Avalon® Interface Specifications

ID 683091
Date 9/26/2022
Document Table of Contents

5.1. Terms and Concepts

The Avalon® -ST interface protocol defines the following terms and concepts:
  • Avalon® Streaming System—An Avalon® Streaming system contains one or more Avalon® -ST connections that transfer data from a source interface to a sink interface. The system shown above consists of Avalon® -ST interfaces to transfer data from the system input to output. Avalon® -MM control and status register interfaces provide for software control.
  • Avalon® Streaming Components—A typical system using Avalon® -ST interfaces combines multiple functional modules, called components. The system designer configures the components and connects them together to implement a system.
  • Source and Sink Interfaces and Connections—When two components connect, the data flows from the source interface to the sink interface. The Avalon® Interface Specifications calls the combination of a source interface connecting to a sink interface a connection.
  • Backpressure—Backpressure allows a sink to signal a source to stop sending data. Support for backpressure is optional. The sink uses backpressure to stop the flow of data for the following reasons:
    • When the sink FIFOs are full
    • When there is congestion on its output interface
  • Transfers and Ready Cycles—A transfer results in data and control propagation from a source interface to a sink interface. For data interfaces, a ready cycle is a cycle during which the sink can accept a transfer.
  • Symbol—A symbol is the smallest unit of data. For most packet interfaces, a symbol is a byte. One or more symbols make up the single unit of data transferred in a cycle.
  • Channel—A channel is a physical or logical path or link through which information passes between two ports.
  • Beat—A beat is a single cycle transfer between a source and sink interface made up of one or more symbols.
  • Packet—A packet is an aggregation of data and control signals that a source transmits simultaneously. A packet may contain a header to help routers and other network devices direct the packet to the correct destination. The application defines the packet format, not this specification. Avalon® -ST packets can be variable in length and can be interleaved across a connection. With an Avalon® -ST interfaces, the use of packets is optional.