On 11/14/2017 03:49 PM, Tommaso Saudelli wrote:
Hi, I'm writing since i am experiencing some difficulties through the development of an application which execute a cyclic task every 1 ms. The computer where this application should run is an embedded pc with an intel celeron j1900 quad core, 2G of ram and 32G of ssd. I have installed debian 9.2.1 on it, from a netinst iso image, with no graphical environment. I've downloaded the latest stable kernel source (4.9.47) with the respective rt patch (4.9.47-rt37) and followed the instructions as described in the web page "how to set up preempt_rt properly". I patched the kernel and then i ticked the box with the "Fully Preemptible Kernel" option, and compiled it (make, make modules_install, make install). Rebooted the pc, i checked that the new kernel was running (uname -a) and i wrote a small cpp application following the example of "how to build a simple rt application" web page and "how to build a basic cyclic application" web page.
Referencing web pages with names really isn't very helpful. These might be the right sites, and they might not be.
Then to be sure that the cycle keeps at a constant rate of 1 ms, i took the time in nano seconds (clock_gettime) each time the thread finished sleeping and woke up, and compared it with the previous woke up time by subtraction. In theory i should get this time to be around 1000000 ns, but what i get is that it varies continuosly from 800000 to 1100000. Sometimes when i launch the program it stays around the desired cycle time, but if i stop and restart the program then it starts to behave as before. I am really confused, what am i doing wrong or am i missing to do? Any suggestion is appreciated. Thanks in advance.
Without seeing your program, it is hard to say. It could be a lot of things.
-corey
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