[LAD] MIDI jitter - was: automation on Linux (modular approach)

[David Olofson]

On Thursday 25 March 2010, at 12.49.31, Ralf Mardorf <ralf.mardorf at alice-
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...?


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//David Olofson - Developer, Artist, Open Source Advocate

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