On Thu, 4 Apr 2024 16:08:56 +0300 "Ceclan, Dumitru" <mitrutzceclan@xxxxxxxxx> wrote: > On 03/04/2024 18:22, David Lechner wrote: > > On Wed, Apr 3, 2024 at 2:50 AM Ceclan, Dumitru <mitrutzceclan@xxxxxxxxx> wrote: > >> On 02/04/2024 00:16, David Lechner wrote: > >>> On Mon, Apr 1, 2024 at 2:37 PM David Lechner <dlechner@xxxxxxxxxxxx> wrote: > >>>> On Mon, Apr 1, 2024 at 10:10 AM Dumitru Ceclan via B4 Relay > >>>> <devnull+dumitru.ceclan.analog.com@xxxxxxxxxx> wrote: > >>>>> From: Dumitru Ceclan <dumitru.ceclan@xxxxxxxxxx> > >>>>> > >> ... > >> > >>>>> properties: > >>>>> reg: > >>>>> + description: > >>>>> + Reg values 16-19 are only permitted for ad4111/ad4112 current channels. > >>>>> minimum: 0 > >>>>> - maximum: 15 > >>>>> + maximum: 19 > >>>> This looks wrong. Isn't reg describing the number of logical channels > >>>> (# of channel config registers)? > >>>> > >>>> After reviewing the driver, I see that > 16 is used as a way of > >>>> flagging current inputs, but still seems like the wrong way to do it. > >>>> See suggestion below. > >>>> > >>>>> diff-channels: > >>>>> + description: > >>>>> + For using current channels specify only the positive channel. > >>>>> + (IIN2+, IIN2−) -> diff-channels = <2 0> > >>>> I find this a bit confusing since 2 is already VIN2 and 0 is already > >>>> VIN0. I think it would make more sense to assign unique channel > >>>> numbers individually to the negative and positive current inputs. > >>>> Also, I think it makes sense to use the same numbers that the > >>>> registers in the datasheet use (8 - 11 for negative and 12 to 15 for > >>>> positive). > >>>> > >>>> So: (IIN2+, IIN2−) -> diff-channels = <13 10> > >>> Thinking about this a bit more... > >>> > >>> Since the current inputs have dedicated pins and aren't mix-and-match > >>> with multiple valid wiring configurations like the voltage inputs, do > >>> we even need to describe them in the devicetree? > >>> > >>> In the driver, the current channels would just be hard-coded like the > >>> temperature channel since there isn't any application-specific > >>> variation. > >> Sure, but we still need to offer the user a way to configure which > >> current inputs he wants and if they should use bipolar or unipolar coding. > > From the datasheet, it looks like only positive current input is > > allowed so I'm not sure bipolar applies here. But, yes, if there is > > some other variation in wiring or electrical signal that needs to be > > describe here, then it makes sense to allow a channel configuration > > node for it. > > AD4111 datasheet pg.29: > When the ADC is configured for bipolar operation, the output > code is offset binary with a negative full-scale voltage resulting > in a code of 000 … 000, a zero differential input voltage resulting in > a code of 100 … 000, and a positive full-scale input voltage > resulting in a code of 111 … 111. The output code for any > analog input voltage can be represented as > Code = 2^(N – 1) × ((V_IN × 0.1/V REF) + 1) > The output code for any input current is represented as > Code = 2^(N − 1) × ((I_IN × 50 Ω/V REF) + 1) > > I would say bipolar applies here, not a great idea because of the limitation on > the negative side (Input Current Range min:−0.5 max:+24 mA) so still, the option > is available. Just to check I am correct in thinking you 'might' use bipolar if you want to be able to measure small negative currents, but the range is much larger in the positive direction? J >
