Understanding AXI Protocol – A Quick Introduction

Advanced eXtensible Interface, or AXI, is part of ARM’s AMBA specifications. The AXI is a point to point interconnect that designed for high performance, high speed microcontroller systems. The AXI protocol is based on a point to point interconnect to avoid bus sharing and therefore allow higher bandwidth and lower latency. AXI is arguably the most popular of all AMBA interface interconnect.

The essence of the AXI protocol is that it provides a framework for how different blocks inside each chip communicate with each other. It offers a procedure before anything is transmitted, so that the communication is clear and uninterrupted. That way, different components can talk to each other without stepping on each other. The procedure for the AXI protocol is as follows:

• Master & slave must “handshake” to confirm valid signals
• Transmission of control signal must be in separate phases
• Separate channels for transmission of signals
• Continuous transfer may be accomplished through burst-type communication

The following diagram shows a typical AXI bus interconnect. The processor is connected to the AXI interconnect matrix via the AXI bus. The matrix can support multiple masters and multiple slaves.

By working with the master and slave devices, the AXI protocol works across five addresses that include read and write address, read and write data, and write response. Since each channel has its own unique signal, it can send the handshake response uninterrupted so that it can be received and put into order. That way, the channel that has priority will be responded to first and so forth. The source must provide a valid signal and one that gets a proper response from the receiver.

By having the transmission performed in separate phases, it allows the transfer of information to be performed in an orderly manner. This means that a handshake or agreement is reached first, then the information is moved from the source to the recipient. And that’s how the AXI protocol works to move information between different sources without interference.

With so many devices using the AXI protocol, it makes it easier to connect different devices into the same hub because priority is established. By learning about how the interface works, you can set the priorities for clear communication to occur.