On Monday 09 October 2006 10:10 am, Christopher "Monty" Montgomery wrote:
> >
> > You have not ** YET ** tried to do it the way that's known to work,
> > so it's no surprise you've been seeing the failures which lead to
> > the requirement to use double buffering.
>
> Uh... I've been trying to use the existing drivers for about 5 years.
> Never worked.
Never tried to do it the right way either, it seems, so that's not
in the least surprising. You're seeing two classes of problems:
- One of them is not using the API the way you should ... so
it's no wonder it "never" worked for you.
- Another is capacity limitations in one current implementation.
Both are fixable, but they're at different levels of the system.
> > From where I sit, I see your response as "I refuse to even consider
> > using that known-to-work solution, it's My Way Or the Highway."
>
> Tell me how a 4ms deep buffer will give me 2ms latency and I will eat
> my words. It's a promise.
Do you even understand what I mean when I talk about IRQ latency? It's
orthogonal to how deep your (double) buffering is. Adding deeper buffers
can't possibly give you IRQ latency guarantees.
To repeat for at least the third time, this is how it works: if
system IRQ latency is 2 msec, then you need at least 2msec data queued
AT ALL TIMES to make sure you don't get drop-outs. You get that by
double-buffering ... each buffer is 2 msec, so that when one of them
completes, the other can empty without causing dropouts. If you ever
get to the point where nothing is queued, you get drop-outs. Simple.
- Dave
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