1. assertion
assertion相关的 |->和 |=>的区别：
sequence_expr |-> property_expr : the end of sequence_expr is the start of property_expr.
sequence_expr |=> property_expr : the start of property_expr is 1 clock tick after the end of sequence_expr.
##0 indicates the beginning of the second sequence is the end of the first sequence.
##1 indicates the beginning of the second sequence is 1 clock tick later than the end of the first sequence.
seq1 ##[m:n] seq2 means seq2 must be true between m ~ n clock tick later than seq 1 is true.
$ means t the end of simulation.
intersect: seq1 intersect seq2, means seq1 and seq2 match at the same time.
throughout: exp1 throughout seq2, means exp1 must be true when seq2 is matched.
within: seq1 within seq2, means seq 1 must be matched during the period when seq2 is true.
2. rand
rand constraint
class A;
rand v;
constraint c_v{ v inside {0,1};}
endclass
A a;
a.c_v.constraint_mode(0); // 0-disable the rand constraint c_v.
%d 以及 %D 以十进制格式输出
%b 以及 %B 以二进制格式输出
%o 以及 %O 以八进制格式输出
%h 以及 %H 以十六进制格式输出
%s 以及 %S 以字符串格式输出
%c 以及 %C 以ASCII码格式输出
%v 以及 %V 输出线网类型变量的强度
%m 以及 %M 输出层次名
%t 以及 %T 以当前时间格式输出
%e 以及 %E 以指数表示方式输出实数(real型)
%f 以及 %F 以十进制数表示方式输出实数(real型)
%g 以及 %G 以十进制数或者以指数表示方式输出实数