The AMBA interconnect has AXI and APB isolation blocks (AIBs) that are responsible for functionally isolating the AXI/APB master from the slave in preparation for an AXI/APB master or slave to be powered down. The AIB manages AXI and APB interfaces during the isolation process resulting in a graceful transition to a power-down state.
The AIB is transparent and offers zero latency during normal transactions. When isolation is commanded by the PMU, the AIB does not propagate new transactions; it will respond to the master with an SLVERR or ignore the transaction and cause the interconnect to timeout. The AIB response is selected by the lpd_slcr_aib.ISO_AIB{AXI, APB}_TYPE registers. When the isolation command is received, the AIB will allow all posted transactions to complete. When this is done, the AIB will assert an interrupt to indicate that the channel is quiescent and ready for an orderly isolation.