2.11.2. Regulation based on outstanding transactions

The CCI-400 offers an additional mechanism for regulating traffic flows for the benefit of overall performance. Each ACE-Lite slave interface has an optional, programmable, mechanism for limiting the number of outstanding read and write transactions, where an outstanding transaction is a read request without read data, or a write request without a response.

If you enable regulation, the following programmable values set the permitted number of outstanding transactions:

You can use these parts to set a fractional number of outstanding transactions, for example, 2.75.

You can program each interface individually, and you can use this regulation to manage the available bandwidth between masters.


  • QOSOVERRIDE[x] has no effect on outstanding transaction rate regulation.

  • Only transactions that have data associated with them are counted for QoS regulation. These transactions are:

    • ReadNoSnoop

    • ReadOnce

    • ReadShared

    • ReadClean

    • ReadNotSharedDirty

    • ReadUnique

    • WriteNoSnoop

    • WriteUnique

    • WriteLineUnique

    • WriteClean

    • WriteBack.

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