WithPwm trait should be public

[Fomys]

I writing a generic struct that takes a pwm channel to control a motor.

We've tried this code:

struct Motor<TIM: TimerExt, const C: u8> {
    pwm: PwmChannel<TIM, C>,
}

And I get the following error:

error[E0599]: the method `get_max_duty` exists for struct `PwmChannel<TIM, C>`, but its trait bounds were not satisfied
  --> base-roulante/src/main.rs:64:73
   |
64 |         let consigne = pid_correction / Self::MAX_CORRECTION * self.pwm.get_max_duty();
   |                                                                         ^^^^^^^^^^^^ method cannot be called on `PwmChannel<TIM, C>` due to unsatisfied trait bounds
   |
  ::: /home/fomys/.cargo/registry/src/github.com-1ecc6299db9ec823/stm32f1xx-hal-0.9.0/src/timer/pwm.rs:89:1
   |
89 | pub struct PwmChannel<TIM, const C: u8> {
   | --------------------------------------- doesn't satisfy `PwmChannel<TIM, C>: PwmPin`
   |
   = note: the following trait bounds were not satisfied:
           `TIM: stm32f1xx_hal::timer::sealed::WithPwm`
           `TIM: stm32f1xx_hal::timer::sealed::WithPwm`
           which is required by `PwmChannel<TIM, C>: PwmPin`

The ideal resolution would be to add trait bound with WithPwm trait, but it's impossible as it's a sealed trait.

Shouldn't it be public in order write this trait bound ? If this isn't the case, how should I resolve ?

[burrbull]

Yeah. Generic code with sealed trait is often problematic.
As fast fix you could use get_max_duty from PwmPin:

stm32f1xx-hal/src/timer/hal_02.rs

Line 136 in f9b24f4

impl<TIM: Instance + WithPwm, const C: u8> embedded_hal::PwmPin for PwmChannel<TIM, C> {

[Fomys]

To use PwmPin I have to add the trait bound PwmPin<Duty = u16> as the Duty is also generic.
Should I make a PR to make WithPwm public ?

[Tnze]

I think we should move methods from Pwm and PwmHz to a new trait. Thus we can wrap PWMs in struct without writing trait bound of the TIM (which is impossible because TIM requires WithPwm which is sealed).

trait PWM {
    fn enable() ...
    fn disable()....
    fn get_duty()....
    ....
}

impl<TIM, REMAP, P, PINS> PWM for PwmHz<TIM, REMAP, P, PINS> where ... {
...
}

impl<TIM, REMAP, P, PINS> PWM for Pwm<TIM, REMAP, P, PINS> where ... {
....
}