01-08-2016 08:31 AM
Hello everyone,
I'm preparing for my CLED exam and I don't understand question 21 of the example exam.
The exam states that D is the right answer, but I don't understand why. The RT FIFO Read function clearly has a timeout of 100ms wired to it.
Why would the CPU speed go to 100%?
Thank you
Solved! Go to Solution.
01-08-2016 10:26 AM - edited 01-08-2016 10:27 AM
From the LabVIEW Help article Data Communication Methods in LabVIEW, an RT FIFO has a polling mode by default. Therefore, it will use as much CPU as possible looking for new data to come in instead of waiting for a notification that there is data. This is done to keep jitter at a minimum.
The DMA FIFO behaves the same way.
01-08-2016 10:41 AM - edited 01-08-2016 10:41 AM
I agree with crossrulz.
I don't quite like the question personally, since RT systems often have multiple cores these days. The RT FIFO Read function will poll for new data constantly and use up one core of CPU usage, but if the system has multiple cores this shows as 50% CPU usage in the case of two cores, and 25% in the case of four cores etc.
01-08-2016 10:47 AM
Craig_ wrote:
I don't quite like the question personally, since RT systems often have multiple cores these days. The RT FIFO Read function will poll for new data constantly and use up one core of CPU usage, but if the system has multiple cores this shows as 50% CPU usage in the case of two cores, and 25% in the case of four cores etc.
I does say "potential" issues. So with the assumption of 1 core, you will use 100% of the CPU. It is a question of knowing the nuances of how the RT FIFO works. Not saying the question is perfectly worded, etc. But it is not wrong.
01-11-2016 01:26 AM
Thank you very much.
04-08-2017 02:44 AM
Hi
I'm also preparing for my CLED, but I can't find a example part1 exam. Can you help me find the exam you used?
Thanks in advance
Kaare
04-08-2017 03:08 AM
Hey KJK!
You can find the Preparation E-kit here:
http://www.ni.com/gate/gb/GB_EKITCLEDPREP/US
Good luck sir.
04-08-2017 03:13 AM
I know, but there is not a part 1 example exam in there. I hopped you might have a copy of the prep kit you used?
Regards
Kaare
04-08-2017 03:36 AM
I can check on monday when I'm in the office, I will post it here if I still have it.
04-10-2017 06:54 AM
I've send you a PM.