On Thu, 18 Jul 2013 14:59:34 +0000 Mario Domenech Goulart <mario@xxxxxxxxxxxxxxxx> wrote: > On Thu, 18 Jul 2013 15:54:03 +0200 Lars-Peter Clausen <lars@xxxxxxxxxx> wrote: > >> On 07/18/2013 02:02 PM, Otavio Salvador wrote: >>> On Thu, Jul 18, 2013 at 2:50 AM, Lars-Peter Clausen <lars@xxxxxxxxxx> wrote: >>>> >>>> Well the standard API as Jonathan said is to expose all possible pin >>>> combinations. In this case that might be up to 8x8=64 channels. In my >>>> opinion that's fine, but on a specific board maybe not all combinations are >>>> valid. So you might want to specify in your platform data or devicetree that >>>> only a subset of these 64 channels is valid and should be exposed to >>>> userspace. In my opinion it makes the most sense to handle this in the IIO >>>> core since this is a generic requirement, nothing specific to this chip. >>>> E.g. even for 'simple' converters you'll find situations where some pins >>>> might not be connected. >>> >>> Right and how should we do this? >>> >>> Because it would not be 8x8 but it has also the single-ended >>> combinations (using different N inputs). >> >> Does the device really support single ended, it looks to me as if it only >> supports pseudo-differential configurations. > > That's not very clear to me either. The datasheet states the chips have > single-ended inputs, but the mux configuration always assume a positive > input and a negative input. > > I'm assuming the "single-ended" mode refers to using an arbitrary input > as negative reference to all the other n-1 inputs. I suppose that'd be > a pseudo-differential configuration, right? Here's part of a message from a TI employee that explains the single-ended mode: "The ADS1248 has 8 multiplexed inputs. When we describe a single ended input, we use one input as a common line, and use the remaining 7 inputs measured against common. In this way we decribe this each as a single ended input. That's how we get 7 single ended inputs." Quoted from http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/p/31638/110153.aspx#110153 Best wishes. Mario -- 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
