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AMBA AHB vs AXI | difference between AMBA AHB and AMBA AXI

This page compares AMBA AHB vs AXI and mentions difference between AMBA AHB and AMBA AXI interface bus types.

Introduction: The full form of AMBA is Advanced Micro-controller bus architecture. It defines AMBA protocols which can be used for connections on the board consisting of various functional blocks and peripherals in addition to more than one microcontrollers and microprocessors. The board where AMBA is best suited consists of one or more µCs, one or more µPs, memort elements, DSPs, DMAs, USBs, PCI, I2C, peripherals and so on.

AMBA standard evolution timeline

AMBA standards are defined for various bus types viz. AHB (Advanced High performance Bus) , ASB (Advanced System Bus), APB (Advanced Peripheral Bus), ATB (Advanced Trace Bus) and AXI (AMBA Extensible Interface). The figure-1 mentions AMBA standard evolution timeline.

AMBA AHB

AMBA AHB is designed for high performance and high clock frequency system modules. AHB supports efficient connection of processors, on-chip memories and off chip external memory interfaces. The AMBA AHB offers 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).

AMBA AHB Architecture

The figure-2 depicts AMBA based SoC design which uses AHB or ASB protocols for high bandwidth interconnect and APB protocol for low bandwidth peripheral interconnects. AHB to APB bridge or ASB to APB bridge is used to connect high bandwidth and low bandwidth peripherals together.

AMBA AXI

AMBA AXI is designed for high performance, high frequency and high speed submicron interconnect. It is suitable for high bandwidth and latency designs. It is backward compatible with previous interfaces such as AHB and APB. It enables high frequency operation without use of complex bridges.

AMBA AXI architecture

There are different versions of AXI interfaces which include AXI3, AXI4 and AXI-Lite as defined in various standard specifications. As shown in the figure-3, AXI system consists of number of master and slave devices which are connected together using some form of interconnects.

Difference between AMBA AHB and AMBA AXI

Following table mentions comparison between AMBA AHB and AMBA AXI.

Features AMBA AHB Bus AMBA AXI Bus
• Architecture Single channel, Shared bus Multi channel, read/write optimized bus
• Bus width and Speed 128 bit bus running at 400 MHz 64 bit bus running at 200 MHz
• Burst mechanism Address and data are locked together (single pipeline stage), HREADY controls intervals for address and data
• Requires transmitting address of every data item transmitted on the bus
One address for entire burst, simultaneous read and write transactions
• better bus utilization as burst mode requires transmitting address of only first data item on the bus.
• Throughput Good Excellent
• Latency Excellent Good
• Power consumption Low High
• Burst mode No fixed burst mode Fixed burst mode for memory mapped I/O peripherals
• Access No exclusive access support Exclusive data access (semaphore operation) support
• Security Simple protection and cache hint support Advanced security and cache hint support
• Timing Isolation No inherent support for timing isolation Register slice support for timing isolation
• Power interface No low power interface Native low power clock control interface
• Topology Default hierarchical bus topology support default bus matrix topology support

Also refer advantages and disadvantages of AMBA AHB bus, AMBA AXI bus, PCI Bus and PCI Express.



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