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Cortex-A7 Generic Timer Clock and Operation

Sajjad Ahmed

Hi,

     I'm using NXP imx6ul-evk(single core cortex-a7 processor) and I'm trying to operate CPU at different frequencies(642MHz, 480MHz, 100MHz, 12MHz) and experiencing time drift on certain frequencies (Generic Timer's time lags Real Time), I'm using virtual timer.  I've certain confusions which are following:

* Which clock is going to Generic timer,Why it has range, as I read it operates in range [1-50 MHz], if so then what is its relation with system's core clock which has range up to 696 MHz?

* On system side I've three memory mapped system_counter block (SYSTEM_COUNTER_CTRL = CNTControlBase), SYSTEM_COUNTER_CMP and (SYSTEM_COUNTER_RD = CNTReadBase). 

* I consider the timer clock rate 8000000 Hz, load 80000 in CNTV_TVAL and it gives me 10 ms interval but changing the system frequency cause time drift?

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