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// 以一個8bit counter 做範例,說明不同的Verilog HDL 的寫法4 R2 G5 R2 E( d' ]% G
// 對 cell area 所造成的差異.
$ _0 n S- Y- O+ X9 e0 `2 P- x: J# _' ^
+ l9 `' f, _. ?9 v+ n2 J`timescale 1 ns / 1 ns" b7 T6 ^% X) X [( L
module cnt_8bit(
( F4 V5 U3 D ]6 M" ?, Q) i% i* U q ,
0 d" o* V# b0 [. ?# \. y; U: ~' l" C8 M
clk ,: N# l3 e4 ^, m
n_reset,
5 I' e( j) r$ `' @! ]5 G2 D( S enable ,
& }5 L* z) W% @' h# Q& H down_en* J2 q3 D) e; x# d) }+ f
);
4 ?# M% a; k/ o: _/ Goutput [7:0] q ;6 }0 L1 C4 Q k0 `/ Z: h4 f
! X' u4 R* D( t! w- d4 P) qinput clk ,) Q. l6 H R9 o( U
n_reset ,
; \/ v1 C' Z4 g# s: m enable ,
& [6 j* Q3 ^6 \1 P7 A0 Q! g down_en ;, k( d/ D# b7 v5 ]. H/ p
( q: n6 I% m, E% f, D5 M X
wire [7:0]: M- O$ Y& K5 c) \# R. U' F. g
pq_combin ;0 U/ Z% y, w1 N2 {
# {, d' P2 M5 Y* Y. hreg [7:0]
/ `: U! g# w. B+ ^2 N* j3 ] q ;4 w. C- f7 M6 O6 I5 e
* u. m8 Z6 Q, u) M! ]: X+ U
) k( d" U9 b; L* |- }% ]9 F) Kassign# [4 M7 v; x. H8 y. V- v
pq_combin[7:0] = ( {down_en ,enable} == 2'b01 ) ? (q[7:0] + 8'h01) :; \2 j/ _; |# n+ F0 N _
( {down_en ,enable} == 2'b11 ) ? (q[7:0] - 8'h01) : q[7:0] ;9 a9 M% Q" a7 ^& {- v
& z1 S. |% ]+ t) n4 z3 @ k0 d
6 ^. _5 U/ T/ N. V) Salways @ ( posedge clk or negedge n_reset )# Z% e: E4 ]" y
begin
* f; `8 H* a( e6 g% T U% ? if(~n_reset)
+ r3 R# U1 O x3 T begin
0 L* H% B i2 e$ L( R; ?: l q[7:0] <= #3 8'h00 ;& r; d3 U \7 P' E8 @( }' U- e$ V
end
+ i h* @- R( p n$ I9 h8 a9 j3 d else
: f, S9 h2 a, i( l- Y& J begin
8 j. M# }; v) v+ x0 G, [9 f3 y6 ^ q[7:0] <= #3 pq_combin[7:0] ;/ y# h, [9 V' M9 Y) b& G
end" h7 b/ q5 m4 ]7 r
end
% F; k# p- o0 M$ Tendmodule2 n- a. W6 \1 k8 d- ~3 Y0 n
//---synthesize report for cell area --------------------------/ r n- d) I* A* N
Reference Library Unit Area Count Total Area Attributes- Z( K" V. u u+ O6 ?) a' `
-----------------------------------------------------------------------------+ l& m! m0 s- n: X7 {7 M
-----------------------------------------------------------------------------
* V% x) U& _/ E8 M9 ?$ j, y+ YTotal 10 references 403.000000( s$ B2 r& E6 v; V
X9 q+ {$ ^/ r. [: F/ Q, V; e% d
1 g* e4 k! I5 m2 R$ ]+ x& W// 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* I6 L, n3 B( t/ d* N: ?$ D
// 混在一起寫. 這種寫法的RTL code , 經過Synthesize 後,會得到較大的. z4 i: {; i8 @7 W2 R7 S$ s" Z/ c( B
// Total cell area
& M# X/ Z! _: Q9 J& t. ]$ D- F b6 p- V$ p0 [) w& M+ E
`timescale 1 ns / 1 ns
5 u* s4 j' k7 }6 h; L. Y5 g7 L# X, B l$ _. v) F' j- @
module cnt_8bit(
2 D- L4 u3 P# ^" j) j q ,+ H2 \* N3 e2 R# m/ k" \5 s
! I: a/ c$ A+ x
clk ,
' f, k2 p+ _. s- | n_reset,
/ Y. o% B. i3 y: X enable ,: ]: [) B6 t3 p' P! r
down_en( f) ?& y$ I c; h& K
);# |8 K6 }" V- x" G- U, G6 j5 F
output [7:0] q ;0 v( g! h" F4 h1 U
1 Q$ P# F; P* V2 w6 Finput clk ,1 X* ~4 U6 z! f
n_reset ,7 \( F& G7 T! E9 l( {9 E8 s3 O8 s
enable ,5 P9 F. l5 ]- h# A$ \2 }/ H
down_en ;
: S+ O, |8 A3 T% A5 |1 L' `5 Ureg [7:0]
! O1 y3 _5 B( U6 d/ S/ d$ z7 z q ;
* u) P! F3 y# n! O V( ^9 k( D. N8 Z3 T# y. B* t
! K9 d! q. q7 c2 ?) E0 Valways @ ( posedge clk or negedge n_reset )1 V, i( u- F3 o4 ^
begin
7 J( T; v _1 Z if(~n_reset)
* s: f: a9 ^2 ^" |! H1 M begin
, ?7 T q, i/ @. K+ D q[7:0] <= #3 8'h00 ;( J* k& X& F i( K1 a& P/ R/ V
end
1 N5 e9 r; e4 w: q/ U5 H3 V4 R else if( {down_en ,enable} == 2'b01 )
6 t$ c" T" D+ d/ D begin
; o/ q" Q' ^! k: N" I q[7:0] <= #3 q[7:0] + 8'h01 ;$ G. L; z- a( }! M, P8 C* `4 G4 |
end
7 N7 E' @$ W* N( v else if( {down_en ,enable} == 2'b11 ): c! n7 S7 n1 E
begin
5 o. ]" x% i, J) k4 p$ c+ m. |7 ?1 g q[7:0] <= #3 q[7:0] - 8'h01 ;& y- q9 |, |. W$ p; F, w
end1 B1 g- j }* e6 b0 Y
end
* V }; c; ?( H2 Yendmodule! w3 c: ^& s( t
& V5 ~1 O' F; U7 d& ]+ b6 E1 F* v// ----------Synthesize report for cell area---------------, K' z% q- O' t
Reference Library Unit Area Count Total Area Attributes
% P8 O9 O6 a8 ~-----------------------------------------------------------------------------5 [9 b8 u$ K7 j* E, m
-----------------------------------------------------------------------------) P, ~% e% ? t9 |
Total 10 references 403.000000
7 L7 F1 K- E% D4 B' V9 k9 C( l3 Z- `
- g. C: b+ O8 k6 D& C) @/****************************************************************************/' |2 J6 u9 T7 C0 P3 E7 B
// 下面的寫法是將組合電路的部份,改用case~endcase 的方式完成, ]5 I# A2 f" [7 {# J' j
// total cell area 可以稍微減少一點而己.
5 T' M6 w, ]1 e% f0 g
; N1 \1 X( C9 ^* h. h5 w& `% o`timescale 1 ns / 1 ns
1 i+ O7 ^/ l- e6 c' ]8 R! @7 c) P/ F* e8 [% X
module cnt_8bit(
6 D7 n& V: v! E& b8 N. x q ,- r" v& H& u- p" `. K* }7 w
0 D& Q3 w7 {' y6 r' N" f
clk ,
& s" m$ J/ D- b5 X% ?0 ^5 c( m n_reset,4 L/ [6 I4 U7 N: [: D
enable ," `# `- C1 @4 D
down_en
" S+ ^$ J5 z4 |) ]: ]);- P% V5 O% f% i% o( I/ {
output [7:0] q ;
6 O7 i3 e( n% K5 h3 s& m& j" m/ H# D
input clk ,1 @: C3 v1 C! N+ [+ A) V
n_reset ,! p6 p; ^2 h4 v! X/ t& s, Y; m
enable ,
+ p4 i2 a6 y: s8 F down_en ;
( L* y) g9 h8 F' J
6 J" s1 k* G4 H, H4 X* t: m+ ureg [7:0]
$ L" [' @/ k* M( v9 S( a q ,
9 s O- ?0 W, R& M0 |5 x, G pq_combin ;
. v; n: d; U! Y7 m2 L
\! f$ S8 m3 }+ V$ P8 q' g1 n9 ~- D& u' i; Q0 M! D: A5 k: G
always @ (down_en or enable or q[7:0] )
' n7 T. g; Z3 T, Q0 f" |begin
7 l5 t( i/ s0 b) D4 B- J' b case({down_en ,enable}) // synopsys parallel_case full_case
! v0 p: o5 T6 [ 2'b01: pq_combin[7:0] = q[7:0] + 8'h01 ;
" C6 T3 }+ T6 Z( b, i8 L& B6 D 2'b11: pq_combin[7:0] = q[7:0] - 8'h01 ;
% w6 v2 l$ R# D. M default: pq_combin[7:0] = q[7:0] ;1 h( c; E0 {' @: X+ r
endcase* v9 y l+ k7 h1 t
end+ A, Z* q! w6 [5 w3 _4 y. W6 M* c
6 l3 W- K# @8 D, |6 `
4 B J9 Y" Q$ `always @ ( posedge clk or negedge n_reset )
8 j/ m; F; L7 |& B# l; ubegin
( p+ Y0 ~, @$ s) @5 K/ U7 l; L if(~n_reset); j0 I8 F# N# R- d) e: `
begin5 _5 [4 ^$ B) Z: r8 V
q[7:0] <= #3 8'h00 ;
! n' k4 k2 T) \. W+ O end) a& O5 |6 {# j& r0 U/ P
else
. f. C ~; r( A& O1 H7 U begin# M6 u9 g* n4 d/ k( J
q[7:0] <= #3 pq_combin[7:0] ;
, d y. ^. N7 _$ E end
# d: {1 q- B4 O! `. n& \ ?end" H {: t g+ g; t2 O/ F3 @" Z
endmodule- g& i1 ^, S4 \. q, C! ^' M( e
// ----------Synthesize report for cell area---------------3 ]5 A. A5 \2 W' a
Reference Library Unit Area Count Total Area Attributes X: ~0 r# J, d# X3 S
-----------------------------------------------------------------------------
a. G9 F$ ?# M6 X' m-----------------------------------------------------------------------------
9 [% I+ O f6 k3 g& d, X% X, x. G& n% eTotal 11 references 399.000000 |
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