4.1.19. 764319: Read Accesses to DBGPRSR and DBGPRCR May Generate an Unexpected UNDEF
CP14 read accesses to the Device Power-down and Reset Status (DBGPRSR) and Device Powerdown and Reset Control (DBGPRCR) registers generate an unexpected UNDEFINED exception when the DBGSWENABLE bit, bit in the Coresight Components APB-AP Control/Status Word (CSW) register at offset 0x00, is 0, even when the CP14 accesses are performed from a privileged mode.
Because of this erratum, the Device Power-down and Reset Status (DBGPRSR) and the Device Powerdown and Reset Control (DBGPRCR) registers are not accessible when DBGSWENABLE=0.
This erratum is unlikely to cause any significant issue in Cortex* -A9 based systems because these accesses are mainly intended to be used as part of debug over power-down sequences, and the Cortex* -A9 does not support this feature.
The workaround for this erratum is to temporarily set the DBGSWENABLE bit to 1 so that the DBGPRSR and DBGPRCR registers can be accessed as expected. There is no other workaround for this erratum.