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I have a Ubuntu Linux (4.6 kernel) running on a Zedboard, which is based on an ARM architecture. The architecture comes with a hardware module called Coresight, which enables HW-based program tracing. In my setup, the Coresight component is registered at physical address 0xf889c000. I want to configure the component through the device register etmcr, whose offset is 0x0. I tried to run devmem2 (a program helps manipulate physical memory via mmap) as a root to write some custom value to this register. The mmap threw no error, the write succeeded since the immediate readback value was the expected value. However, when I read this address again, the value didn't actually change. (Please see the attached screenshot). I've checked the Technical Manual of the Coresight and this register is for sure a RW register. So what could be the reason of what happened here? Why the register write succeeds but has no effect actually? Thanks in advance.