Skip to content

Commit 9076e3f

Browse files
TimRudyTimRudy
committed
More initial
- Update from functional to structural declaration using gates and wires
1 parent 969ad75 commit 9076e3f

File tree

1 file changed

+68
-215
lines changed

1 file changed

+68
-215
lines changed

‎source-7400/74181.v‎

Lines changed: 68 additions & 215 deletions
Original file line numberDiff line numberDiff line change
@@ -44,264 +44,117 @@ module ttl_74181 #(parameter WIDTH = 4, DELAY_RISE = 0, DELAY_FALL = 0)
4444
reg CP_computed;
4545
reg CG_computed;
4646
wire Equal_computed;
47-
reg C_in_bar;
48-
reg C_computed_bar;
4947
reg C_computed;
5048
reg [WIDTH-1:0] F_computed;
5149
wire [WIDTH-1:0] P_internal;
5250
wire [WIDTH-1:0] G_internal;
51+
wire [WIDTH-1:0] C_internal;
5352
wire [WIDTH-1:0] CG_internal;
5453

54+
// structural declaration using gates and wires (see datasheet for the schematic):
55+
5556
generate
5657
genvar i;
5758
for (i = 0; i < WIDTH; i = i + 1)
5859
begin: gen_internals
60+
wire [WIDTH-1:0] C_and_P_term;
61+
wire [WIDTH-1:0] P_and_G_term;
62+
wire [WIDTH-1:0] G_term;
63+
5964
// first layer: internal propagate and generate signals from each A, B bit pair
60-
// used for carry output C (in the logic section), and used for
61-
// carry lookahead outputs CP and CG
65+
// used for all further computations (function output F, carry output C,
66+
// carry lookahead outputs CP and CG)
6267
//
6368
assign P_internal[i] = ~(A_bar[i] & ~B_bar[i] & Select[2] | A_bar[i] & B_bar[i] & Select[3]);
6469
assign G_internal[i] = ~(A_bar[i] | B_bar[i] & Select[0] | ~B_bar[i] & Select[1]);
6570

66-
// second layer: internal carry generate signals from the propagate and generate signals,
67-
// used for carry lookahead output CG
71+
// second layer: internal carry signals from the carry in and propagate and generate signals,
72+
// used for computation of F bits (these are for arithmetic functions only;
73+
// for logic functions the Mode signal inhibits all C_internal outputs)
6874
//
69-
// the generated code has this structure (terms are then joined by |):
70-
// CG_internal[0] = P_internal[1] & P_internal[2] & P_internal[3] & G_internal[0];
71-
// CG_internal[1] = P_internal[2] & P_internal[3] & G_internal[1];
72-
// CG_internal[2] = P_internal[3] & G_internal[2];
73-
// CG_internal[3] = G_internal[3];
75+
// the generated code has this structure:
76+
// C_internal[0] = ~(C_in);
77+
// C_internal[1] = ~(C_in & P_internal[0] |
78+
// G_internal[0]);
79+
// C_internal[2] = ~(C_in & P_internal[0] & P_internal[1] |
80+
// P_internal[1] & G_internal[0] |
81+
// G_internal[1]);
82+
// C_internal[3] = ~(C_in & P_internal[0] & P_internal[1] & P_internal[2] |
83+
// P_internal[1] & P_internal[2] & G_internal[0] |
84+
// P_internal[2] & G_internal[1] |
85+
// G_internal[2]);
7486
//
75-
if (i < WIDTH - 1)
87+
if (i == 0)
7688
begin
77-
assign CG_internal[i] = (&P_internal[(WIDTH - 1):(i + 1)]) & G_internal[i];
89+
assign C_and_P_term[i] = C_in & !Mode;
7890
end
7991
else
8092
begin
81-
assign CG_internal[i] = G_internal[i];
82-
end
83-
end
84-
endgenerate
85-
86-
always @(*)
87-
begin
88-
if (!Mode)
89-
begin
90-
// arithmetic
91-
92-
C_in_bar = ~C_in;
93-
94-
// add (A PLUS B PLUS Carry)
95-
if (Select == 4'b1001)
96-
begin
97-
{C_computed_bar, F_computed} = {1'b0, A_bar} + {1'b0, B_bar} + C_in_bar;
98-
end
99-
100-
// subtract (A MINUS B MINUS 1 PLUS Carry)
101-
if (Select == 4'b0110)
102-
begin
103-
{C_computed_bar, F_computed} = {1'b0, A_bar} - {1'b0, B_bar} + {WIDTH{1'b1}} + C_in_bar;
104-
end
105-
106-
// other arithmetic incorporating logic
107-
108-
// A PLUS Carry
109-
if (Select == 4'b0000)
110-
begin
111-
{C_computed_bar, F_computed} = {1'b0, A_bar} + C_in_bar;
112-
end
113-
114-
// A OR B PLUS Carry
115-
if (Select == 4'b0001)
116-
begin
117-
{C_computed_bar, F_computed} = {1'b0, A_bar | B_bar} + C_in_bar;
118-
end
119-
120-
// A OR (NOT B) PLUS Carry
121-
if (Select == 4'b0010)
122-
begin
123-
{C_computed_bar, F_computed} = {1'b0, A_bar | ~B_bar} + C_in_bar;
124-
end
125-
126-
// MINUS 1 PLUS Carry
127-
if (Select == 4'b0011)
128-
begin
129-
{C_computed_bar, F_computed} = {WIDTH{1'b1}} + C_in_bar;
130-
end
131-
132-
// A PLUS (A AND (NOT B)) PLUS Carry
133-
if (Select == 4'b0100)
134-
begin
135-
{C_computed_bar, F_computed} = {1'b0, A_bar} + {1'b0, A_bar & ~B_bar} + C_in_bar;
136-
end
137-
138-
// (A OR B) PLUS (A AND (NOT B)) PLUS Carry
139-
if (Select == 4'b0101)
140-
begin
141-
{C_computed_bar, F_computed} = {1'b0, A_bar | B_bar} + {1'b0, A_bar & ~B_bar} + C_in_bar;
142-
end
143-
144-
// (A AND (NOT B)) MINUS 1 PLUS Carry
145-
if (Select == 4'b0111)
146-
begin
147-
{C_computed_bar, F_computed} = {1'b0, A_bar & ~B_bar} + {WIDTH{1'b1}} + C_in_bar;
148-
end
149-
150-
// A PLUS (A AND B) PLUS Carry
151-
if (Select == 4'b1000)
152-
begin
153-
{C_computed_bar, F_computed} = {1'b0, A_bar} + {1'b0, A_bar & B_bar} + C_in_bar;
154-
end
155-
156-
// (A OR (NOT B)) PLUS (A AND B) PLUS Carry
157-
if (Select == 4'b1010)
158-
begin
159-
{C_computed_bar, F_computed} = {1'b0, A_bar | ~B_bar} + {1'b0, A_bar & B_bar} + C_in_bar;
160-
end
161-
162-
// (A AND B) MINUS 1 PLUS Carry
163-
if (Select == 4'b1011)
164-
begin
165-
{C_computed_bar, F_computed} = {1'b0, A_bar & B_bar} + {WIDTH{1'b1}} + C_in_bar;
166-
end
167-
168-
// A PLUS A (SHIFT LEFT) PLUS Carry
169-
if (Select == 4'b1100)
170-
begin: sum_block
171-
reg [WIDTH:0] extra_width_sum;
172-
173-
extra_width_sum = A_bar << 1;
174-
175-
{C_computed_bar, F_computed} = extra_width_sum + C_in_bar;
176-
end
177-
178-
// A PLUS (A OR B) PLUS Carry
179-
if (Select == 4'b1101)
180-
begin
181-
{C_computed_bar, F_computed} = {1'b0, A_bar} + {1'b0, A_bar | B_bar} + C_in_bar;
182-
end
183-
184-
// A PLUS (A OR (NOT B)) PLUS Carry
185-
if (Select == 4'b1110)
186-
begin
187-
{C_computed_bar, F_computed} = {1'b0, A_bar} + {1'b0, A_bar | ~B_bar} + C_in_bar;
188-
end
189-
190-
// A MINUS 1 PLUS Carry
191-
if (Select == 4'b1111)
192-
begin
193-
{C_computed_bar, F_computed} = {1'b0, A_bar} + {WIDTH{1'b1}} + C_in_bar;
194-
end
195-
196-
C_computed = ~C_computed_bar;
197-
end
198-
else
199-
begin
200-
// logic
201-
202-
// NOT A
203-
if (Select == 4'b0000)
204-
begin
205-
F_computed = ~A_bar;
206-
end
207-
208-
// NOT (A OR B)
209-
if (Select == 4'b0001)
210-
begin
211-
F_computed = ~(A_bar | B_bar);
212-
end
93+
localparam i_minus_1 = i - 1;
21394

214-
// (NOT A) AND B
215-
if (Select == 4'b0010)
216-
begin
217-
F_computed = ~A_bar & B_bar;
218-
end
95+
assign C_and_P_term[i] = C_in & (&P_internal[i_minus_1:0]) & !Mode;
21996

220-
// 0
221-
if (Select == 4'b0011)
222-
begin
223-
F_computed = {WIDTH{1'b0}};
224-
end
97+
assign G_term[i] = G_internal[i_minus_1] & !Mode;
22598

226-
// NOT (A AND B)
227-
if (Select == 4'b0100)
228-
begin
229-
F_computed = ~(A_bar & B_bar);
230-
end
99+
if (i > 1)
100+
begin
101+
genvar j;
102+
for (j = 0; j < i_minus_1; j = j + 1)
103+
begin: gen_P_and_G_term
104+
localparam j_plus_one = j + 1;
231105

232-
// NOT B
233-
if (Select == 4'b0101)
234-
begin
235-
F_computed = ~B_bar;
106+
// these terms will be joined by | below:
107+
assign P_and_G_term[j] = (&P_internal[i_minus_1:j_plus_one]) & G_internal[j] & !Mode;
108+
end
109+
end
236110
end
237111

238-
// A XOR B
239-
if (Select == 4'b0110)
112+
// internal carry signals aggregated from the above terms
113+
if (i == 0)
240114
begin
241-
F_computed = A_bar ^ B_bar;
115+
assign C_internal[i] = ~C_and_P_term[i];
242116
end
243-
244-
// A AND (NOT B)
245-
if (Select == 4'b0111)
246-
begin
247-
F_computed = A_bar & ~B_bar;
248-
end
249-
250-
// (NOT A) OR B
251-
if (Select == 4'b1000)
252-
begin
253-
F_computed = ~A_bar | B_bar;
254-
end
255-
256-
// NOT (A XOR B)
257-
if (Select == 4'b1001)
117+
else if (i == 1)
258118
begin
259-
F_computed = ~(A_bar ^ B_bar);
119+
assign C_internal[i] = ~(C_and_P_term[i] | G_term[i]);
260120
end
261-
262-
// B
263-
if (Select == 4'b1010)
264-
begin
265-
F_computed = B_bar;
266-
end
267-
268-
// A AND B
269-
if (Select == 4'b1011)
270-
begin
271-
F_computed = A_bar & B_bar;
272-
end
273-
274-
// 1
275-
if (Select == 4'b1100)
276-
begin
277-
F_computed = {WIDTH{1'b1}};
278-
end
279-
280-
// A OR (NOT B)
281-
if (Select == 4'b1101)
121+
else
282122
begin
283-
F_computed = A_bar | ~B_bar;
123+
assign C_internal[i] = ~(C_and_P_term[i] | (|P_and_G_term[(i - 2):0]) | G_term[i]);
284124
end
285125

286-
// A OR B
287-
if (Select == 4'b1110)
126+
// second layer, separate section: internal carry generate signals from the
127+
// propagate and generate signals, used for computation of:
128+
// carry output C, carry lookahead output CG
129+
//
130+
// the generated code has this structure (terms are then joined by |):
131+
// CG_internal[0] = P_internal[1] & P_internal[2] & P_internal[3] & G_internal[0];
132+
// CG_internal[1] = P_internal[2] & P_internal[3] & G_internal[1];
133+
// CG_internal[2] = P_internal[3] & G_internal[2];
134+
// CG_internal[3] = G_internal[3];
135+
//
136+
if (i < WIDTH - 1)
288137
begin
289-
F_computed = A_bar | B_bar;
138+
assign CG_internal[i] = (&P_internal[(WIDTH - 1):(i + 1)]) & G_internal[i];
290139
end
291-
292-
// A
293-
if (Select == 4'b1111)
140+
else
294141
begin
295-
F_computed = A_bar;
142+
assign CG_internal[i] = G_internal[i];
296143
end
297-
298-
// third layer: carry bit
299-
C_computed = C_in & (&P_internal) | (|CG_internal);
300144
end
145+
endgenerate
301146

147+
always @(*)
148+
begin
302149
// third layer: carry lookahead bits aggregated from the above terms
303150
CP_computed = ~(&P_internal);
304151
CG_computed = ~(|CG_internal);
152+
153+
// third layer: carry bit
154+
C_computed = C_in & (&P_internal) | (|CG_internal);
155+
156+
// third layer: F bits
157+
F_computed = P_internal ^ G_internal ^ C_internal;
305158
end
306159

307160
// output

0 commit comments

Comments
 (0)