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Driver Latency
Hello All:
I am working on a project which required writing a driver.
The hardware is an embedded VersaLogic PC-104 system (ISA bus).
The processor is a Pentium M, 1.6 GHz with 512 MB memory.
Operating system is Slackware 12.0 Linux with a 2.6.25.7 kernel compiled with the low latency preemptible kernel.
One of the system tasks involves operating a rotary knife device to size a product moving at 1,000 Ft. / Min. ( 200 In. / Sec). Our desired interrupt period for the driver is 62.5 uSec. generated by a counter / timer on one of the ISA I/O boards.
At times, the driver's clock interrupt may not run for >1.2 milliseconds. This doesn't happen very often and when it does happen, it has to happen at the wrong time to degrade our accuracy. But as all of you know, if it can happen, given enough time, it will happen.
Does anyone have experience with driver latency? Is this the normal latency for a non real-time Linux driver? Any suggestions for improvement?
Incidentally, running without X doesn't improve things. The latencytop utility apparently only works for user-land processes, so it didn't help.
As an aside, I have written a simulator to test the system using real-time Linux. The real-time Linux system is a 1.8 GHz Athlon that is happy running a 31.25 uSec period interrupt with ~ 15 uSec. max latency - roughly a 80x improvement.
Thanks
wevl
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