Are the app_timers using 32 768 Hz RTC?

Question

Two questions: 
 
 
 If I use Nordic's library functions such as app_timer_create() and app_timer_start(), are the timers using the low-power RTC timer running with the 32 768 Hz crystal? Our board has that crystal installed, of course. Or do they just utilize the timers running with CPU clock (16 MHz)? 
 
 
 What is the simplest way to read milliseconds elapsed since the system started running? 16 bits would be enough, so it doesn't matter if it wraps around back to zero.

Eric Stutzenberger · Accepted Answer

Hi Jarmo, 
 Yes, the app_timer library uses RTC_1 for its operations. It has roughly 1 ms resolution. 
 If you don't need app_timer, then one easy way to count ticks would be to manually setup RTC_1 to fire an interrupt using a capture compare register. You can set this up for roughly 1 millisecond intervals. Then in the interrupt, you can simply increment a tick counter and then exit the interrupt. You could then use this value for timing. 
 If you don't actually need the tick count and instead need to execute tasks at certain intervals, you can use the app_timer library. Note that app_timer events occur in an interrupt context (SWI_0 I think). If you are accessing other resources you may want to use a flag to trigger the main loop to run the event handling instead. 
 Hope this helps, 
 Eric

Are the app_timers using 32 768 Hz RTC?

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