Messages in this thread | | | Date | Thu, 2 May 2024 16:05:45 +0200 | Subject | Re: Supporting a Device with Switchable Current/Voltage Measurement | From | Peter Rosin <> |
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2024-05-02 at 15:49, Peter Rosin wrote: > Since you appear to need to change both the gpio pin and the io-channel, the > mux isn't a perfect fit. The closest you can get with the current code is to > create a gpio mux, I think. You would then use that mux twice to fan out both > io-channels, but only expose the "left leg" on the first fan-out and only the > "right leg" on the other. Something like this (untested, probably riddled with > errors, use salt etc etc): > > rcs: raw-current-sense { > compatible = "current-sense-shunt"; > io-channels = <&adc 0>; > io-channel-name = "raw-current"; > #io-channel-cells = <1>; > > shunt-resistor-micro-ohms = <3300000>; > }; > > rvs: raw-voltage-sense { > compatible = "voltage-divider"; > io-channels = <&adc 1>; > io-channel-name = "raw-voltage"; > #io-channel-cells = <1>; > > output-ohms = <22>; > full-ohms = <222>; > }; > > mux: gpio-mux { > compatible = "gpio-mux"; > #mux-control-cells = <0>; > > gpios-mux = <&main_gpio0 29 GPIO_ACTIVE_HIGH>; > }; > > current-sense { > compatible = "io-channel-mux"; > io-channels = <&rcs 0>; > io-channel-names = "parent"; > > mux-controls = <&mux>; > > channels = "current", ""; > }; > > voltage-sense { > compatible = "io-channel-mux"; > io-channels = <&rvs 0>; > io-channel-names = "parent"; > > mux-controls = <&mux>; > > channels = "", "voltage"; > }; > > What the mux solves is exclusion, so that the gpio pin is locked while > measurement is made on either current-sense or voltage-sense. > > However, the channels from the raw-{current,voltage}-sense nodes are exposed > to user space, and it will be possible to make "raw" measurements without > regard to how the gpio pin is set. That will of course not yield the desired > results, but is also a user error and might not be a big problem?
I just realized that it's also possible to do this "the other way around". Maybe that makes more sense?
Cheers, Peter
mux: gpio-mux { compatible = "gpio-mux"; #mux-control-cells = <0>;
gpios-mux = <&main_gpio0 29 GPIO_ACTIVE_HIGH>; };
rcs: raw-current-sense { compatible = "io-channel-mux"; io-channels = <&adc 0>; io-channel-names = "parent"; #io-channel-cells = <1>;
mux-controls = <&mux>;
channels = "raw-current", ""; };
rvs: raw-voltage-sense { compatible = "io-channel-mux"; io-channels = <&adc 1>; io-channel-names = "parent"; #io-channel-cells = <1>;
mux-controls = <&mux>;
channels = "", "raw-voltage"; };
current-sense { compatible = "current-sense-shunt"; io-channels = <&rcs 0>; io-channel-name = "current";
shunt-resistor-micro-ohms = <3300000>; };
voltage-sense { compatible = "voltage-divider"; io-channels = <&rvs 1>; io-channel-name = "voltage";
output-ohms = <22>; full-ohms = <222>; };
Cheers, Peter
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