When programming the ETM registers you must enable all the changes at the same time. For example, if the counter is reprogrammed, it might start to count based on incorrect events, before the trigger condition has been correctly set up.
You can use the ETM programming bit in the ETM Control Register to disable all trace operations during programming. To do this follow the procedure shown in Figure 3.1.
The individual registers are not described here. For more information, see the ETM Architecture Specification.
The processor does not need to be in the debug state while the ETM registers are being programmed.