AMBA 5 Overview

The Arm AMBA protocols are an open standard, on-chip interconnect specification for the connection and management of functional blocks in a System-on-Chip (SoC). They facilitates right-first-time development of multi-processor designs with large numbers of controllers and peripherals.

  • AMBA 5 CHI Specification

    AMBA 5 CHI (Coherent Hub Interface) specification adds a new protocol for the interface architecture, highly scalable SoCs required by many server and networking applications.

    AMBA 5 CHI Protocol Specification
  • AMBA 5 AHB5 Specification

    AHB5 complements the Armv8-M architecture to extend the TrustZone security foundation from the processor to the system.

    AMBA 5 AHB5

AMBA 5 CHI Description

The AMBA 5 CHI (Coherent Hub Interface) architecture specification defines the interfaces for connection of fully coherent processors, such as the Cortex-A75 and Cortex-A55, and dynamic memory controllers, such as the CoreLink DMC-620, to high performance, non-blocking interconnects such as the CoreLink CMN-600. It is appropriate for a wide range of applications that require coherency including mobile, networking, automotive and data center.

The CHI specification separates the protocol and transport layers to allow differing implementations to provide the optimal trade-off between performance, power and area. This separation allows interconnect designs ranging from an efficient, small cross-bar to high performance, large scale mesh network.

CHI has been architected to maintain performance as the number of components and quantity of traffic rises.  This includes placing additional requirements on masters to respond to coherent snoop transactions, which means forward progress for particular masters can be more easily guaranteed in a congested system. The separation of the identification mechanism into master identifiers and transaction identifiers allows the interconnect to be constructed in a more efficient manner.

The protocol also provides a Quality of Service (QoS) mechanism to control how resources in the system shared by many processors are allocated without needing a detailed understanding of every component and how they might interact.

The AMBA 5 CHI specification is currently available to partners integrating SoCs or developing IP or tools that implement it.  Please contact your Arm account manager for details on obtaining a copy. 

AMBA 5 CHI Performance

The latest generation, highest performance AMBA 5 interface called CHI (Coherent Hub Interface) is targeted to provide performance with efficiency at any design point, from mobile phone to high performance computing applications. Some of the key features include:

  • Support for high frequency, non-blocking coherent data transfer between many processors.
  • A layered model to allow separation of communication and transport protocols for flexible topologies such as a cross-bar, ring, mesh or ad hoc.
  • Cache stashing to allow accelerators or IO devices to stash critical data within a CPU cache for low latency access.
  • Far atomic operations enable the interconnect to perform high frequency updates to shared data.
  • End-to-end data protection and poisoning signaling.

AMBA 5 AHB5 Overview

The AMBA 5 AHB5 (Advanced High-performance Bus) architecture specification is an interface protocol most widely used with Cortex-M processors for embedded designs and other low latency SoCs.

AHB5 builds upon the previous generation AHB-Lite specification with two key goals:

  1. It complements the Armv8-M architecture and extends the TrustZone security foundation from the processor to the entire system.
  2. It provides consistency and alignment with AMBA AXI4 specification to:
    • Ease integration of Cortex-A and Cortex-M based systems in an SoC.
    • Allow a unified TrustZone security solution inclusive of AXI and AHB systems.

The new properties introduced in the specification are:

  • Secure/Non-secure signaling in address phase to indicate secure or non-secure transactions.
  • Extended memory types to support more complex systems.
  • Exclusive transfers that support semaphore-type operations.

AMBA 5 AHB5 provides further clarifications of AHB-Lite protocol properties as they become more widely adopted:

  • Multiple slave select for area efficiency.
  • Single-copy and multi-copy atomicity enabling scaling to multiple cores.
  • User signaling allowing for user extensions and consistency with the AMBA 4 AXI specification.

The AHB5 specification is available now for download by partners intending to build next-generation SoCs for applications including real time, IoT and embedded microcontroller designs.