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// 以一個8bit counter 做範例,說明不同的Verilog HDL 的寫法+ X8 p/ g+ t$ |6 r
// 對 cell area 所造成的差異.
, Z: T: ~$ o7 s3 d U0 B2 w
/ a7 Y1 _ {7 k9 `0 t`timescale 1 ns / 1 ns! ?# p6 S7 D3 m; i6 X; d3 M% i8 s
module cnt_8bit(
- C% B/ [3 M3 P0 e/ Q/ k. Y8 Y q ,
/ x, u2 }3 f, k3 o, M
. C, V; \6 W, V( x; o6 E8 D clk ,
' O" f: C; h5 }9 R n_reset,
. W }# K. D6 o) k: R* h enable ,- c5 q' J2 W5 j" R
down_en
4 X g2 c* J* U' Y8 q);& w9 X" c9 q! Q* Y' f6 K5 ~
output [7:0] q ;8 _0 u; t& r7 g
+ c5 {8 b, W- k) B
input clk ,
; N7 S# F M1 w, u, M) L+ V n_reset ,/ M0 S0 M! c7 X" P
enable ,4 v- X& E# y i4 |, k4 [( ?& Z7 A
down_en ;( d4 ], N4 D4 T S
4 q+ l% `3 u# u2 Y/ @6 ^ z
wire [7:0]2 d4 C$ a& {/ m" M4 S1 _
pq_combin ;
6 d3 }8 _! ~$ Z. I
- O. ?' a( i3 |- R/ l9 ]reg [7:0]9 H( f+ [8 f3 |( z# `- i' O9 \
q ;) ~$ t+ i( B3 o9 h
0 R& v. {$ w, l
7 f7 X; ]7 M z- Z( wassign
3 X. i) R* a, C- f |) R& r# w pq_combin[7:0] = ( {down_en ,enable} == 2'b01 ) ? (q[7:0] + 8'h01) :
7 s6 B, z p% J/ U( S" t. M9 Y- @. J ( {down_en ,enable} == 2'b11 ) ? (q[7:0] - 8'h01) : q[7:0] ;! _ F/ F; }) ]- w( i0 Z
7 I; B) X5 W6 ?+ k5 S4 c% p
: u) b$ m. V9 `( F5 I$ @
always @ ( posedge clk or negedge n_reset )9 \( W( A3 u9 k; H- S1 {
begin: O, d" _6 F6 e5 E9 F
if(~n_reset)
- O4 f. U2 h# y" R" f- r2 C# J begin' K( s+ J$ [# A4 k! W
q[7:0] <= #3 8'h00 ;
8 Q3 l' T9 I" M* Z7 q" B) Y end
& v9 D3 M6 o$ r9 @7 d else
, y. d5 e2 G# g8 s0 O begin
. }8 ?7 ]( b8 N3 O- W q[7:0] <= #3 pq_combin[7:0] ;
9 h {0 w0 U4 `" \ end
/ S6 H' v7 h' S( B' N+ _end
9 ^! T3 s: F* ~' M4 Dendmodule3 A- P- f3 Q( Q9 ~" Z+ \; r9 |
//---synthesize report for cell area --------------------------, u' B: ]( }9 P, v& `
Reference Library Unit Area Count Total Area Attributes3 R6 y0 D" z" z7 K( |8 F
-----------------------------------------------------------------------------
7 O9 G, J7 _) V# u7 e-----------------------------------------------------------------------------
3 D" @2 J1 u% _Total 10 references 403.000000
. R) G4 N* k, g& d' ^2 P2 T5 R7 z/ p- j, n
6 a1 d( O' |) X* M+ S6 M
// 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* |+ H! {# y' a0 Y// 混在一起寫. 這種寫法的RTL code , 經過Synthesize 後,會得到較大的 U' j$ z, [2 o
// Total cell area* u2 c6 ^' M; [
8 }0 C$ {8 ~) A+ R! t1 j
`timescale 1 ns / 1 ns; q$ F( [: m+ j; k5 ^. i* R% A
7 n3 ?( y \( d c; R+ cmodule cnt_8bit(
, I2 H5 f% k4 a/ Z q ,4 ~- ]3 M% L+ `8 R+ Y
% Z) L8 a! R4 ` clk ,: m6 [/ {* x6 d$ P4 e
n_reset,: t9 ^, v% G0 ^- p
enable ," z# L7 `6 E2 E1 d
down_en% |" y P: w8 W. c: W! F2 B* h
);
: G) \! |0 L$ Houtput [7:0] q ;! e) ~* @' x1 F% ~) H+ L# _/ }
/ {3 q+ n/ W" y6 E* \input clk ,( r, |! ?! G. S7 D
n_reset ,
' G8 s" Q, Z' d/ N enable ,. }$ @% B$ q0 v) R
down_en ;7 v1 D$ G/ m" w s, P% M" M) D) B
reg [7:0]0 `+ P1 _- P' w/ ~0 Y a
q ;# m' x/ j y( `0 f
, y' ]& d( B. }1 E! s! n
7 @2 d0 U- E# Z# _always @ ( posedge clk or negedge n_reset )6 c/ ]& U0 w$ p+ ?% L2 I1 ^$ j
begin! h H4 X7 U3 l7 x# i3 y$ W8 V( R
if(~n_reset)
. p/ }7 e7 k1 _5 {9 s begin* U' d' D4 M5 f6 s6 x
q[7:0] <= #3 8'h00 ;; h* d3 X! f) m6 V- V; U
end
' H$ C! h/ x) _# K else if( {down_en ,enable} == 2'b01 )9 y: Y O# F: |8 V( F
begin
" n1 G& w5 q) ]( O) F+ ` q[7:0] <= #3 q[7:0] + 8'h01 ;; \% D$ Y. M$ A. a( Z9 b; R
end2 T* O6 u* t* c, C1 D6 \0 j
else if( {down_en ,enable} == 2'b11 )( q: {0 J4 t$ n
begin
+ N# [5 ]& O8 h q[7:0] <= #3 q[7:0] - 8'h01 ;) ^$ ^- L4 t; e, L
end! x% a: k" N: Y) F/ x0 @
end$ f! `# H9 ^7 p( I4 i9 |
endmodule) f" h# s7 q7 {5 x- k% f
8 x2 N+ h' V% ~9 T5 z8 }0 F8 X
// ----------Synthesize report for cell area---------------
2 e: a+ P% T7 @6 s- r4 ZReference Library Unit Area Count Total Area Attributes
' _( H6 g2 [8 K/ ?% z3 i5 T8 R/ D1 F-----------------------------------------------------------------------------
- m6 u5 _: F T0 {" H-----------------------------------------------------------------------------. S* L! C9 O& T Y( F6 a2 l9 i
Total 10 references 403.0000009 G% h+ G) E/ r) A% @! G8 F
: K7 b- e$ E/ Q" k1 h) G2 R+ A( t
/****************************************************************************// l- i5 C1 F% ]* t
// 下面的寫法是將組合電路的部份,改用case~endcase 的方式完成,3 G0 M% e* v6 f/ \! g% Y
// total cell area 可以稍微減少一點而己.
* m/ R+ \( j3 T# F. k e% r% x8 k7 l( D4 ?2 ` m! r* N# _ R
`timescale 1 ns / 1 ns" W& d. u+ _ c2 H* e6 h% x
* K( ` i+ D* X; w( Cmodule cnt_8bit(
1 f, U* T' X# l8 k% e q ,& S9 a* Y6 \+ d+ \! u! ~& H
5 v% a8 s4 ?* J# n- [6 f clk ,
0 d4 i1 Z. S" o n_reset," V- K0 w* Q4 V2 G6 S& c. v: N4 H
enable ,
) q& K' z& l6 m( ^2 e1 ^( f( Z9 L down_en( Y# r! E8 K! ~4 d3 y: E
);
% M5 U% z: x+ ?output [7:0] q ;( L) |" W3 b8 U7 x9 `& x
; \/ {) Z" `3 P5 _: T7 f$ ?2 B7 Binput clk ,
4 ~ J& W( J: [( I, h n_reset ,2 |. |' Y2 g( Y
enable ,
3 I# L g5 X1 ?: T down_en ;
- U p1 A$ j, t0 N |+ C6 r% d- z2 y. _
reg [7:0]
: ?( n0 V R( w3 R q ,
7 v! g: O" P4 j9 ?& B9 z pq_combin ;3 R1 C8 r% v! B) w
, |0 T; |+ J p
! l" j- a. |0 }( r6 q; I+ F7 T. H
always @ (down_en or enable or q[7:0] )
! }3 S& E& P/ C8 Z3 Q/ wbegin
; k( ~6 r7 b6 w( C& y case({down_en ,enable}) // synopsys parallel_case full_case 7 x* [1 n* N0 [# O2 Z6 |' D) X
2'b01: pq_combin[7:0] = q[7:0] + 8'h01 ;4 v. u$ k5 j6 p
2'b11: pq_combin[7:0] = q[7:0] - 8'h01 ;
& a5 x" T" F* S5 v3 j: ? default: pq_combin[7:0] = q[7:0] ;( _) O# u3 H) V. z* O# Y
endcase: W0 ?* C7 F2 ^* U$ d6 {
end3 {0 J* E7 W" x0 F! D0 \3 F# Q
" g5 S K! W$ i$ {% x' c
/ J8 X# i9 X% d) q2 y
always @ ( posedge clk or negedge n_reset )9 e' p% W2 a1 ?: f7 o
begin
! m/ X) \' y2 _4 y5 m- x if(~n_reset)
' l5 v( l4 U1 W+ k* i/ M, {5 l: o% r begin
! P7 K7 a5 Y9 A0 d4 w q[7:0] <= #3 8'h00 ;" J! u/ o' [. }, U8 {
end& V- D+ d( M% v0 J N
else
; g( w* l& f* z begin; N; M S8 x9 P- A
q[7:0] <= #3 pq_combin[7:0] ;' B+ _" @5 u( m: Z p5 u1 ]3 e
end$ ~# r* I+ ]$ W/ q5 b
end
0 D: r2 [' ^) qendmodule
7 ?8 f! i+ C' S1 l- f" h// ----------Synthesize report for cell area---------------
+ ?+ n' D: A! F0 @: t' `$ CReference Library Unit Area Count Total Area Attributes" N8 c, T3 I9 h i3 J& K- R
-----------------------------------------------------------------------------
6 s/ D' R' i- w4 U-----------------------------------------------------------------------------# `4 d0 y8 |% Y# i# T( Q$ U: s
Total 11 references 399.000000 |
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