Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Freescale Semiconductor/MK21D5WS/MCG/C7#0x0
OSCSEL=0
MCG Control 7 Register
MCG OSC Clock Select
0 (0): Selects System Oscillator (OSCCLK).
1 (1): Selects 32 kHz RTC Oscillator.
Reserved
no description available
https://github.com/cmsis-svd/cmsis-svd-data