Creation of SAI pin tuple without I2SPinSdB

[JoseGuilhermeCR]

Hi there,

I'm trying to use the SAI peripheral on an H735... But I'm stuck as I don't have an SdB pin and using None on the tuple will lead to rustc E0282 and rustc E0283.

let sai1_pins = (
            mclk_a_pin.into_alternate(),
            sck_a_pin.into_alternate(),
            fs_a_pin.into_alternate(),
            sd_a_pin.into_alternate(),
            None
        );

The compiler says I should say what Option none belongs to... So I thought something like this would work, but now I've got another compiler error, rustc E0277.

let sai1_pins = (
            mclk_a_pin.into_alternate(),
            sck_a_pin.into_alternate(),
            fs_a_pin.into_alternate(),
            sd_a_pin.into_alternate(),
            None::<sai::i2s::I2SPinSdB<pac::SAI1>>
        );

The SAI example available in the examples directory uses SdB pin... but it's not shown anywhere how None should be used in the case you don't have this pin.

The log of the first error is as follows:

error[E0283]: type annotations needed
   --> src/pcm_4202_driver.rs:62:13
    |
62  |             None
    |             ^^^^ cannot infer type of the type parameter `T` declared on the enum `Option`
...
65  |         let mut sai1 = sai1.i2s_ch_a(
    |                             -------- type must be known at this point
    |
    = note: multiple `impl`s satisfying `_: sai::i2s::I2SPinSdB<stm32h7xx_hal::stm32::SAI1>` found in the `stm32h7xx_hal` crate:
            - impl sai::i2s::I2SPinSdB<stm32h7xx_hal::stm32::SAI1> for stm32h7xx_hal::gpio::Pin<'E', 3, stm32h7xx_hal::gpio::Alternate<6>>;
            - impl sai::i2s::I2SPinSdB<stm32h7xx_hal::stm32::SAI1> for stm32h7xx_hal::gpio::Pin<'F', 6, stm32h7xx_hal::gpio::Alternate<6>>;
    = note: required for `(stm32h7xx_hal::gpio::Pin<'E', 2, stm32h7xx_hal::gpio::Alternate<6>>, ..., ..., ..., ...)` to implement `sai::i2s::I2SPinsChA<stm32h7xx_hal::stm32::SAI1>`
    = note: the full type name has been written to 'target/thumbv7em-none-eabihf/debug/deps/tcc-9b1e8f6e0ab9f3e3.long-type-11402833594598164313.txt'
note: required by a bound in `i2s_ch_a`
   --> .cargo/registry/src/github.com-1ecc6299db9ec823/stm32h7xx-hal-0.13.1/src/sai/i2s.rs:359:15
    |
359 |         PINS: I2SPinsChA<Self>;
    |               ^^^^^^^^^^^^^^^^ required by this bound in `i2s_ch_a`
help: consider specifying the generic argument
    |
62  |             None::<T>
    |                 +++++

Now I'm definitely not an expert in the language, I've only used it for a few years now, but not professionally nor with this heavy usage of templates and etc... Am I missing something really stupid?

[JoseGuilhermeCR]

I got rid of the error by using None::<gpio::Pin<'E', 3, Alternate<6>>>, but it's definitely ugly... Still think there might be a way where I don't need to concern myself over the port/pin/mode of something I won't use.

[burrbull]

https://github.com/stm32-rs/stm32h7xx-hal/pull/431 does not change Sai interface, but also support pins in Default (Analog) mode to be passed in constructor. So this also should work:

let sai1_pins = (
    mclk_a_pin,
    sck_a_pin,
    fs_a_pin,
    sd_a_pin,
    None::<gpio::PE3>
);