The SystemInit() function is defined in system_stm32l4xx.c. As I noted in Setting Up an Empty STM32CubeIDE Project :
Because the STM32L476 does include an FPU, I did include the file.
SystemCoreClockUpdate() simply updates the SystemCoreClock variable (also defined in system_stm32l4xx.c). For this example it’s not necessary, so I’ll edit my previous post to remove it.
I just used the default system clock configuration for this code.
Here’s a screenshot of my project explorer (click on it to view the entire image):
