2017-01-14 17:12 GMT+01:00 Jonathan Cameron <jic23@xxxxxxxxxx>:
> On 13/01/17 14:13, Matthias Klumpp wrote:
>> Hello!
>> I would like to use IIO for high-speed data acquisition. In order to
>> do that I implemented a new IIO driver for the ADC chip I am using
>> (MAX1133, maximum sampling frequency 200ksps).
>>
>> The initial approach with triggered buffers was way too slow,
>> achieving only a maximum sampling frequency of 4ksps.
> Any idea where the bottle neck was specifically? I'm guessing it
> might have been on the userspace side, but not certain.
The userspace side shouldn't be a problem, it is incredibly fast
(written to meet realtime deadlines even).
> [...]
>
> When you say use DMA, this part is an SPI device - so are you hand
> rolling DMA transfers from the spi controller?
>
> We've discussed in the past (long time ago now!) how to use spi
> controllers that support streaming modes but nothing has really come
> of it yet. What SPI controller are you using?
>
> Last time I was trying to do similar things (was a while ago now)
> I fairly quickly hit the limitation that the round trip time on SPI
> transfers even when using DMA was a lot longer than the theoretical.
> Any idea where you will be limited with that?
This is the problem - for each data acquisition, I make one spi_sync
call at time and I am really just hand-rolling SPI transfers from the
controller.
I think the gain in speed I saw came purely from the fact that I got
rid of the timer trigger, not so much from the DMA...
>> [...]
> Lars would indeed be the person I'd ask about this. I've cc'd
> him directly as often emails get buried in the list and missed
> by people for at least a little while.
>
> Keep us informed of how you get on. Will be useful info for others.
Thank you a lot for your reply and pointers! This project I am working
on started quite small and now became way bigger than expected, with
me touching a lot of areas I have less knowledge of, so any feedback
has tremendous value.
Kind regards,
Matthias
--
To unsubscribe from this list: send the line "unsubscribe linux-iio" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
