Hello Jack,
This pointer to function passes a delay function that will be executed after FLL is configured, this is done to make sure that FLL is stable after/during clock transition. If you do not want to execute any delay function, you can pass NULL pointer.
On the other hand, if you want to execute one delay function, you can use the CLOCK_FllStableDelay function as reference. This function waits for 1 ms aproximately.
static void CLOCK_FllStableDelay(void)
{
volatile uint32_t i = 30000U;
while (i--)
{
__NOP();
}
}
I hope this can help you!
Best Regards,
Isaac