I measure software execution time on A53 using XTime_GetTime() in xtime_l.h. What is the unit of this counter value?
XTime_GetTime() gets the counter value from the Physical Counter (CNTPCT_EL0) in A53. It works at the APU clock frequency.
This logic generates a tick after N clock pulses, where N is as follows:
N=(1/2 APU clock frequency)/100 MHz
100 MHz is a configurable clock that goes to the system timestamp generator in IOU.
Normally it is 100 MHz after boot but it can be changed using the crl_apb register (Address: 0xFF5E0128).