External access permission to the PMU registers is subject to the conditions at the time of the access. Table 12.1 describes the processor response to accesses through the external debug and memory-mapped interfaces.
|Off||EDPRSR.PU is 0||
Processor power domain is completely off, or in a low-power state where the processor power domain registers cannot be accessed.
|DLK||EDPRSR.DLK is 1||OS Double Lock is locked.|
|OSLK||OSLSR_EL1.OSLK is 1||OS Lock is locked.|
||External performance monitors access is disabled. When an error is returned because of an EPMAD condition code, and this is the highest priority error condition, EDPRSR.SPMAD is set to 1. Otherwise SPMAD is unchanged.|
|SLK||Memory-mapped interface only||Software lock is locked. For the external debug interface, ignore this column.|
|Default||-||None of the conditions apply, normal access.|
Table 12.2 shows an example of external register condition codes for access to a performance monitor register. To determine the access permission for the register, scan the columns from left to right. Stop at the first column whose condition is true, the entry gives the register access permission and scanning stops.