The purpose of the Cycle CouNT (CCNT) Register is to count the number of clock cycles since the register was reset. See bit  of the c9, Performance Monitor Control Register.
The CCNT Register is:
a read/write register common to Secure and Nonsecure states
accessible as determined by c9, User Enable Register.
Table 3.94 shows the results of attempted access for each mode.
 An entry of Undefined in the table means that the access gives an Undefined Instruction exception when the coprocessor instruction is executed.
To access the CCNT Register, 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 CCNT Register must be disabled before software can write to it. Any attempt by software to write to this register when enabled is Unpredictable.