How do I set up to use external crystal instead of internal RC

[ShiPC123]

Currently STM32G070 and STM32G030 are both internal RC oscillators, how do I set up to use the external 8Mhz crystal oscillator

[fpistm]

Hi @ShiPC123
I guess you use the generic target.
You can redefine default clock config like it is documented in the wiki:
https://github.com/stm32duino/Arduino_Core_STM32/wiki/Custom-definitions#systemclock_config

[ShiPC123]

hello I created a build_opt.h in the project. I changed the serial buffer size but the coding error was reported




How can I eliminate this error?

[fpistm]

Read carefully the wiki...
Build_opt.his a command line option not a real header. So do not include it...
And this is out of scope of this discussion about clock config.