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The ITS AMBA® AXI4 ACE-Lite master interface has a configurable width of 64 bits, 128 bits, or 256 bits. If the bypass switch is not included, the ID width is 4 bits, otherwise the ID width is one more than the ID width of the corresponding input channel.
The ACE-Lite master port issues accesses to the ITS private tables and Command queue. If the bypass switch is configured, the port also forwards transactions from the slave interface. The ACE-Lite bus can issue I/O coherent transactions, therefore you can place these tables in shared memory if required. Placing the Command queue in shared memory avoids having to flush the cache before executing ITS commands.
Arm recommends that if you place the ITS downstream of an ACE interconnect, then you must not place tables in shareable memory.
The ITS can issue the following transaction types:
ITS issued transactions output the DeviceID on the a<x>user_ signals. The DeviceID is used for information and does not have to be routed anywhere if it is not required. If the bypass switch is included, ITS issued transactions are identified by a value of 0 on a<x>id.
For more information, see Arm® GICv3 and GICv4 Software Overview.