AHB vs APB: Difference and Comparison

When making comparisons, the AHB employs full-duplex parallel communications, whilst the APB employs huge memory-I/O operations. The AHB and the APB use chip Bus specifications. The Advanced High-performance Bus makes waits, faults, and bursts possible. The pipelined ADH primarily links to storage.

Key Takeaways

1. AHB (Advanced High-performance Bus) is a high-performance bus protocol connecting high-speed peripherals. At the same time, APB (Advanced Peripheral Bus) is a low-power bus protocol for connecting slower peripherals.
2. AHB is used for high-speed communication between different components on a chip, while APB is used for low-speed communication between the processor and other peripherals.
3. AHB is a synchronous protocol, while APB is an asynchronous protocol.

AHB vs APB

AHB (Advanced High-performance Bus) is a type of ARM Technology bus system used for high-performance, high-clock-frequency system modules. APB (Advanced Peripheral Bus)  is a type of bus system in ARM Technology that is used for low-bandwidth, low-power peripherals, providing a less complex, lower-cost interface.

AHB seems to be a bus protocol that was first proposed in ARM Ltd’s Advanced Microcontroller Bus Design version 2 publication. Mostly on AHB, a basic transaction consists of just an addressing phase followed by a data phase. A MUX is used to restrict access to a particular device, allowing only one bus master to use it at the moment.

The APB (Advanced Peripheral Bus) is a simple, relatively low, reduced peripheral bus designed for slow electronics. The SoC processors, storage drivers, on-chip storage, and DMA sensors all dangle off the network interface in a typical setup. It is in charge of the processor’s elevated bus links.

Comparison Table

Parameters of Comparison	AHB	APB
Stands for	Advanced High-Performance Bus is the abbreviation for AHB.	Advanced Peripheral Bus is the abbreviation of APB.
Way of Communicating	AHB communicates in full-duplex parallel mode always.	APB makes extensive use of memory I/O for communication.
Based on Usage	It is slightly more complex and tough to use when compared to its peer.	When it comes to operation, the APB is more straightforward than the AHB.
Pipelining	There is a lot of pipelining in the AHB, which might lead to consequences.	There’s also no pipelining in APB compared to AHB.
Used for	It is used for both low as well as high bandwidth control accesses.	The Advanced Peripheral Bus will only be utilized for limited latency control accesses as contrasted to the Advanced High-performance Bus.

What is AHB?

In AMBA 2.0, the AHB got added as a new feature. It was modified to make elevated designs possible. Split operations, single-cycle bus master changeover, single-clock-edge functioning, and broader data bus setups (64/128 bits) were among the additional features implemented.

From the outside, the lords and vassals and AHB must have several parts. A location and control expander, a scan multiplexer, a writing multiplexer, a decode, as well as an arbitrator are among the elements. The addressing signals (HADDR), the writing data bus (HWDATA), as well as the reading data bus (HWDATA), are all shown (HRDATA). The location is used to pick a slave, the writing data bus is used to transmit information from owner to slave, and also the reading data bus is often used to transfer data from servant to master.

A master should first make a message to the arbiter before seizing ownership of the bus. The arbiter provides access depending on a priority system that guarantees masters with top importance get access first. AMBA has not specified this priority mechanism. Hence it will vary from design to design. 

The route, breadth, and kind of data flow are all defined by a multitude of signal amplification. The master’s IP message is decoded into slave-choose impulses by the AHB decoder. The master receives an HRESP signal from the slave, and also the data transmission between the owner and serf commences.

What is APB?

The APB does not support breaking as just a simple bus. There are two phases in each contract: an addressing cycle (Setup phase) as well as a data cycle (Enable phase). A single clock, PCLK, is used on the bus. The bus brings PSEL and PWRITE during Configure, and the destination is placed upon the PADDR address bus. It puts PENABLE up and puts data on the PWDATA/PRDATA bus inside the Enable condition. On the following clock, the enable indication, PENABLE, gets de-asserted.

The Advanced Microcontroller Bus Architecture (AMBA) protocol team comprises the APB. Time limiters interrupt drivers, UARTs, I/O ports, and other sign-up accessories are commonly utilized. Minimum power usage and interface complexities have been optimized. The APB interface does not use pipelines. Each transmission in APB requires at least two rounds (Setup cycle and Access cycle).

Lower-powered peripherals are the focus of the AMBA APB. AMBA APB has been tuned for low energy consumption and decreased interface complexities to enable peripheral operations. The APB protocol could be used with any iteration of the system bus.

Main Differences Between AHB and APB

1. Advanced High-Performance Bus is the abbreviation for AHB. On the other hand, Advanced Peripheral Bus is the abbreviation of APB.
2. AHB communicates in full-duplex parallel mode always, whereas APB makes extensive use of memory I/O for communication.
3. AHB is slightly more complex and tough to use when compared to its peer. On the other hand, when it comes to operation, the APB is more straightforward than the AHB.
4. There is a lot of pipelining in the AHB, which might lead to consequences, whereas there’s also no pipelining in APB compared to AHB.
5. AHB is used for both low as well as high-bandwidth control accesses. When compared, The Advanced Peripheral Bus will only be utilized for limited latency control accesses as contrasted to the Advanced High-performance Bus.

References

1. https://d1wqtxts1xzle7.cloudfront.net/51490114/O0701018790.pdf?1485238518=&response-content-disposition=inline%3B+filename%3DDesign_And_Verification_of_AMBA_APB_Prot.pdf&Expires=1623271280&Signature=Jz2ICAKVzQmveWgfRO7i5x7hVnLxHfPfJx9sFjW9YYmv5JEYx6c1sCo-Pdaw3nLr5qVfbdLpvxE1M9cppaTzyJqR0S5O13qwG4XzdqUWrZsJ5WJKuPN7pz2JlI3ym4hwD4UryjpoCi0tPj~iZQMKooMoFY20hbyibUPFfNB9-f4NUbLXAKPgxEySwwZYpJz7LKH9tykDntnFU18uvaEgoFkF5vJasCP~mn6Df5j-d7EIHn5OaqEpx1HvfxVV-yKc~LDHAoaE8IEUJUgLXp9Fd4Z~eVYVT5SOhB3TCZtCaeTv~yrhs1zdR-McSMPxQTmpyqiEfZc0ylMK96NgmdWDvg__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA
2. https://www.sciencedirect.com/science/article/abs/pii/S1388245713009711