On HSE values

[David-OConnor]

Is your feature request related to a problem? Please describe

What High-speed External oscillator (HSE) values are acceptable for use with Betaflight targets? Of note, when browsing unified configs, on a few I found the line set system_hse_mhz = 8, but this link implies this feature is deprecated for non-F4 targets. Most targets don't include one.

When using a generic unified target base (As described in the article about adding unified targets), how does this base know what HSE value to use? Choosing one lower in software than what your board uses will likely result in an overclock and immediate crash. Does BF default to HSI until you specify it?

Does BF assume all boards use HSE = 8Mhz?

Describe the solution you'd like

A description of how BetaFlight unified targets select the HSE value, or if they default to HSI until one is specified in a config.

Describe alternatives you've considered

N/A

Other information

I'm troubleshooting a board not working with BF, and am treating this is a possible cause.

This is a support question per the template, but I've been unable to find an answer on the specified channels.

[haslinghuis]

https://programming.vip/docs/stm32-development-explanation-of-clock-system.html
https://community.st.com/s/question/0D50X0000BYoP9mSQF/which-clock-source-to-use-hsi-or-hse

[David-OConnor]

Thank you for the links. This question is regarding Betaflight behavior specifically.

[haslinghuis]

Not sure about the comment about why the cli setting would be F4 only as I see SPRacing and some NUCLEO targets are using HSE_VALUE using the target.mk,

Some targets are defining HSE_VALUE but it is set globally in the Makefile in the case it was not defined before anyway.

# default xtal value for F4 targets
HSE_VALUE       ?= 8000000