Compile time GPIO pin number access.

[luqasz]

Hi.

Based on some board, I can have same pin functionality but on different pins. Board A has a FAN output on PC7, while board B on PC6 and so on. Since pin numbers are hardcoded as a struct field, how can I declare which pin to use ? E.g. a separate file which defines all pins based on some feature (feature would be a board name and revision) to use.

I'd like to avoid this situation:

    #[cfg(feature = "board_a")]
    let mut fan_pwm = gpioc.pc7.into_push_pull_output(&mut gpioc.crl);
    #[cfg(feature = "board_b")]
    let mut fan_pwm = gpioc.pc6.into_push_pull_output(&mut gpioc.crl);
    #[cfg(feature = "board_c")]
    let mut fan_pwm = gpioc.pc5.into_push_pull_output(&mut gpioc.crl);
    #[cfg(feature = "board_d")]
    let mut fan_pwm = gpioc.pc4.into_push_pull_output(&mut gpioc.crl);
    #[cfg(feature = "board_e")]
    let mut fan_pwm = gpioc.pc3.into_push_pull_output(&mut gpioc.crl);

This is simplified as it assumes all pins use GPIOC. Situation gets complicated when using different GPIO ports as well as CRH, CRL.

What I am used to (as I did some C/C++ embedded programming) and find most elegant solution:

#if defined(BOARD_A)
    using FAN_PIN = GPIO::PC7;
#elif defined(BOARD_B)
    using FAN_PIN = GPIO::PC6;
#else
    error "Board not implemented"
#endif

// Or include a hwconfig header file in which all ifdef's are.
#include "hwconfig.h"

int main() {
    fan = GPIO::PIN(FAN_PIN);
}

[burrbull]

All safety guaranties of GPIO API are based on idea that you can have only 1 pin instance each time.

Now it provided by collecting all pins in peripheral in 1 structure gpiox::Parts. Maybe there is some other way to provide it, I don't know.

You could try to partially decrease of cfg checks by manually restructuring of Parts. Something like:

    #[cfg(feature = "board_a")]
    let gpioc::Parts { pc7: fan_pwm, pcx: other_pin, crl: c_crl, crh: c_crh, .. } = gpioc;
    #[cfg(feature = "board_b")]
    let gpioc::Parts { pc6: fan_pwm, pcy: other_pin, crl: c_crl, crh: c_crh, .. } = gpioc;

    let mut fan_pwm = fan_pwm.into_push_pull_output(&mut c_crl);

or create some macro.

Alternatively we could make

stm32f1xx-hal/src/gpio.rs

Line 424 in c62c997

const fn new(mode: MODE) -> Self {

pub unsafe but I don't think this is good way to give user such gun.