verilog 系统函数

handucheng

麻烦帮我解释一下这个语句的意思，谢谢！

$setuphold(posedge CK &&& (flag == 1), posedge D, tsetup$D$CK, thold$D$CK, NOTIFIER);
    $setuphold(posedge CK &&& (flag == 1), negedge D, tsetup$D$CK, thold$D$CK, NOTIFIER);
    $width(negedge CK &&& (flag == 1), tminpwl$CK, 0, NOTIFIER);
    $width(posedge CK &&& (flag == 1), tminpwh$CK, 0, NOTIFIER);
    $period(posedge CK &&& (flag == 1), tperiod$CK, NOTIFIER);