I use Kinetis K64. I use KSDK 2.2, and I configure the clock using online MCUXpresso clock conguration tool.
I wonder if I also have to call SystemCoreClockUpdate() and when since the variable SystemCoreClock is set by generated function BOARD_BootClockRUN().
You needn't to call the SystemCoreClockUpdate() function in you application. The function just update value of the SystemCoreClock variable that is also set in the BOARD_BootClockRUN() function (generated by the Clocks tool).
If you call the SystemCoreClockUpdate() (after BOARD_BootClockRUN()) the SystemCoreClock variable will not be changed (the same value shall be assigned to this variable).