In reply to dave_59:
Thanks for the reply.
Requirement is to generate the clock and data within a sequence with continuous clock, So tried with forever and yes i agree it is not coming out of the forever loop.
In the 2nd snippet of code, 1st thread and 2nd thread is running parallelly but with time delay. when it shifts from 1st thread to 2nd and come back to the 1st it takes time. due to this clock period is getting affected from 100ns period to 87ns only during PCIe transactions.
2nd thread basically a PCIe transaction used by questa QVIP - mentor (rc_serial), it is a read/write transaction nearly takes 1us time/transaction. i am not sure due to pcie it takes time delay or not.
But when simple task is called in 2nd thread instead of PCIe read/write it is also taking some delay , due to that clock generation affect only during 2nd thread/task is in execution.
i tried to upload a waveform but not successful.