Difference Between AHB And AXI (With Table)

All bus masters are bus masters: AHB and AXI. They are both parts of the AMBA (Advanced Microcontroller Bus Architecture). System Design with high performance, bandwidth, & frequency in mind is the goal. The two bus masters are correlated, but they differ in many ways, and the distinctions are detailed in the following article.

AHB vs AXI

The main difference between AHB and AXI is that AHB is designed to be a single-channel bus, on the other hand, AXI is not. This multi-channel bus is tuned for both read and write performance. It is also more helpful for on-chip communication and ASIC verification than the AXI protocol, which can be more cumbersome.

An example of a single channel bus is the Advanced High-performance Bus, a widely popular protocol among ARM customers. Each bus master can only have a single outstanding transaction at a time, and dealings with AHB have bus latencies starting at 16 Bytes. Single-edge clock protocol, split transactions, huge bus widths, and locked transfers are just a few of the features of the AHB.

As previously stated, AXI is a multi-channel bus with five channels: a Read data channel, a Write data channel, a write address channel, a Write response channel, and an Address channel. The Read data channel, Write data channel, and the Address channel are the only channels that can be used to transfer data. Several open transactions can be handled by AXI simultaneously. AXI’s bus latencies begin at 64 Byte transactions, the minimum for a single transaction. In addition to QoS, write strobes, and full-duplex communication mode, AXI has several additional characteristics.

Comparison Table Between AHB and AXI

Parameters of ComparisonAHBAXI
Full formbus technology that is both advanced and high-performanceExtensible Interface with Advanced Functionality
ChannelOne channel is available on this bus.As the name implies, it is a bus with multiple data transmission channels.
FeaturesThe early termination of bursts, as well as locked transfersQoS, Write Data Interleaving, unaligned data transfer, and byte invariance are all features of the XML 1.1 specification.
Address space assigned for a single enslaved personThe file size for AHB is 1 KB.AXI has a file size of 4 kilobytes.
Burst LengthsThe AHB has burst lengths 1, 2, 6, and 16 seconds. The INCR kinds are the exception.AXI3 burst lengths range from 1-16, while AXI4 burst lengths range from 1-256.

What is AHB?

Advanced High-performance Bus (sometimes known as AHB) is an acronym. It is a single-channel bus that is also a shared bus. It has one address channel, one read data channel, and one write data channel, all of which are connected. A simple transaction with AHB requires only two bus cycles, one for the address phase and the other for the data phase. The bus widths at AHB are pretty significant.

Users unable to achieve the timing criteria in AHB will not be able to use the pipeline that registers in their path because the channel will be ignored. Furthermore, because it cannot accommodate the insertion of pipeline registers, it does not allow for a higher frequency but instead restricts the highest frequency that the architecture can achieve.

AHB does not support the Quality of Service (QoS) feature, write strobes or Exclusive support. It only handles transfers that are locked. It has a low power dissipation rating and a low throughput rating. AHB also has predetermined burst lengths, which is a nice feature. In INCR, the burst can last for any amount of time. However, the exact duration is not disclosed.

The ARM limited firm released the AHB protocol in AMBAversion 2, and it quickly became a prevalent protocol until the new version AXI was introduced.

What is AXI?

AXI is an abbreviation for Advanced eXtensible Xtensible Interface. It is a multi-channel bus intended for use in on-chip communication systems. It is a high-performance, high-frequency communication interface that operates in Full-duplex mode. Every channel in AXI is entirely independent of the others, and there is five total. Those channels are as follows: Write address channel (AW), Write data channel (W), Read data channel (R), Read address channel (AR), Write response channel (WR), Write response channel (WR), and Write response channel (B).

Because AXI has five parallel channels flowing simultaneously, many wires are required to build out the layout. A pipeline register can be placed anywhere in the course of any one of the channels by the user, allowing AXI to operate at a higher frequency as a result of this capability.

In addition to unaligned data transfer (using strobes), AXI supports separate address and control phases, byte invariant transactions, burst-based transactions with start addresses issued, Quality of Service, out-of-order transaction completion, Write Data Interleaving (WDI), and atomic operations. AXI contains other signaling systems such as AxRegion and AxUser, described below.

AXI is a burst-based protocol, which implies that it allows for many data transfers for a single request to be processed. When a massive volume of data must be sent from or to addresses that follow a given pattern, it makes the process simpler. This information is known from the beginning, and the lengths of these bursts can range from 1-16 for AXI3 and 1-256 for AXI4.

Main Differences Between AHB and AXI

  1. AHB is an abbreviation for Advanced High-performance Bus, a single channel bus with advanced features.
  2. AHB does not support completing “out of order transactions,” whereas AXI does keep the completion of “out of order transactions.”
  3. The power dissipation of AHB is minimal, whereas the power dissipation of AXI is considerable.
  4. The utilization of the AHB Bus is higher when compared to the utilization of the AXI Bus, which consumes 50% more power.
  5. In contrast to AHB, AXI provides capabilities such as unaligned data transport utilizing strobes and byte invariance, which AHB does not support.
  6. Write strobes are not supported by AHB, although AXI supports them.
  7. AHB supports the locked transfer. In the instance of AXI, the AXI 3 supports the locked transfer. However, the AXI4 does not support this feature.
  8. AHB does not support exclusive transfers. However, they are supported by AXI.
  9. Compared to the AXIs, the bus latencies of the AHB bus master begin at a lower level.

Conclusion

Amiga (Advanced Microcontroller Bus Architecture) is a bus that includes both the AXI and AHB modules. Each of the bus masters must be connected to a single-channel shared bus for the Advanced High-Performance Bus, also known as AHB, to function correctly. It is impossible to use the full-duplex mode with the AHB bus master.

Its abbreviation is AXI, which stands for Advanced extensible Interface and refers to a multi-channel bus. A total of five separate channels are available on this device. Due to many channels, AHB is a full-duplex form of communication support bus master. AXI provides capabilities such as unaligned data transfer (using strobe), QAS, Semaphore mode of operation, byte invariance, and Write Data Interleaving, to name a few examples. AmbA is the third version of the AMBA technology.

References

  1. https://ieeexplore.ieee.org/abstract/document/5783594/
  2. https://iopscience.iop.org/article/10.1088/1742-6596/1993/1/012008/meta