4.7.1 QoS decoding

QoS decoding takes place inside the HN-F.

The QoS decoding is as follows:

  • The CHI interface supports a 4-bit QoS value.
  • The 4-bit QoS has 16 possible values. The following table shows the default map of the QoS classes that the HN-F creates.

    Table 4-1 QoS classes

    QoS value range QoS class Class mnemonic Priority
    15 HighHigh HH Highest
    14-12 High H High
    11-8 Med M Medium
    7-0 Low L Low
  • QoS mapping is fixed and is shown in the qos_band register.

The POCQ is logically partitioned to service different QoS class traffic. The HN-F also uses the priorities in the previous table, where necessary, to arbitrate for the following:

  • Memory controller request selection in the POCQ control block.
  • Data return selection logic, that is, a COMPDATA to a requester.
  • Protocol credits that are sent to an RN-F or RN-I following a protocol-layer retry.

The POCQ resource and buffers are logically partitioned based on the QoS value.

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