Advantages of AMBA AXI | Disadvantages of AMBA AXI
This page covers advantages and disadvantages of AMBA AXI bus. It mentions benefits or advantages of AMBA AXI and drawbacks or disadvantages of AMBA AXI.
Introduction: AMBA is the short form of Advanced Micro-controller bus architecture. This open standard defines inter-connection specifications of various modules on a SoC. AMBA helps to design the SoC perfect in its first attempt. It is useful for board development consisting of more than one micro-controllers or micro-processors (i.e. DSPs).
AMBA standards cover various bus specifications in different versions.
• Advanced High Performance Bus (AHB)
• Advanced System Bus (ASB)
• Advanced Peripheral Bus (APB)
• Advanced Trace Bus (ATB)
• AMBA Extensible Interface (AXI)
What is 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.
Following are the key features of AMBA AXI protocol.
• Separate address, control and data phases
• Supports unaligned data transters
• Only start address based burst transactions
• Separate read and write data channels to enable low cost DMA
• Ability to issue multiple outstanding addresses
• Out of order transaction completion
• Easy addition of register stages to provide timing closure.
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-1, AXI system consists of number of master and slave devices which are connected together using some form of interconnects. Following figure-2 mentions timeline of AMBA standard evolution.
AXI protocol defines interfaces between following.
• Between a master and interconnect
• Between a slave and interconnect
• Between a master and a slave
Most of the systems use one of following three interconnect methods.
• Shared address and data buses
• Shared address buses and multiple data buses
• Multi-layer with multiple address and data buses
AXI specifications mention channel architecture for read address, read data, write address, write data and write response channels. Refer AMBA AXI protocol specifications for more information.
Benefits or advantages of AMBA AXI
Following are the benefits or advantages of AMBA AXI:
➨It offers higher throughput compare to AMBA AHB.
➨It offers higher performance than AMBA AHB and APB protocols.
➨It is easier to integrate IP from different domains as well as to develop proprietary IPs.
➨It is widely adopted interface standard. Hence it has support for many partners.
➨AXI protocol supports three different configurations viz. "memory map/full" for OPBv46 replacement, "streaming" for data streaming and "Lite" for simple systems.
Drawbacks or disadvantages of AMBA AXI
Following are the drawbacks or disadvantages of AMBA AXI:
➨It offers higher latency than AMBA AHB.
➨It consumes higher power compare to AMBA AHB.
➨AXI is not a shared bus standard.
➨AMBA AXI4 has limitations with respect to burst data and beats of information to be transferred.
➨Burst must not cross 4K boundary. Burst longer than 16 beats are only supported for INCR burst type.
➨Both WRAP and FIXED burst types remain constrained to maximum burst length of 16 beats.