Re: Mixing AD conversion and DIO writes

Hi again,

Let me ask the question a different way - How can I check if a command
that was launched with a finite set of scans is done ?

Thanks
Daniel

On Sat, Mar 12, 2005 at 10:15:36PM -0500, Daniel Nilsson wrote:
> Hi,
> 
> I'm looking for some advice for how to best achieve some sampling
> requirements using Comedi. I'm using a card, NI AT-MIO-16E-10, which
> is rather old but should be OK for my purpose. This card supports
> 100kS/sec and has a 12bit AD converter.
> 
> I need to do both AD conversions on 4 channels as well as toggle some
> digital I/O lines every so often. Ideally, the digital I/O lines needs
> to be toggled every few hundred milliseconds but it's not that time
> critical. The digital I/Os are used to keep a watchdog alive on a
> connected board. I also need to sample data on 4 channels (all with
> potentially different ranges) and then run those samples through a
> filter. I don't need continous sampling though, but while sampling I'd
> like to sample rather quickly so that I don't get aliased noise. I
> also can't toggle the digital I/O lines while sampling, noise from the
> digital I/O lines will distort the AD conversions.
> 
> So what I was looking to do was something like this:
> 
> Sample on 4 channels _at_ 25kS/sec each = 100kS/sec total.
> 
> If I sample 20000 samples total that should should take about 250ms or
> so, and should give me 5000 samples per channel. Assuming each sample
> is 2 bytes, this should also fit in the default buffer which at least
> for my card seems to be 64kB. After taking the 20000 samples I can
> process this data, run it through the filter etc, as well as toggle
> the digial I/O line and then start the process over again.
> 
> Question is, should I use a command to do this ? Does this mean I need
> to start a command that makes 5000 scans and then stops or is there a
> better way ? How can I check if the command is done without relying on
> counting the number of bytes that I can read() from the device (what
> happens if there is an error ?). Any thought/ideas are welcome !
> 
> Thanks
> -- 
> Daniel Nilsson
>  
> 

-- 
Daniel Nilsson

Received on 2005-03-16Z01:23:30