On 1 March 2016 16:02:00 GMT+00:00, Michael Welling <mwelling@xxxxxxxx> wrote: >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. Worse than that as you have to explicitly change the mux for each channel requiring an i2c write. > >> >> 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 -- Sent from my Android device with K-9 Mail. Please excuse my brevity. -- 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
