STM32H7S78 DK switch HSE clock problem

[OKesk.1]

I am trying LTDC color keying application. LTDC uses HSI as clock source. I want to make all system clock HSE. Then I will be able to use PLL3 with HSE. However, the processor example I am using uses an external ram with boot_xip. All clock settings in boot_xip are made for HSI.

Whenever I want to make system clock HSE, RCC_CKPROTR_XSPICKP 1 comes when application starts. This prevents me from making HSE ON. When I close manually, even if HSE is ON, the software crashes when RCC_CFGR_SW changes.

My crystal works fine. I tested it with RCC ClockConfig example. However, the example does not include a boot software and application. Therefore, how can I change the system clock configuration in Application?