Certification
CLED example exam question 21
Solved!
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 
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.
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.
Hey KJK!
You can find the Preparation E-kit here:
http://www.ni.com/gate/gb/GB_EKITCLEDPREP/US
Good luck sir. 
