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How do I control probe start/stop in ncsim from embedded CPU?

Ncsim User 1

I am running an RTL simulation with an embeddd CPU and some encryption logic. 

The CPU runs some codes to check the result of encryption logic and can run hours or days. 

My idea is to let the CPU control when to dump waveforms, likely when some conditions are met in the logic. Then stop when the conditon elapses. 

How should I do that? 

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  • The simplest way would be to use Tcl breakpoints to execute the probe commands when certain signal values are observed. For example, at the start of simulation, create the probe for the signals you want to debug, and give the probe a name, then immediately disable it (unless you want to probe at time 0):

    probe -create -shm -name myprobe <list_of_signals>
    probe -disable myprobe

    Then, create breakpoints to turn the probe on and off:

    stop -create -execute {probe -enable myprobe} -continue -condition {[value top.sig_to_start_probing] = 1'b1}
    stop -create -execute {probe -disable myprobe} -continue -condition {[value top.sig_to_start_probing] = 1'b0}

    There are many other types of breakpoints so you'll need to use your imagination to decide which is the most appropriate for your scenario.

    I would also suggest thinking about whether it's better to check the encryption result using some zero-time method in the testbench instead of having a simulated CPU to crunch the data, your tests would finish much quicker and be much easier to debug!

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