PwmOut initial value

Mbed OS
1

I’m suprised to find out that the PwmOut constructor does not have an initial value argument.

I have this use case where I want to keep an LED turned on during the transition from the bootloader to the application. Currently, since the PwmOut is initialized with 0 duty cycle, an annoying flicker is visible before the duty cycle is set to its correct value in the application.

I think this could be added to the PwmOut API in a non-breaking way with C++ default arguments. The question is how to implement this for all supported targets. Is it possible to indicate that an API is only available for some targets?

2

That’s an interesting use case!

Have you tried fixing the issue for your target as you suggested?

3

Yes, technically this is possible. Tested on an STM32 target.

At least it is possible to make it fast enough that it is not visible to my eyes :slight_smile:

4

then I suggest making a PR for mbed-core to review and discuss how to enable for other targets.

5

afaik the initial period time for the PwmOut is 20 ms, compatible with rc servos. That was already default for grandpa LPC1768 in mbed-OS2.
But a constructor with period and duty sounds good, it can be set to the old defaults when not provided.