64.5.4.2.1 Debug Interface Access Prevention

The SECUMOD can be used to block access to the system through the Arm processor's Debug Access Port interface. This feature is implemented via SECUMOD_JTAGCR, which enables assertion of the nDBGRESET reset input of the debug interface. Writing a ‘1’ to SECUMOD_JTAGCR.FNTRST prevents any activity on the TAP (Test Access Port) controller.

On standard devices, FNTRST resets to ‘0’ and thus does not prevent debug access.

FNTRST also locks the boundary scan when set.