On 08/18/2011 12:18 PM, Jonathan Cameron wrote:
Hi All, Whilst working on some of the capacitance adc drivers yesterday I added a second differential type. Whilst we only had IIO_VOlTAGE_DIFF, it seemed easier to handle it as a special case - now we have IIO_CAPACITANCE_DIFF, I'm not so sure.
IIO_CURRENT_DIFF is also likely to be added in future...
The alternative is to add another flag to struct iio_chan_spec and build the differential names automatically (easy enough I think). Nastier is how to handle the related event codes. As we haven't pushed out the new 64 bit codes, this is a perfect time to slip in a change there (rather than two changes back to back.) Current macro to generate codes is: define IIO_EVENT_CODE(chan_type, modifier, direction, \ type, chan, chan1, chan2) \ (((u64)type<< 56) | ((u64)direction<< 48) | ((u64)modifier<< 40) | \ ((u64)chan_type<< 32) | (chan2<< 16) | chan1 | chan) So if we were to steal a bit to mark channels as differential, where would we do it? Obvious choice is in type - reducing max number of types to 128 - can't see that being a problem any time soon. Could pinch the top bit off direction instead - that one has way more values than I can think of uses for...
In the way we use chan_type today - I think it would be the best spot.
This is going to be an annoyingly invasive patch to do. I'll probably scrap the use of the IIO_CHAN macro for all differential channels rather than adding another parameter to it. Plan was to scrap that macro entirely eventually, so not such a bad thing. Jonathan
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