# 篇11-\$past构造与带时钟门控的\$past构造(Part 11 – \$past structure and \$past structure with clock gating)-其他

## 篇11-\$past构造与带时钟门控的\$past构造(Part 11 – \$past structure and \$past structure with clock gating)

1.\$past构造

SVA提供了一个内嵌的系统函数“\$past”，它可以得到信号在几个时钟周期之前的值。在默认情况下，它提供信号在前一个时钟周期的值。结构的基本语法如下：

\$past(signal_name, number of clock cycles)

这个任务能够有效地验证到达当前时钟周期的状态所采用的通路是正确的。

属性p19检验的是在给定的时钟上升沿，如果表达式（c&&d）为真，那么两个周期前，表达式（a&&b）为真。

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1. \$past structure

< strong > SVA < / strong > < strong > provides an embedded system function “\$past”, which can obtain the value of the signal before several clock cycles. By default, it provides the value of the signal in the previous clock cycle the basic syntax of the structure is as follows:

\$past(signal_name, number of clock cycles)

This task can effectively verify that the path used to reach the state of the current clock cycle is correct.

Property P19 checks that if the expression (C & amp; & amp; d) is true at the rising edge of a given clock, the expression (A & amp; & amp; b) is true two cycles ago.