Hard Processor System Technical Reference Manual: Agilex™ 5 SoCs

ID 814346
Date 7/19/2024
Public
Document Table of Contents

4.1.5.8. Credits and Resources

To alleviate congestion and manage resources in CDTI, credit counters are implemented for certain protocol message types. Credits are explicitly assigned to CMD, SNP, MRD, and RB messages. Remaining messages such as, STR, DTR, and DTW are implicitly controlled by credits defined for other messages. For example, DTW messages are limited by RB messages.

The credit values must be configured based on round trip latencies. Initiating CCU component implements credit counters to track messages it initiates. Similarly, target CCU component implements recourses to accommodate all messages it can receive. Each component is further explained.

For each CAIU/NCAIU, the following credit counters are implemented:

  • CMD message credit counter per instance of DCE
  • CMD message credit counter per instance of DMI
  • CMD message credit counter per instance of DII
  • CMD message credit counter for DVE which limits the number of DVM commands. This is implemented in all CAIUs only.

For each DCE, the following credit counters are implemented:

  • SNP message credit counter per instance of CAIU/NCAIU
  • MRD message credit counter per instance of DMI
  • RB message credit counter per instance of DMI

For each DMI/DII, the following counter is implemented:

  • RB message counter

For DVE, the following credit counter is implemented:

  • SNP message counter per DVM capable instance of CAIU/NACIU

The following diagram shows an overview of the credit counters.

Figure 26. Credit Counters Overview

For each CAIU/NCAIU, the following resources are implemented based on message credits:

  • Snoop transaction table, this transaction table is sized based on SNP message credits

For each DCE, the following resources are implemented based on message credits:

  • CMD message skid buffer which is sized based on CMD message credits

For each DMI, following resources are implemented based on message credits:

  • CMD message skid buffer which is sized based on CMD message credits
  • MRD message skid buffer which is sized based on MRD message credits
  • RB control entries which are sized based on RB message credits for both DCE and DMI

For each DII, the following resources are implemented based on message credits:

  • CMD message skid buffer which is sized based on CMD message credits
  • RB control entries which is sized based on RB message credits

In addition to above resources, CCU components are configured with additional resources to achieve required throughput. These resources are configured based on round-trip latencies.

For each CAIU/NCAIU, following resources are implemented:

  • Outstanding transaction table control entries which limit the number of outstanding transactions the CAIU/NCAIU can have at a given time.

For each DCE, the following resources are implemented

  • Active transaction table control entries which limit the number of active transactions each DCE can have at a given time.

For each DMI/DII, the following resources are implemented:

  • Read transaction table control entries which limit the number of read transactions each DMI/DII can have outstanding on the AXI interface
  • Write transaction table control entries which limit the number of write transactions each DMI/DII can have outstanding on the AXI interface

The following diagram shows a resource overview.

Figure 27. Resource Overview