The low frequency timer in GRTC will run off the LFCLK.
When the low frequency timer is started, the GRTC peripheral will automatically request the LFCLK source if the LFCLK is not already running.
The GRTC low frequency timer clock source can be selected using register CLKCFG.CLKSEL. The clock source cannot be changed after GRTC is started.
The clock source selection at GRTC is retained internally during System OFF mode, even though the CLKCFG.CLKSEL is reset on wakeup.
The SYSCOUNTER runs off the fast clock (16MHz clock), but uses only LFCLK while SYSCOUNTER is in sleep state.
See CLOCK for more information about clock sources.