Paolo Mantegazza wrote:
>
> There is no timer reading in periodic mode. You are right when you say
> that the jitter is depending on system activity. In fact you are causing
> more interrupts and, even if it is true that Linux interrupt are
> deferred processing, they must be at least acknowledged. Nonetheless the
> jitter they cause is not enough to justify the highest peaks.
>
> However there is no chance to get the details of what is causing what:
> bus contention, DMA steals, cache disruption all cooperate to the mess.
>
> Note that the jitter is almost independet from the CPU clock. I also got
> the idea that having a timer on the PCI bus does not make any
> difference, the related interrupt will be signalled by the 8259 PIC
> anyhow.
>
> I always thought that if absolutely much less than 20 us jitter is
> needed you need something different from a general purpose computer.
> That is what DSPs were born for.
>
> Ciao, Paolo.
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Hi, I'm studing the timing behavior of RealTime Linux and I think that kind of
discutions are very interesting.
Where can I get more info about bus contention and DMA cycle steals. I dont know
anythink about the PCI bus. I post a message in this group a time ago about a PCI
spec. but I only had a link to the PCI Expert Group ??? homepage (not online,
I have to pay......)
Another question, do the Pentium architecture have an EISA bus on the system,
besides the PCI bus? If I write to the parallel port, for instance, the system
uses the PCI bus? Sorry my "naife" questions :)
Thanx
sorry my bad english
Pedro Martins
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