Vybrid contain A5 with ETM from ARM so it is really ARM question. Nevertheless in ARM Information Center in CoreSight ETM-A5 Technical Reference Manual in chapter 2.3.1. Clock signals is written "This must be the same clock as that wired to the CLKIN input of the Cortex-A5 processor." So we can say that timestamp is clocked by Vybrid A5 clock not platform clock.
Vybrid contain A5 with ETM from ARM so it is really ARM question. Nevertheless in ARM Information Center in CoreSight ETM-A5 Technical Reference Manual in chapter 2.3.1. Clock signals is written "This must be the same clock as that wired to the CLKIN input of the Cortex-A5 processor." So we can say that timestamp is clocked by Vybrid A5 clock not platform clock.