STM32F412R HSI clock calibration with LSE

Hello,

I'm looking for a way to calibrate HSI by using LSE. I've found some documents that describes the way. My situation is a little bit tough. I can't change PCB and I can't draw a way from LSE to TIM5 - channel 4. I'm looking for a way which will allow me to connect LSE clock to a timer trigger input.

I appreciate any help,

Regards,

Ozgur