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// 以一個8bit counter 做範例,說明不同的Verilog HDL 的寫法
2 Z3 V) ~/ M6 [ [1 \$ S; ~// 對 cell area 所造成的差異.
: ?1 q, N0 S, D" [) E( W4 C% p2 W( \2 A: x$ X2 p2 M
`timescale 1 ns / 1 ns% `7 b7 o: m4 l* \: D: i
module cnt_8bit(- d8 d* k O- f. a: O* h
q ,0 O8 K7 h( K0 H! G
: w% t; _% P, k. y2 h
clk ,; ^' _$ ^$ r. [, ^
n_reset,
, K; `1 B( E9 w% y enable ,
`: N3 u& i5 i down_en
3 z6 X7 f6 c: X; w);+ m( j8 j1 U! a3 P- n; O
output [7:0] q ;
* n5 j7 m" B' W/ F( \( {
- k8 z+ V! O$ v$ p" u! N3 D$ r7 E0 Binput clk ,
6 M' y+ h$ n% @% F n_reset ,# F0 V$ `6 Y. q
enable ,
8 u" Y. @3 Y7 i6 m P" t4 P, e+ k down_en ;' R* j4 C: U6 L/ i
/ s5 p2 m6 n" I
wire [7:0]
7 u2 s& i" y3 R% K9 z# {1 M T pq_combin ;6 m" B9 y. u& U5 u Y4 p: @1 b( D
3 |; X7 g8 t+ z8 F( Ureg [7:0]
" S$ t3 t" a" a$ g# I# ^ q ;
, Z' h+ `) W* x i" P T
# v9 t( V+ C* Y- `3 G5 A' T0 l( j3 B
assign5 a/ t# s* C! f2 a7 S
pq_combin[7:0] = ( {down_en ,enable} == 2'b01 ) ? (q[7:0] + 8'h01) :
3 S4 T1 |( w$ k6 X! S6 J& h, Q. ] ( {down_en ,enable} == 2'b11 ) ? (q[7:0] - 8'h01) : q[7:0] ;
% y; T) z9 a" B$ A7 h& n+ |
7 z$ m5 @0 h% o9 F, i( n9 ^; }, r. t, _: R$ T: |; Z
always @ ( posedge clk or negedge n_reset )2 k9 S2 v+ ?" ] X/ F/ M
begin/ N; l Z" d+ `
if(~n_reset)+ K/ Z& ?$ i1 A
begin
7 m% e# C# ~6 g# r* F' y q[7:0] <= #3 8'h00 ;
7 B0 g! ^( u, Q- _$ X6 P end
. T5 C3 R4 P6 s* [( N else3 O0 F- o" h' O& M, x. ?1 @9 y: x
begin+ \% R+ R2 I' @8 X9 o
q[7:0] <= #3 pq_combin[7:0] ;1 c7 ]0 M4 Q1 E
end1 X5 N# `( R) T2 @0 x- z4 R1 m
end6 h9 B: Y: D! Z; E ?3 x
endmodule1 Z+ z) [ K4 c1 X# j
//---synthesize report for cell area --------------------------
3 ]7 J: X7 d; a( v: lReference Library Unit Area Count Total Area Attributes* V' l* W' s6 Y, I0 ^
-----------------------------------------------------------------------------
" N8 B M8 S% Q2 p* D-----------------------------------------------------------------------------$ Z: P% e6 a5 |) Z1 z& ]+ B
Total 10 references 403.000000
! v! I2 Z2 [) N- @5 m% G+ H$ J$ y% h( C2 O0 N" w2 N
% Y& v& a' V" B7 z! c7 e; n! t
// 考量到易於理解閱讀,及修改維護,大部份的IC Designer ,都將循序電路及組合電路& S% N& g% i" l8 v0 f3 o
// 混在一起寫. 這種寫法的RTL code , 經過Synthesize 後,會得到較大的
4 ?( i& @1 Z, H# J; J5 O. @// Total cell area
8 e( W# { \! |* q0 d: a
8 {& a) x1 V, q" S; `) c6 ~`timescale 1 ns / 1 ns1 p& D- ]6 r2 h0 M
- J9 E- S; O" ^1 E3 R m
module cnt_8bit(6 r$ p* ^7 B# ~" ^" j
q ,# z5 c5 L# ^, l6 J( \3 d
, q8 @) d- n; O/ _# H
clk ,
$ j2 ^# R: q- ^6 }* J9 ~3 E$ U n_reset,
+ Q5 P, T8 E( T enable ,
, T2 H+ q' w/ v" Q" Z7 [8 G down_en$ A# _. r0 M7 Z5 ?* D4 U: c9 ]# R
);
: Z, J8 t" R& h. joutput [7:0] q ;
1 O9 l' h' b* j; u1 z5 c
' d6 W8 r8 Z6 n- Hinput clk ,7 A3 E: W9 ]1 ^, X* b
n_reset , p, B: A$ \7 P( g5 G# T- x
enable ,- y/ `7 N4 r0 |& q4 E6 [! ^% Z, [
down_en ;4 b# ^2 _. Y8 g8 O2 Y
reg [7:0]- u+ D, O3 N8 b0 @
q ;% L6 G. E$ ^% x, @! t" Z9 Y
+ a9 B, e* m* B5 q! _6 j. }: {. X. `. T
always @ ( posedge clk or negedge n_reset )
+ o0 U" g' J+ Q& q* \begin
+ o8 Q/ g- y8 Q5 D2 k if(~n_reset)
; y" E/ N3 f1 T begin- t: C+ c' J6 O
q[7:0] <= #3 8'h00 ;
; [1 E/ I' H2 f, h2 ? end; U8 O" q2 K& u9 `0 D
else if( {down_en ,enable} == 2'b01 )3 s4 N! J7 T# B4 F! C3 U5 g$ t6 P
begin
$ s1 q( G/ g. w6 l% ] q[7:0] <= #3 q[7:0] + 8'h01 ;
B/ j, V3 m- V4 k end' D' K$ `* ]4 ]4 D% f3 |- j4 m( |
else if( {down_en ,enable} == 2'b11 )
% B6 ^8 f( i9 r. M# m begin
* E3 x5 C7 ]$ v6 e- H x q[7:0] <= #3 q[7:0] - 8'h01 ;
+ d l; b0 @& H! C' D; a end4 x9 d7 s" F) k: A3 k
end9 j6 |6 Z9 }) V& l& r, i8 I
endmodule
j" x: y, L/ w0 c$ Z; p/ I
! P6 m, p4 E4 K' l1 h// ----------Synthesize report for cell area---------------- D$ H/ h9 L/ v* x* d
Reference Library Unit Area Count Total Area Attributes
4 S; n4 X+ m1 R2 l3 u" V+ w-----------------------------------------------------------------------------
; f$ H' y3 V4 U- }- p$ I* @-----------------------------------------------------------------------------3 y! N$ f0 O6 l5 P. T6 F
Total 10 references 403.000000
2 S0 q, o8 S' J1 x2 o6 j: o2 K+ ~! @( t; q4 O% J& I
/****************************************************************************/) m# i# S: c: o
// 下面的寫法是將組合電路的部份,改用case~endcase 的方式完成,; w& u5 Q7 `( ]6 _8 d( E
// total cell area 可以稍微減少一點而己.5 j T6 n3 O! p8 n+ V" z
& n* t0 R% n6 F! s6 Q`timescale 1 ns / 1 ns
* _0 s( L6 l$ v, K& V3 H4 _6 Z0 O
% K( C( \; r3 [% S7 i) Nmodule cnt_8bit(. o5 n0 {! I) g& G9 `7 F/ h2 c. G
q ,. ^+ i8 W9 J7 i/ S' X
4 B( ^9 B+ F, J* @/ t( ]
clk ,* i: w; B! D& T4 G' |7 u: }9 n
n_reset," U, b- {& }8 D6 w4 k/ u
enable ,
* W2 {/ L0 k4 t. Z; R3 V down_en
/ Y/ O( c7 [$ m7 E4 p: \4 y);
2 G. q& X# E$ N I5 R+ X* P7 h. Qoutput [7:0] q ;7 }( I# l, `' d8 U1 U9 K
( p( H/ v6 W6 [+ Hinput clk ,
, C# |3 F; x! a; w6 e7 U n_reset ,# x% D& q4 {0 R3 i% V2 _9 ]% h
enable ,
& a4 |# Y! y7 U6 d3 d, p down_en ;
7 M4 ^, d/ y2 q* m8 u0 @5 C
+ Y; r) ^5 c& t( H$ Dreg [7:0]
" ]$ Q7 `; k$ K. {0 ` q ,
4 {0 c3 b3 R& p. D+ M pq_combin ;
/ b8 q& J V- T3 y: j. L) @5 t' u2 o4 |$ Y$ W: Z+ w: z
; X4 l% _% s7 f" W
always @ (down_en or enable or q[7:0] )
7 W, ]% q u9 K ^4 Pbegin
* z8 i" I$ z8 ^9 W6 p case({down_en ,enable}) // synopsys parallel_case full_case 7 E$ u" s$ H' e9 [! p* N6 `
2'b01: pq_combin[7:0] = q[7:0] + 8'h01 ;
1 p7 w' p# ?, O7 a/ h/ m* L 2'b11: pq_combin[7:0] = q[7:0] - 8'h01 ;6 E, V9 ^: b, Y9 O; ~
default: pq_combin[7:0] = q[7:0] ; u2 S% z0 S3 `: M8 B
endcase
$ }( ]* |7 k p8 X# S% dend% J. k& P0 W0 o( {
, O, ~3 \& d. W: V H" W
; @' \& W- c' n4 j" {* y. }% T5 Oalways @ ( posedge clk or negedge n_reset )
+ Q. P' {! x+ N! b( Ybegin0 G6 _9 K! Z, ]. u) v
if(~n_reset): O" l0 A- O# y
begin* M/ _4 k1 F9 L0 o
q[7:0] <= #3 8'h00 ;" r7 h9 m+ L1 K6 r
end$ ?: Z$ M3 f% f/ k5 A
else& @3 g+ a ?9 V: Q; o0 H6 K
begin
' I: v4 |: C. n! G4 N+ M9 c q[7:0] <= #3 pq_combin[7:0] ;$ I5 [+ _$ l v/ {; p
end
3 w1 l" M' n7 Tend
- ?& v- l' Z8 ~endmodule
/ y A* T: g0 g// ----------Synthesize report for cell area---------------
2 k, M: r- g$ Z& VReference Library Unit Area Count Total Area Attributes9 B) V6 w$ p& ^" s4 N( l: M
------------------------------------------------------------------------------ G5 A) G0 x" b9 x9 }$ D
------------------------------------------------------------------------------ j( L8 ~, `% t+ J8 N0 c; @
Total 11 references 399.000000 |
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