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The HN-Is support exclusive access on ReadNoSnp and WriteNoSnp transactions to any address that maps to an HN-I.
Each HN-I includes 16 system monitors as defined in the CHI architecture for tracking of these transaction types. Only 16 unique logical threads, either processor or device threads, designated by a unique combination of SrcID and LPID, can concurrently access the HN-I system exclusive monitors.
If 16 unique threads are allocated a monitor with a ReadNoSnp exclusive to an HN-I, and those monitors have not yet been deallocated by a subsequent WriteNoSnp exclusive, then if another unique thread tries to allocate a monitor with a ReadNoSnp exclusive transaction, that transaction completes with an indication that the monitor was not successfully allocated. This prevents that thread from making forward progress in completing its exclusive access.
All exclusives targeting an HN-I are terminated at the HN-I and are not propagated downstream, regardless of the value of the HN-I PoS Control register and Auxiliary Control register.