How to set SYSCLKOUT for Beagle bone black ?

I am developing PWM driver for BBB in RTEMS RTOS. I need to set SYSCLKOUT for BBB. Can anyone suggest me what is the way to set up SYSCLKOUT ? or which specific register is responsible for that ?

SYSCLK is a fixed hardware clock which can’t be changed in software. What are you trying to do exactly?