The debug module is supported in three power domains. Refer to Table: JTAG and CoreSight Split Between Power Domains: JTAG and CoreSight Split Between Power Domains for more details. Whenever the DAP controller is available, the system is ready to debug the LPD; because the DAP is in the LPD. If the LPD is powered off, the DAP cannot be used.
A request needs to passed through the DAP (to the PMU_GLOBAL register) to power on the FPD and start an FPD debug.