We observed that when we enter EM1 then SysTick timer (being configured at 1ms interrupt) wakes controller from EM1 every 1 ms. As per our understanding in EM1 HFCORECLK_CM3 is disbaled and SysTick timer is fed from it (not configured with RTC).
Please let me know what is I am missing in understanding it.
P.S. We disable SysTick before entering EM1 and other interrupts wake MCU form it and when the work is done we configure back SysTick timer and enter EM2 until the cycle completes.
In EM1 the HFCORECLK_CM3 itself is not turned off, but the sub-branch that goes to the CPU is turned off. The SysTick is also in the CM3, but this clock continues to run in EM1.
Okay. Thanks for explaining it.