0' then
976 2 ja_rd
        int_pending <= '1';
977
      else
978 39 ja_rd
        -- int_pending is cleared when we're about to service the interrupt, 
979
        -- that is when interrupts are enabled and the current instruction ends.
980 2 ja_rd
        if inte_reg = '1' and uc_end='1' then
981
          int_pending <= '0';
982
        end if;
983
      end if;
984
    end if;
985
  end if;
986
end process;
987
 
988
 
989
--#### INTA logic
990
-- INTA goes high from END to END, that is for the entire time the instruction
991
-- takes to fetch and execute; in the original 8080 it was asserted only for 
992
-- the M1 cycle.
993
-- All instructions can be used in an inta cycle, including XTHL which was
994
-- forbidden in the original 8080. 
995
-- It's up to you figuring out which cycle is which in multibyte instructions.
996
process(clk)
997
begin
998
  if clk'event and clk='1' then
999
    if reset = '1' then
1000
      inta_reg <= '0';
1001
    else
1002
      if int_pending = '1' and uc_end='1' then
1003
        -- enter INTA state
1004
        inta_reg <= '1';
1005
      else
1006
        -- exit INTA state
1007
        -- NOTE: don't reset inta when exiting halt state (uc_halt_flag='1').
1008
        -- If we omit this condition, when intr happens on halt state, inta
1009
        -- will only last for 1 cycle, because in halt state uc_end is 
1010
        -- always asserted.
1011
        if uc_end = '1' and uc_halt_flag='0' then
1012
          inta_reg <= '0';
1013
        end if;
1014
      end if;
1015
    end if;
1016
  end if;
1017
end process;
1018
 
1019
inta <= inta_reg;
1020
 
1021
 
1022
--##############################################################################
1023
-- Datapath
1024
 
1025
-- extract pipelined microcode fields
1026
ra_field <= ucode(18 downto 15);
1027
load_t1 <= ucode(23);
1028
load_t2 <= ucode(22);
1029
mux_in <= ucode(21);
1030
rb_addr_sel <= ucode(20 downto 19);
1031
load_do <= ucode_field2(7);
1032
set_aux_cy <= ucode_field2(20);
1033
do_clr_t1 <= ucode_field2(21);
1034
do_clr_t2 <= ucode_field2(22);
1035
 
1036
 
1037
-- T1 register 
1038
process (clk)
1039
begin
1040
  if clk'event and clk='1' then
1041
    if reset = '1' or uc_decode = '1' or do_clr_t1='1' then
1042
      T1 <= X"00";
1043
    else
1044
      if load_t1 = '1' then
1045
        T1 <= alu_input;
1046
      end if;
1047
    end if;
1048
  end if;
1049
end process;
1050
 
1051
-- T2 register
1052
process (clk)
1053
begin
1054
  if clk'event and clk='1' then
1055
    if reset = '1' or uc_decode = '1' or do_clr_t2='1' then
1056
      T2 <= X"00";
1057
    else
1058
      if load_t2 = '1' then
1059
        T2 <= alu_input;
1060
      end if;
1061
    end if;
1062
  end if;
1063
end process;
1064
 
1065
-- T1/T2 input data mux
1066
alu_input <= rbank_data when mux_in = '1' else DI;
1067
 
1068
-- register bank address mux logic
1069
 
1070
rbh <= '1' when p_field = "11" else '0';
1071
 
1072
with rb_addr_sel select
1073
  rbank_rd_addr <=  ra_field    when "00",
1074
                    "0"&s_field when "01",
1075
                    "0"&d_field when "10",
1076
                    rbh&p_field&ra_field(0) when others;
1077
 
1078
-- RBank writes are inhibited in INTA state, but only for PC increments.
1079
inhibit_pc_increment <= '1' when inta_reg='1' and use_aux_cy='1'
1080
                                 and rbank_wr_addr(3 downto 1) = "100"
1081
                                 else '0';
1082
we_rb <= ucode_field2(6) and not inhibit_pc_increment;
1083
 
1084
-- Register bank logic
1085
-- NOTE: read is asynchronous, while write is synchronous; but note also
1086
-- that write phase for a given uinst happens the cycle after the read phase.
1087
-- This way we give the ALU time to do its job.
1088
rbank_wr_addr <= ucode_field2(18 downto 15);
1089
process(clk)
1090
begin
1091
  if clk'event and clk='1' then
1092
    if we_rb = '1' then
1093
      rbank(conv_integer(rbank_wr_addr)) <= alu_output;
1094
    end if;
1095
  end if;
1096
end process;
1097
rbank_data <= rbank(conv_integer(rbank_rd_addr));
1098
 
1099
-- should we read F register or ALU output?
1100
use_psw <= '1' when ucode_field2(5 downto 4)="11" else '0';
1101
data_output <= flag_reg when use_psw = '1' else alu_output;
1102
 
1103
 
1104
process (clk)
1105
begin
1106
  if clk'event and clk='1' then
1107
    if load_do = '1' then
1108
        DO <= data_output;
1109
    end if;
1110
  end if;
1111
end process;
1112
 
1113
--##############################################################################
1114
-- ALU 
1115
 
1116
alu_fn <= ucode_field2(1 downto 0);
1117
use_logic <= ucode_field2(2);
1118
mux_fn <= ucode_field2(4 downto 3);
1119
--#### make sure this is "00" in the microcode when no F updates should happen!
1120
flag_pattern <=  ucode_field2(9 downto 8);
1121
use_aux_cy <= ucode_field2(19);
1122
do_cpc <= ucode_field2(23);
1123
do_cy_op <= ucode_field2(24);
1124
do_daa <= '1' when ucode_field2(5 downto 2) = "1010" else '0';
1125
 
1126
aux_cy_in <= reg_aux_cy when set_aux_cy = '0' else '1';
1127
 
1128
-- carry input selection: normal or aux (for 16 bit increments)?
1129
cy_in <= flag_reg(0) when use_aux_cy = '0' else aux_cy_in;
1130
 
1131
-- carry is not used (0) in add/sub operations
1132
cy_in_gated <= cy_in and alu_fn(0);
1133
 
1134
--##### Adder/substractor
1135
 
1136
-- zero extend adder operands to 9 bits to ease CY output synthesis
1137
-- use zero extension because we're only interested in cy from 7 to 8
1138
arith_op1 <= '0' & T2;
1139
arith_op2 <= '0' & T1;
1140
 
1141
-- The adder/substractor is done in 2 stages to help XSL synth it properly
1142
-- Other codings result in 1 adder + a substractor + 1 mux
1143
 
1144
-- do 2nd op 2's complement if substracting...
1145
arith_op2_sgn <=  arith_op2 when alu_fn(1) = '0' else not arith_op2;
1146
-- ...and complement cy input too
1147
cy_in_sgn <= cy_in_gated when alu_fn(1) = '0' else not cy_in_gated;
1148
 
1149
-- once 2nd operand has been negated (or not) add operands normally
1150
arith_res <= arith_op1 + arith_op2_sgn + cy_in_sgn;
1151
 
1152
-- take only 8 bits; 9th bit of adder is cy output
1153
arith_res8 <= arith_res(7 downto 0);
1154
cy_adder <= arith_res(8);
1155
 
1156
--##### DAA dedicated logic
1157
-- Note a DAA takes 2 cycles to complete! 
1158
 
1159
--daa_test1a='1' when daa_res9(7 downto 4) > 0x06
1160
daa_test1a <= arith_op2(3) and (arith_op2(2) or arith_op2(1) or arith_op2(0));
1161
daa_test1 <= '1' when flag_reg(4)='1' or daa_test1a='1' else '0';
1162
 
1163
process(clk)
1164
begin
1165
  if clk'event and clk='1' then
1166
    if reset='1' then
1167
      daa_res9 <= "000000000";
1168
    else
1169
      if daa_test1='1' then
1170
        daa_res9 <= arith_op2 + "000000110";
1171
      else
1172
        daa_res9 <= arith_op2;
1173
      end if;
1174
    end if;
1175
  end if;
1176
end process;
1177
 
1178
--daa_test2a='1' when daa_res9(7 downto 4) > 0x06 FIXME unused?
1179
daa_test2a <= daa_res9(7) and (daa_res9(6) or daa_res9(5) or daa_res9(4));
1180
daa_test2 <= '1' when flag_reg(0)='1' or daa_test1a='1' else '0';
1181
 
1182
daa_res <= '0'&daa_res9(7 downto 0) + "01100000" when daa_test2='1'
1183
           else daa_res9;
1184
 
1185
cy_daa <= daa_res(8);
1186
 
1187
-- DAA vs. adder mux
1188
arith_daa_res <= daa_res(7 downto 0) when do_daa='1' else arith_res8;
1189
 
1190
-- DAA vs. adder CY mux
1191
cy_arith <= cy_daa when do_daa='1' else cy_adder;
1192
 
1193
--##### Logic operations block
1194
logic_res <=  T1 and T2 when alu_fn = "00" else
1195
              T1 xor T2 when alu_fn = "01" else
1196
              T1 or  T2 when alu_fn = "10" else
1197
              not T1;
1198
 
1199
--##### Shifter
1200
shifter:
1201
for i in 1 to 6 generate
1202
begin
1203
  shift_res(i) <= T1(i-1) when alu_fn(0) = '0' else T1(i+1);
1204
end generate;
1205
shift_res(0) <= T1(7) when alu_fn = "00" else -- rot left 
1206
                cy_in when alu_fn = "10" else -- rot left through carry
1207
                T1(1); -- rot right
1208
shift_res(7) <= T1(0) when alu_fn = "01" else -- rot right
1209
                cy_in when alu_fn = "11" else -- rot right through carry
1210
                T1(6); -- rot left
1211
 
1212
cy_shifter   <= T1(7) when alu_fn(0) = '0' else -- left
1213
                T1(0);                          -- right
1214
 
1215
alu_mux1 <= logic_res when use_logic = '1' else shift_res;
1216
 
1217
 
1218
with mux_fn select
1219
  alu_output <= alu_mux1      when "00",
1220
                arith_daa_res when "01",
1221
                not alu_mux1  when "10",
1222
                "00"&d_field&"000" when others; -- RST  
1223
 
1224
--###### flag computation 
1225
 
1226
flag_s <= alu_output(7);
1227
flag_p <= not(alu_output(7) xor alu_output(6) xor alu_output(5) xor alu_output(4) xor
1228
         alu_output(3) xor alu_output(2) xor alu_output(1) xor alu_output(0));
1229
flag_z <= '1' when alu_output=X"00" else '0';
1230
flag_ac <= (arith_op1(4) xor arith_op2_sgn(4) xor alu_output(4));
1231
 
1232
flag_cy_1 <= cy_arith when use_logic = '1' else cy_shifter;
1233
flag_cy_2 <= not flag_reg(0) when do_cpc='0' else '1'; -- cmc, stc
1234
flag_cy <= flag_cy_1 when do_cy_op='0' else flag_cy_2;
1235
 
1236
flag_aux_cy <= cy_adder;
1237
 
1238
-- auxiliary carry reg
1239
process(clk)
1240
begin
1241
  if clk'event and clk='1' then
1242
    if reset='1' or uc_decode = '1' then
1243
      reg_aux_cy <= '1'; -- inits to 0 every instruction
1244
    else
1245
      reg_aux_cy <= flag_aux_cy;
1246
    end if;
1247
  end if;
1248
end process;
1249
 
1250
-- load PSW from ALU (i.e. POP AF) or from flag signals
1251
load_psw <= '1' when we_rb='1' and rbank_wr_addr="0110" else '0';
1252
 
1253
-- The F register has been split in two separate groupt that always update
1254
-- together (C and all others).
1255
 
1256
-- F register, flags S,Z,AC,P
1257
process(clk)
1258
begin
1259
  if clk'event and clk='1' then
1260
    if reset='1' then
1261
      flag_reg(7) <= '0';
1262
      flag_reg(6) <= '0';
1263
      flag_reg(4) <= '0';
1264
      flag_reg(2) <= '0';
1265
    elsif flag_pattern(1) = '1' then
1266
      if load_psw = '1' then
1267
        flag_reg(7) <= alu_output(7);
1268
        flag_reg(6) <= alu_output(6);
1269
        flag_reg(4) <= alu_output(4);
1270
        flag_reg(2) <= alu_output(2);
1271
      else
1272
        flag_reg(7) <= flag_s;
1273
        flag_reg(6) <= flag_z;
1274
        flag_reg(4) <= flag_ac;
1275
        flag_reg(2) <= flag_p;
1276
      end if;
1277
    end if;
1278
  end if;
1279
end procesS;
1280
 
1281
-- F register, flag C
1282
process(clk)
1283
begin
1284
  if clk'event and clk='1' then
1285
    if reset = '1' then
1286
      flag_reg(0) <= '0';
1287
    elsif flag_pattern(0) = '1' then
1288
      if load_psw = '1' then
1289
        flag_reg(0) <= alu_output(0);
1290
      else
1291
        flag_reg(0) <= flag_cy;
1292
      end if;
1293
    end if;
1294
  end if;
1295
end procesS;
1296
 
1297
flag_reg(5) <= '0'; -- constant flag
1298
flag_reg(3) <= '0'; -- constant flag
1299
flag_reg(1) <= '1'; -- constant flag
1300
 
1301
--##### Condition computation
1302
 
1303
condition_sel <= d_field(2 downto 0);
1304
with condition_sel select
1305
  condition <=
1306
            not flag_reg(6) when "000", -- NZ
1307
                flag_reg(6) when "001", -- Z
1308
            not flag_reg(0) when "010", -- NC
1309
                flag_reg(0) when "011", -- C
1310
            not flag_reg(2) when "100", -- PO
1311
                flag_reg(2) when "101", -- PE  
1312
            not flag_reg(7) when "110", -- P  
1313
                flag_reg(7) when others;-- M                  
1314
 
1315
 
1316
-- condition is registered to shorten the delay path; the extra 1-cycle
1317
-- delay is not relevant because conditions are tested in the next instruction
1318
-- at the earliest, and there's at least the fetch uinsts intervening.                
1319
process(clk)
1320
begin
1321
  if clk'event and clk='1' then
1322
    if reset = '1' then
1323
      condition_reg <= '0';
1324
    else
1325
      condition_reg <= condition;
1326
    end if;
1327
  end if;
1328
end process;
1329
 
1330
-- low byte address register
1331
process(clk)
1332
begin
1333
  if clk'event and clk='1' then
1334
    if reset = '1' then
1335
      addr_low <= X"00";
1336
    elsif load_al = '1' then
1337
      addr_low <= rbank_data;
1338
    end if;
1339
  end if;
1340
end process;
1341
 
1342
-- note external address registers (high byte) are loaded directly from rbank
1343
addr_out <= rbank_data & addr_low;
1344
 
1345
data_out <= DO;
1346
 
1347
end microcoded;
1348 19 ja_rd
 
1349
--------------------------------------------------------------------------------
1350
-- Timing diagram 1: RD and WR cycles
1351
--------------------------------------------------------------------------------
1352
--            1     2     3     4     5     6     7     8     
1353
--             __    __    __    __    __    __    __    __   
1354
-- clk      __/  \__/  \__/  \__/  \__/  \__/  \__/  \__/  \__
1355
--
1356 39 ja_rd
--          ==|=====|=====|=====|=====|=====|=====|=====|=====|
1357
--
1358 19 ja_rd
-- addr_o   xxxxxxxxxxxxxx< ADR >xxxxxxxxxxx< ADR >xxxxxxxxxxx
1359
--
1360
-- data_i   xxxxxxxxxxxxxxxxxxxx< Din >xxxxxxxxxxxxxxxxxxxxxxx
1361
--
1362
-- data_o   xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx< Dout>xxxxxxxxxxx
1363
--                         _____             _____
1364
-- vma_o    ______________/     \___________/     \___________
1365
--                         _____
1366
-- rd_o     ______________/     \_____________________________
1367
--                                           _____
1368
-- wr_o     ________________________________/     \___________
1369
--
1370
-- (functional diagram, actual time delays not shown)
1371
--------------------------------------------------------------------------------
1372
-- This diagram shows a read cycle and a write cycle back to back.
1373
-- In clock edges (4) and (7), the address is loaded into the external 
1374
-- synchronous RAM address register. 
1375
-- In clock edge (5), read data is loaded into the CPU.
1376
-- In clock edge (7), write data is loaded into the external synchronous RAM.
1377
-- In actual operation, the CPU does about 1 rd/wr cycle for each 5 clock 
1378
-- cycles, which is a waste of RAM bandwidth.
1379
--

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