Dear Otavio Salvador, > On Thu, Jul 18, 2013 at 12:31 AM, Marek Vasut <marex@xxxxxxx> wrote: > > Dear Otavio Salvador, > > > >> On Wed, Jul 17, 2013 at 4:12 PM, Jonathan Cameron <jic23@xxxxxxxxxx> wrote: > >> > Otavio Salvador <otavio@xxxxxxxxxxxxxxxx> wrote: > >> >>Hello, > >> >> > >> >>Mario and I are working at TI ADS124x driver and this chip can be used > >> >>in two ways: > >> >> > >> >>In case of ADS1247: > >> >> - 2 differential channels > >> >> - 3 single-ended channels > >> >> > >> >>In the first case it take two inputs and the chip returns the > >> >>difference between them; in the second case it does the same but you > >> >>must choose one channel to be the negative reference for all the other > >> >>inputs. This is how we understood the datasheet however the > >> >>single-ended use is quite confusing on it so we might be wrong. > >> >> > >> >>So we'd like to know the best way to handle those cases in the driver. > >> >> > >> >>One alternative we discussed is to use two attributes in the dts as: > >> >> ... > >> >> #channels = <2>; > >> >> channels = <0 3 > >> >> > >> >> 1 2>; > >> >> > >> >>So it'd take two channels. One composed by input 0 and input 3 and > >> >>another composed by input 1 and input 2. > >> >> > >> >>On the another case, we'd use: > >> >> ... > >> >> #channels = <3> > >> >> channels = <0 3 > >> >> > >> >> 1 3 > >> >> 2 3>; > >> >> > >> >>So it'd take three channels and all them comparing to input 3. > >> >> > >> >>Are we in the right route? Any hints how to better solve this? > >> >> > >> > Another option is to leave it entirely up to user space. See max1363 > >> > driver where both single ended and differential channels are supported > >> > at the same time with care taken in buffered mode. > >> > > >> > Not sure if that works for your case? > >> > >> I think it is nicer to have it set in the dt; we need the dt anyway so > >> it seems logical to get it setting the right channel. > > > > Can you please elaborate why is it logical? > > > > I took a brief look over the datasheet [1], here are the facts I see > > (correct me if I'm wrong). I first looked at Figure 51. : > > > > - ADS1246 has two input channels > > - ADS1247 has four input channels > > - ADS1428 has eight input channels > > > > - Each one of the 2/4/8 input channels can be connected to either P(+) or > > N(-) of the amplifier (figure 53) for the ADC. > > > > - Apparently, according to Figure 51. , it is possible to have only one P > > and one N channel enabled at time (and therefore sample only one pair of > > channels with the ADC) since the P and N rails are shared by all the > > inputs and there's only one ADC block. > > > > Therefore, the userland would have to export sysfs file for each of the > > channels where one would write if the channel is possitive(+) / > > negative(-) / not_connected(NC) and then trigger the start of sampling. > > > > What do you think? > > This does not make them act as differential against each other. > > We can have several combinations as: > > 0 - P / 1 - N (differential) > 0 - P / 1 - P / 2 - P / 3 - N (all differential to 3) > and so on. > > So how userland would tell which would be the differential to use? > > Our board has: > > 0 against 1 > 2 against 3 > > but it is a design choice. > > Am I missing something? echo 'P' > /sys/.../chan_mux_0 echo 'P' > /sys/.../chan_mux_2 echo 'N' > /sys/.../chan_mux_1 echo 'N' > /sys/.../chan_mux_3 Like this for example ;-) And this could be nicely implemented via IIO, but I believe there might even already be an IIO API for this stuff. Best regards, Marek Vasut -- 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
