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Old 11-16-2004, 12:31 AM   #1
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Registered: Nov 2004
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Question Need to disable timer or all interrupts from user space

I'm not sure if this is the right place to ask this question but here you go.

I have implemented a very fast (8KHz loops) PID controller in user
space. I am getting the time from gettimeofday(). I use usleep to
complete the loop (125us).
When I dump the time values, I have loops that are over 125us. The
system is soft_RT (99.9% it is within 125us). However, every 1sec I
have very long loops (400us) and other 200us loops move often.
I think these are due to the timer interrupt. Timer interrupt is
suppose to be every 10ms in my kernel version (2.4.18). But somehow
it needs longer servicing once every second.
So, in order to get rid of these, I think I need to make a kernel
loadable module and that I can call to disable timer interrupt from
user space, then make another call to enable the timer interrupt
(maybe even disable/enable all interrupts). The
problem is I have not written KLM before. It seems that it is easy
to do in this case. But I don't know how to make the module
accessible from user space (how to make the call the
mydisable/myenable). If anyone has done this and has it handy, it
will be a lot of help!
Also, since my control loops is dependant from micro-second time
resolution, I am afraid that when I re-enable the timer interrupt, I
may have time "jumps". Is this true? BTW, I will have to disable the
timer interrupt close 5-20sec!!! This is the time it take for the
stage I control to move from one end to the other.
I hope my problem is clear!

Help is greatly appreciated!

Single board VME 800MHZ processor PC
no Xwindows, no Network, basically nothing but my program
Process is set as highest priority in user space.

Last edited by G35Coupe; 11-16-2004 at 02:05 AM.


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