The Cycle CouNT (CCNT) Register counts clock cycles.

The CCNT Register is:

To access the CCNT read or write CP15 with:

MRC p15, 0, <Rd>, c9, c13, 0 ; Read  CCNT Register

MCR p15, 0, <Rd>, c9, c13, 0 ; Write CCNT Register

The Cycle Count Register must be disabled before software can write to it. Any attempt by software to write to this register when enabled is Unpredictable.