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// 以一個8bit counter 做範例,說明不同的Verilog HDL 的寫法
1 M0 j0 k+ r8 U- f6 T! d% T// 對 cell area 所造成的差異.
7 Q# G7 [+ [# J, B% q
0 L |$ n0 Y3 z! r' P& d`timescale 1 ns / 1 ns
7 P4 [; m; @! b2 ?; I. u! C Vmodule cnt_8bit(
. o% @ a. J5 Z$ O0 g q ,
( a7 n7 r. N, ]& i* t4 G3 `' r5 r
clk ,
0 b% _8 [! Q9 v: Z3 T- C+ J$ b7 g2 G n_reset,6 y r# X: C9 `" S9 k; z F
enable ," @! W, k, V- q( k
down_en
$ ]; U' O% R; i% _) h);
3 i7 b! m) F4 K: G) c6 J5 Goutput [7:0] q ;; [1 c/ Y" d; [. h' V0 U) @
+ K) i9 r O5 I
input clk ,
w. F: ]- {8 o5 E6 ? n_reset ,3 b. Q7 J" K# }
enable ,4 z# ^5 F; R* _
down_en ;: g5 e- w* U' j
7 q/ R: K+ C6 j* U$ H0 ywire [7:0]! S! `$ h, U8 }, d% _5 i
pq_combin ;6 @2 W$ t. L! \, Q2 Y- k; a
6 s d, O3 L. ^& G- {7 v5 r preg [7:0]3 s" v7 b" i- l# M& n9 B4 e$ K
q ;
/ m1 D( _+ H6 J" B) B* @4 X) G1 k/ J" E: w. D/ A: a. i/ J% k3 e
' |: q5 i3 e! V& c5 q! C& g' nassign
; ~# Q' o0 b) I4 y( w( u pq_combin[7:0] = ( {down_en ,enable} == 2'b01 ) ? (q[7:0] + 8'h01) :
# X) @3 X1 }) u2 P ( {down_en ,enable} == 2'b11 ) ? (q[7:0] - 8'h01) : q[7:0] ;
: V) D% x( v- B
; O' V7 E* X p0 N% k! X) B! f( _3 x( A0 }$ N
always @ ( posedge clk or negedge n_reset )
+ k! L$ _- @* C4 W5 Hbegin6 X8 M9 x+ F: k4 o4 t
if(~n_reset)
2 [: v; U# {5 y ~ begin; _' {( c X) x0 }
q[7:0] <= #3 8'h00 ;7 g' V$ W2 A' b7 C, @2 q/ L
end
3 P: a1 o7 A! k6 t else
6 |- g, y/ |6 x+ P) T6 e begin7 d3 C1 `$ w0 r# h# K4 b
q[7:0] <= #3 pq_combin[7:0] ;
" q4 {8 ] Q. o' ~- \; P end
1 v+ A# G; B0 R! @0 V4 c yend
. k% e+ ?, u2 x' E E' \endmodule
! X' \3 s- u t& I//---synthesize report for cell area --------------------------
0 x' y- o6 s/ WReference Library Unit Area Count Total Area Attributes
. w0 z r& j6 P6 a, A9 X9 h-----------------------------------------------------------------------------
# g2 Q h! y. _: _-----------------------------------------------------------------------------
3 A7 Z3 H; \ W3 M% iTotal 10 references 403.000000- l4 d( M4 Y; J! ~6 ~* N1 V% Q& w
1 J' g/ ^; J" j3 w. c/ y! |3 S% Z& l- N! C- C' X3 i
// 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3 x5 s j9 g {5 C) X, f9 G5 g
// 混在一起寫. 這種寫法的RTL code , 經過Synthesize 後,會得到較大的
8 y, U0 }! K, n% j// Total cell area' j# M9 I+ l5 O" j/ U/ C
$ z8 K# v% ]+ C# O! a; ^" |`timescale 1 ns / 1 ns. Y+ ?9 ~2 O7 u# |3 b- Q
4 N0 x( k5 Z$ {( x$ umodule cnt_8bit(
* Z3 [/ }, a$ T+ [2 B. F q ,
! B: m) M. |0 [, Q0 d9 \, x$ `) j( O5 v; [/ j S: e" z
clk ,
7 u$ V1 `1 u! D9 B/ R/ m n_reset,
5 n$ d: q: z+ Z$ C enable ,
- b6 h; L+ P4 v6 B! R down_en( R. m- t$ s4 r+ k0 ~
);
4 F' p, n: V3 S E- Youtput [7:0] q ;
5 Z; Q& z- F" a9 }9 _9 q0 y
# [0 w* n" e" a7 n$ F4 linput clk ,
4 X7 p- N& M' a9 O+ X n_reset ,
9 U* b6 K7 P7 C) Q' `- ~ enable ,
9 |+ y3 m. x' ~3 z down_en ;
/ j" \4 m4 \" X3 k mreg [7:0]" G# @9 J/ m4 Z# }
q ;8 a2 P0 j$ ^' M4 `
& b- i3 w! t: S9 e6 x
0 R! o, N/ ]. I5 i5 p8 |2 H
always @ ( posedge clk or negedge n_reset )
- d1 N1 f- y" w3 [: }5 Mbegin" p" N0 I, |; X" ?9 x4 m* [( t
if(~n_reset)
! @$ R% p' ~& a- ? H begin6 k" Z0 @" G0 m1 ^4 x R
q[7:0] <= #3 8'h00 ;& P, r' E0 f( w% b1 b6 v
end9 \' H# H" R# _; Z3 N' L
else if( {down_en ,enable} == 2'b01 )
?0 w7 {5 O3 n& B3 o begin
4 a+ p' q+ M, [+ c; @9 P, {1 U4 G q[7:0] <= #3 q[7:0] + 8'h01 ;/ _4 j: ~4 W% Z0 ]: r x* x
end. B. V$ c7 m3 d
else if( {down_en ,enable} == 2'b11 ) \/ |* f* [/ r2 f* u' L! G( s
begin. R8 V( ]+ z" R, Y0 j! h3 y6 c
q[7:0] <= #3 q[7:0] - 8'h01 ;
8 H/ P) W4 l# p' t5 q J5 ` end7 k1 D/ N4 S* U$ w# z( r) v
end
8 q" u: E. B. J+ ?$ G" x& jendmodule* B! o2 \9 a/ P! ^! s1 X* i
1 F$ Z7 @* f7 {! n; k0 i: a7 }
// ----------Synthesize report for cell area---------------6 r: c5 l+ B# o& ^6 }' r7 k6 S
Reference Library Unit Area Count Total Area Attributes, X4 Z& S! c: x. Q
-----------------------------------------------------------------------------* Q: I- ^& T0 P
-----------------------------------------------------------------------------! Z0 ^8 b' P/ Y& p2 D
Total 10 references 403.000000# S( `, Q# D$ I8 j5 h8 [: w
' m+ j" r6 G) I$ w8 e
/****************************************************************************/
* m# W, v) f7 S0 ]' x% v" b' X// 下面的寫法是將組合電路的部份,改用case~endcase 的方式完成,7 t* p# H" w* e- w1 P
// total cell area 可以稍微減少一點而己.
' l! a1 H) p# ?' s7 B4 e! f0 r- o" g: ?0 Z$ f
`timescale 1 ns / 1 ns
4 G3 H1 p/ M! s. d
! N3 ~5 I7 J4 F# \; O/ U% W- \: K1 ^: ?module cnt_8bit(: z- n7 \7 ^6 t& \( ~5 G
q ,- T/ G( }9 O7 {9 K" |; t; @4 R
6 j' t. Z7 P! m, c8 A clk ,
7 I; R [$ M. q9 [% c2 p! _& f n_reset,
, `0 ~$ x- u7 M) c4 m: [" o enable ,
5 Q% e- d |2 p+ {" _1 ^ down_en; O$ ?( `, r% J) L* r
);
3 W" c8 E1 U* `0 n5 C, ?/ K6 `output [7:0] q ;
. U1 O. W: D3 S f& r7 t2 G6 E W$ z) V6 v& g% d) r, @
input clk ,
8 J5 h' }3 w* M- I# E) I% \2 E n_reset ,
, n% s9 j* |# t. R, ] enable ,' {: ]" b5 X& z' t
down_en ;
8 N; n0 J* p9 ]1 n
4 U! p" K& i( S1 q' [) n4 }7 freg [7:0]
$ t7 q8 c! A7 Q; o1 Q5 r q ,- g4 M7 z- u6 J: }
pq_combin ;
% a, |5 S: a; B! r8 j, m7 I
2 y/ _% _' n' S- _2 y9 a$ G3 e8 o& d4 U9 i7 }
always @ (down_en or enable or q[7:0] )
- w% g* M& x. T/ F( G) Y; W3 z& Gbegin
3 J$ h' F9 {4 ?: H' n5 L a case({down_en ,enable}) // synopsys parallel_case full_case % l: V- `( ]- p$ ]5 o8 B0 Q
2'b01: pq_combin[7:0] = q[7:0] + 8'h01 ; G* t+ P/ F" u, n' y8 D
2'b11: pq_combin[7:0] = q[7:0] - 8'h01 ;
0 z0 J7 B" }" K default: pq_combin[7:0] = q[7:0] ;
/ ~0 y' E9 V9 k9 `# o, U& H! o. o endcase
3 N5 r$ ~7 c! K9 w: d3 J6 Rend& W$ }/ @: h) }
& b! T# s' K- A5 q0 l- k- Q1 A
/ O5 n6 Q# \0 O" `$ talways @ ( posedge clk or negedge n_reset )
; m @/ E6 z, l# Y% j/ h0 A& D5 Sbegin1 ]* i( F8 T# Z
if(~n_reset)) p& V8 N+ V" n5 X6 L8 g! q" b
begin6 g" l) ~; ]* L& S6 u
q[7:0] <= #3 8'h00 ;
- M: ?( z/ b5 F7 j end
4 l9 u& J2 ^% k% x4 y4 u else5 ?8 j0 Y- |% J0 j% o* z& n
begin5 R& ^6 R$ m' a% ^6 D9 z) N
q[7:0] <= #3 pq_combin[7:0] ;
2 i6 h4 @( g/ [! Y9 `, A end9 Y( `3 P) k( C0 z
end
0 Y3 y' g2 D, X5 ^endmodule
) K* P# s4 a9 B. o: I// ----------Synthesize report for cell area---------------; h( @; P& A) j U
Reference Library Unit Area Count Total Area Attributes6 B1 f! ?# m4 C# \2 Q' j! \, e8 I
-----------------------------------------------------------------------------
4 \& {/ b4 J. D1 l2 m-----------------------------------------------------------------------------
$ O( L9 E% }2 X: V/ K9 oTotal 11 references 399.000000 |
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