[reformatted and edited to get rid of the top posting]
On Tue, 28 Jul 2009, tseredynski wrote:
> --- In Jim Jackson <> wrote:
>> On Mon, 27 Jul 2009, tseredynski wrote:
>>
>>> Hm... could you tell me about how much more accurate the rate would be if
>>> I used the kernel driver? I switched the the T4 timer, and now poll it
>>> as it counts up until it is greater than a certain value (this way it
>>> catches the value for sure, though maybe not exactly on but close). I am
>>> aiming for a rate of 1kHz, and I get a value that ranges from about
>>> 950-1000Hz. It no longer gets the large drops in sample frequency that I
>>> got when trying with T3, but I'm still curious if this is as accurate as
>>> I can get or whether using a kernel driver would enable me to achieve
>>> something like a 995-1000Hz range.
>>
>> Phil's driver can sample at 8KHz, and it is good enough for sound sampling.
>> Subjectivey this would imply the timer accuracy far better than your user
>> land code.
>>
> Do you mean it's better because it can sample at a higher rate? So can
> mine, but I need mine to sample exactly at 1kHz, so I have it reduced. Or
> did you mean that his can sample exactly at 8000Hz? With no +/- variance
> in the sample rate?
OK, I was assuming too much. Jitter in the sampling rate of the amount you
quote for you application, would be very noticable in sound sampling.
Given that Phil's kernel driver can be used ok for sound sampling and at
the higher rate (hewnce load on the hardware) implies a better performance.
I recommend you do some more research on this stuff.
Have you checked your application performance with other applications
running? An ISR based kernel solution will be a lot more
robust. Linux is not a realtime OS and expecting this sort of accuracy in
userland is often wishfull thinking.
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