On Tue, Mar 01, 2016 at 08:35:01AM +0000, jic23@xxxxxxxxxxxxxxxxxxxxx wrote: > On 01.03.2016 02:42, Michael Welling wrote: > >On Mon, Feb 29, 2016 at 10:09:10PM -0300, Lucas De Marchi wrote: > >>On Mon, Feb 29, 2016 at 9:50 PM, Michael Welling <mwelling@xxxxxxxx> > >>wrote: > >>> On Fri, Feb 05, 2016 at 03:17:18PM +0200, Daniel Baluta wrote: > >>>> The driver has sysfs readings with runtime PM support for power saving. > >>>> It also offers buffer support that can be used together with IIO software > >>>> triggers. > >>>> > >>> > >>> Daniel, > >>> > >>> So I noticed something yesterday while testing new boards. > >>> The channels are occassionally swapping when accessing data from multiple channels. > >>> > >>> I wrote a simple bash script to demonstrate. > >> > >>This happened to me in a previous version of the patch. I remember it > >>being fixed in the last version (or at least I could not reproduce). > >>I'll test again tomorrow with your script. > >> > > > >Here is what I believe is happening. > > > >The request for a conversion on a new channel comes in while the > >conversion > >for the previous channel is still converting. The driver waits > >approximately > >one conversion cycle. The previous channel completes within this timeframe > >and the MUX is changed and the new sample is started. The new sample is > >still > >converting and the driver returns the value from the previous conversion. > > > >For a test I multiplied the conv_time value by 2 in the > >ads1015_get_adc_result > >function. This allows time for the current sample flush out and always > >returns > >the appropriate channel's value. > > > >Looking at the buffered mode it appears that only one channel is being > >accessed > >at any time. This being the first one in the active_scan_mask found by > >find_first_bit. So the MUX would never change is buffered mode as far I > >can > >tell. > > > >Don't we typically want to read all of enabled channels in buffered mode? > In some devices that is effectively impossible (fifo's that fill only from > the currently > selected channel). That is what the onehot validation callback is about. > In this particular case it looks like doing a multichannel read is fair bit > more time > consuming than a single channel read and so will result in a considerable > reduction in > throughput. This is of course why many parts include a simple sequencer! Yes the sampling rate would effectively be divided by the number of channels enabled. > > Anyhow, supporting multi channel buffered reads could be done (probably) but > you > would want to fall back to the single channel case as it is now. Understood. > > Jonathan > >>Lucas De Marchi > >-- > >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 -- 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
