Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/NXP Semiconductors/LPC5410x/SYSCON/MAINCLKSELA#0x0
SEL=IRC_OSCILLATOR
Main clock source select A
Clock source for main clock source selector A
0 (IRC_OSCILLATOR): IRC Oscillator
1 (CLKIN): CLKIN
2 (WATCHDOG_OSCILLATOR): Watchdog oscillator
3 (RESERVED): Reserved
Reserved
https://github.com/cmsis-svd/cmsis-svd-data