init without a RST pin

[MathyV]

Hi,

I almost feel stupid having to ask this but I can't seem to figure it out on my own: I have a device where the ST7789 doesn't have a separate RST pin, it is connected to the RST pin of the ESP32. I got it working with the driver, which is great, but I can't seem to run the init function without passing a real Pin to it.

Obviously I don't want to use a fake pin, in the first place not because there are actually no free pins left on the device so I can't use other functionality.

In one of the examples it says None::<OutputPin>, which doesn't work. I also tried with None::<AnyOutputPin> and many other variants but it always comes down to either errors that the size isn't known at compile time and/or the trait embedded_hal::digital::v1::OutputPin is not implemented.

Could it be related to the v1 vs v2 implementation of digital io in embedded-hal vs esp-idf-hal? Or am just being stupid and am I failing to see the obvious here? Either way I'd appreciate your input :rofl:

Thx, Mathy

[almindor]

In one of the examples it says None::<OutputPin>, which doesn't work. I also tried with None::<AnyOutputPin> and many other variants but it always comes down to either errors that the size isn't known at compile time and/or the trait embedded_hal::digital::v1::OutputPin is not implemented.

I believe this has to be a bug, as you need "some type" unless we use the ! notype but that is unstable.

So the easiest way to do this will be to implement OutputPin over a newtype that does nothing.

Something like:

struct NoPin;

impl embedded_hal::digital::v2::OutputPin for NoPin {
    type Error = ();

    fn set_high(&mut self) -> Result<(), Self::Error> {
        Ok(())
    }

    fn set_low(&mut self) -> Result<(), Self::Error> {
        Ok(())
    }
}

followed by builder.init(&mut delay, None::NoPin);

This is a good case of missing ergonomics (and a bug in the docs/examples). I wonder if a NoPin should be provided by the embedded-hal directly though.

[yanshay]

I used this solution and it worked for the example provided in this crate. However when I tried with more complex application I had a compilation error that required me to replace Error = () with Error = Infallible . Not sure why, but it worked :-) Maybe it has to do with me using embedded_hal::digital::v2::OutputPin (v2, not v1)

Also, it should be builder.init(&mut delay, None::<NoPin>);

struct NoPin;

impl embedded_hal::digital::v2::OutputPin for NoPin {
    type Error = Infallible;

    fn set_high(&mut self) -> Result<(), Self::Error> {
        Ok(())
    }

    fn set_low(&mut self) -> Result<(), Self::Error> {
        Ok(())
    }
}

[rfuest]

If we decide to merge #81 it will be easier to use displays without a connected reset pin, because the reset pin it is no longer a init parameter. And a noop implementation of the OutputPin trait is already included in the create.

[yanshay]

And a noop implementation of the OutputPin trait is already included in the create

In the create or in the crate? If in the crate, where is it? I couldn't find one.

[rfuest]

And a noop implementation of the OutputPin trait is already included in the create

In the create or in the crate? If in the crate, where is it? I couldn't find one.

Sorry, that part of my comment was a bit confusing. I meant crate (create was a typo), but only after #81 gets merged.

[sampaioletti]

specific to esp, if you dont want to create a new type it is implemented for Pin driver, just pick an arbitrary pin.

None::<esp_idf_hal::gpio::PinDriver<esp_idf_hal::gpio::Gpio18, esp_idf_hal::gpio::Output>>

[almindor]

The pin is now handled by Builder::reset_pin. To initialize without it just omit this call in your builder routine.