2.1.4 I/O Home Node

The I/O Home Nodes (HN-I) are home-nodes for all CHI transactions that target AMBA slave devices. They act as proxies for all the RNs of the CCN-502, converting CHI transactions to ACE-Lite or AXI4 transactions.

They include support for the correct ordering of ARM device types and can optionally broadcast Data Synchronization Barriers (DSBs) and Data Memory Barriers (DMBs) into the slave I/O subsystem.

The HN-Is do not support coherent caching of any data read from or written to the downstream AMBA I/O slave subsystem. This means that any cacheable request sent to the HN-Is do not result in any snoops being sent to RN-Fs in the system, but are instead converted to the appropriate AXI read or write command and sent to the downstream AMBA subsystem. If an RN-F does cache data read from or written to the downstream AMBA I/O slave subsystem, coherency is not maintained, and any subsequent access to that data reads from or writes to the AMBA I/O slave subsystem directly, ignoring the cached data.

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