On 02/07/2013 17:21, Lars-Peter Clausen wrote: >>> >>> I was looking at that yesterday as I had to had a scale for the >>> temperature sensors. You'll have to be careful because the maximum >>> measured voltage when DIVIDE_BY_TWO is not set is 1.85V and when it is >>> set, it becomes VDDIO - 50mv. > > I had a quick peak at the datasheet and I think that's a typo. VDDIO is 3.3V. > This sentence also doesn't make much sense if divide by two would actually > lower the range. "For input channels (other than BATT, 5V, or VDDIO) with > signals larger than 1.85 V, the divide-by-two option should be set." > Yeah, what I think they meant is if !DIVIDE_BY_TWO : Vmax = 1.85V else Vmax = 3.25V. So it may not be as easy as multiplying hte scale by two. I couldn't test it, so I didn't implement it. >>> >>> Also, scaling for quite a lot of channels is fixed. You'll also get >>> channels with a fixed divider that can take DIVIDE_BY_TWO. That is quite >>> a mess ;) >> >> Thank you, I checked and it's easy to add custom sysfs attributes using >> IIO_DEVICE_ATTR(). I was thinking whether adding a divide_by_two attribute per >> channel: >> >> divide_by_two0 >> divide_by_two1 >> ... >> divide_by_two7 >> >> or a unique divide_by_two descriptor that admits a mask value for all channels. >> I think the first approach (one per channel) is cleaner. Opinions? > > Just use the scale attribute for this. That's the standard way to handle this, > don't invent custom interfaces if there is already a generic one. > Hector, you can have a look at what I did there: http://marc.info/?l=linux-iio&m=137269905605960&w=2 Add IIO_CHAN_INFO_SCALE to .info_mask_separate in the MXS_ADC_CHAN macro. Then, implement the scaling in the switch case in mxs_lradc_read_raw and you'll probably also want to implement a write_raw. -- Alexandre Belloni, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com -- 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
