AMBA AHB: Advantages and Disadvantages

This page explores the advantages and disadvantages of the AMBA AHB bus. It highlights the benefits and drawbacks associated with this architecture.

Introduction:

AMBA, which stands for Advanced Microcontroller Bus Architecture, is a bus architecture specifically designed for microcontrollers. It’s an open standard that defines on-chip interconnect specifications for connecting and managing functional blocks within a System on Chip (SoC). AMBA allows for the use of a large number of peripherals and their connection to one or more microcontrollers or microprocessors.

AMBA standards cover various bus specifications across different versions, including:

• Advanced High-Performance Bus (AHB)
• Advanced System Bus (ASB)
• Advanced Peripheral Bus (APB)
• Advanced Trace Bus (ATB)
• AMBA Extensible Interface (AXI)

What is AMBA AHB?

AMBA AHB is engineered for high-performance and high-clock-frequency system modules. It facilitates the efficient connection of processors, on-chip memories, and off-chip external memory interfaces.

AMBA AHB provides high performance, pipelined operation, multiple bus masters, burst transfers, split transactions, single clock edge operation, single-cycle bus master handover, non-tristate implementation, and wide data bus configurations (64/128 bits).

Figure 1: AMBA AHB Architecture

Figure 1 illustrates an AMBA-based SoC design that uses AHB or ASB protocols for high-bandwidth interconnects and the APB protocol for low-bandwidth peripheral interconnects. An AHB to APB bridge or ASB to APB bridge is used to connect high-bandwidth and low-bandwidth peripherals together.

A typical AMBA AHB system consists of:

• AHB Master: Initiates read and write operations using address and control information. Only one bus master can use the bus at a time.
• AHB Slave: Responds to read or write operations according to the address space range.
• AHB Arbiter: Ensures that only one bus master initiates data transfers at any given time. The protocol is fixed, but the arbitration algorithm can be implemented based on application requirements.
• AHB Decoder: Decodes the address of each transfer and provides a select signal for the slave. A single centralized decoder is needed in all implementations.

Refer to the AMBA AHB protocol specifications for further details.

Benefits or Advantages of AMBA AHB

The following are the benefits or advantages of AMBA AHB:

• Offers high performance, pipelined operation, and high bandwidth.
• Supports multiple bus masters, burst transfers, and split transactions.
• AHB can be implemented as a single shared bus, hierarchical bus, or bus matrix.
• Bus arbitration solves many ordering problems.
• Easy to add new blocks.
• Excellent latency and low power consumption.
• Delivers cheaper boards.

Drawbacks or Disadvantages of AMBA AHB

The following are the drawbacks or disadvantages of AMBA AHB:

• Has a bandwidth bottleneck.
• Does not scale well when blocks are added.
• Multiple outstanding transactions are not handled well.

Also, refer to the advantages and disadvantages of the AMBA AXI bus and the difference between AMBA AHB and AXI bus types.