Traffic Types

Versal ACAP Technical Reference Manual (AM011)

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1.4 English

Three different traffic types are defined:

  • Low latency: typically CPU to DDR memory transactions
  • Isochronous: real-time deadlines
  • Best effort: bulk transfers and not time critical

Low Latency Transactions

For high-priority transactions, low latency is the key for meeting performance requirements. The APU and RPU MPCores can specify low latency transactions so their memory access requests are serviced in a timely manner to avoid or minimize CPU pipeline stalls.

Low latency transactions are usually associated with cache fill and replacement.

Video Isochronous Transactions

Another category of masters that can live with longer latency in typical conditions is isochronous (or video class) transactions. However, there is critical moment (maximum latency) in which data must be available without causing a system degradation. The key requirement is a guaranteed maximum latency. The example masters are video encoder, camera sensor, or display device.

Best Effort Transactions

High-throughput and best effort transactions are allowed with long latency but need high throughput to achieve architectural performance goals. These types of masters include DMAs, the CPM, and PL functional units.