David Olofson wrote:
> On Thursday 25 March 2010, at 12.49.31, Ralf Mardorf <ralf.mardorf@email-addr-hidden-
> dsl.net> wrote:
> [...]
>
>> Btw. the
>> graphics has access to the main memory, unfortunately it's a shared RAM,
>> OTOH I used HPET so unwanted interrupts because of a shared RAM
>> shouldn't be the cause, if I do understand the workings of HR timers
>> correctly.
>>
>
> Interrupts can't save you if bus-master DMA is blocking the CPU's access to
> RAM. Whatever IRQ source and kernel interrupt handling code you're using has
> no bearing on this. If the interrupts are generated by external or internal
> (to the CPU) timers shouldn't matter either. (Even if external IRQs are
> delayed while the bus is busy, it doesn't make a difference, as the CPU can't
> respond until the bus is free anyway.)
>
> Either way, I don't think that should be a problem, as busmaster DMA is
> normally done in short bursts, rather than large blocks. Unless you're pushing
> the limits of RT-Linux or RTAI, it should affect nothing but bandwidth from a
> practical POV. Then again, perhaps not all hardware is that well behaved...?
>
Thank you for the information. At least when doing test I guess the
limits are untouched.
Ralf
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Received on Thu Mar 25 16:15:02 2010
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