Hi Richi,
You can checkout the T_busy functions here:
https://git.rtems.org/rtems/tree/cpukit/include/rtems/test.h#n2390
uint_fast32_t T_get_one_clock_tick_busy(void) gives you the busy count for one
tick.
You can then calculate the number of cycles you need to wait for you desired
certain time and pass it to: void T_busy(uint_fast32_t)
This should give you comparably accurate results over different platforms.
Best regards,
Jan
From: devel <devel-boun...@rtems.org> On Behalf Of Richi Dubey
Sent: Thursday, May 20, 2021 4:53 PM
To: rtems-de...@rtems.org <devel@rtems.org>
Subject: Writing code that takes time to run
Hi,
We are thinking of writing a piece of code that takes some time to run (it
would be amazing if it takes around 2 secs to run on hardware, but we would be
happy with something that takes a few milliseconds as well).
We tried writing this:
for(int i = 0; i<10000000; ++i){
fib2 = fib0 + fib1;
fib0 = fib1;
fib1 = fib2;
}
which takes few milliseconds when tested on qemu, but only takes few
microseconds on a real board. Do you have any suggestions of what else we can
do?
We want to write a code that is context switch safe (so, we can't simply check
the time before a loop, run an infinite loop that keeps checking current time
and stops after a few seconds - because this logic would fail if there happens
a context switch inside the loop and the task gets the control back after a few
seconds). We also don't want to do a wake_after() since we want the task to be
running on the cpu during the entire time (it is okay if the task gets
preempted due to a higher priority process), and not voluntarily giving the
control to some other task.
Any suggestions? The aim is to see the affect of a task getting removed from
the cpu due to task shifting by the newly arrived task (in strong apa vs non
task shifting scheduler).
Thank you.
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