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You can use the P-Channel to isolate a chip from the system.
The P-Channel has three states:
0x0). This is the normal functional mode.
0x9). In this state, the GIC does not send any cross-chip messages. It accepts incoming messages but does not process them.
0xF). In this state, the GIC does not send any cross-chip messages and does not accept any incoming messages. The icrdtready signal is clamped LOW to prevent accesses entering the GIC.
While in both the CONFIG and OFF states, register accesses that are normally sent to another chip are serviced locally. Therefore, the Routing table registers read the local versions instead of the copies of the Routing table owner. The same is true for SPIs that are owned remotely. Therefore, it is safe to save and restore the Distributor register values in either of these P-Channel states.
You can exit reset in either RUN or OFF states by setting the initial value of the pstate signal. If you have saved register values and intend to restore them, you must use the OFF state and restore the Routing table first before attempting to restore any SPI registers.