AHB vs APB: Difference and Comparison

AHB (Advanced High-performance Bus) and APB (Advanced Peripheral Bus) are two distinct buses commonly used in ARM-based systems. AHB is a high-performance bus designed for connecting faster components like processors and memory, offering high bandwidth and low-latency communication. On the other hand, APB is a slower bus intended for connecting peripheral devices, providing a simpler and more power-efficient interface for slower-speed components.

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

Feature	AHB (Advanced High-performance Bus)	APB (Advanced Peripheral Bus)
Purpose	Connects high-speed peripherals and memory	Connects low-speed peripherals
Performance	High bandwidth, low latency	Low bandwidth, high latency
Data transfer size	Up to 16 beats (32 or 64 bits)	Up to 256 bytes
Complexity	More complex signal interface	Simpler signal interface
Master support	Supports multiple masters	Single master (the processor)
Arbitration	Requires arbitration logic for multiple masters	No arbitration needed
Power consumption	Higher power consumption	Lower power consumption
Cost	More expensive to implement	Less expensive to implement
Typical peripherals	CPUs, DMA controllers, high-speed memory	Timers, GPIOs, I2C, SPI

What is AHB?

The Advanced High-performance Bus (AHB) is a widely used system bus architecture in ARM-based systems. It serves as a key component in facilitating high-speed communication between various hardware components, providing a robust and efficient data transfer infrastructure.

Features and Characteristics

1. High Performance: AHB is designed for high-performance data transfers, making it suitable for connecting critical system components such as processors and memory. Its architecture supports fast and efficient communication, meeting the demands of modern embedded systems.
2. Burst Transfer Capability: AHB incorporates burst transfer capabilities, allowing multiple data transfers in a single bus cycle. This feature enhances the overall efficiency of data exchanges between the master and slave devices connected to the bus.
3. Multi-layered Bus Architecture: AHB features a multi-layered architecture, which includes the AHB master, AHB slave, and the system bus matrix. This hierarchical structure facilitates efficient connectivity, enabling various peripherals and components to communicate seamlessly.
4. Support for Split Transactions: AHB supports split transactions, allowing the master device to release the bus temporarily while it performs other tasks. This feature enhances overall bus utilization and responsiveness in dynamic system scenarios.
5. Scalability: The AHB bus architecture is scalable, accommodating a range of system complexities. It provides the flexibility to scale up or down based on the specific requirements of the embedded system, making it adaptable to diverse application scenarios.

Applications

AHB is commonly utilized in a variety of applications, including microcontrollers, digital signal processors, and other embedded systems requiring high-speed and efficient data transfer between critical components.

What is APB?

The Advanced Peripheral Bus (APB) is a widely used bus architecture in ARM-based systems, specifically designed for connecting peripheral devices to the system. It provides a low-power and efficient communication interface for slower-speed peripherals.

Key Features

1. Simplicity and Efficiency:
   • APB is characterized by its simplicity, making it well-suited for connecting slower peripheral devices.
   • It utilizes a straightforward, single-master, multiple-slave architecture, streamlining communication with peripherals.
2. Low-Speed Devices:
   • APB is ideal for interfacing with low-speed peripherals such as timers, UARTs, and I/O controllers.
   • The bus architecture optimizes power consumption, making it suitable for devices that do not require high-speed communication.
3. Clock Domain Independence:
   • APB operates independently of the system clock, allowing peripherals to have their own clock domains.
   • This feature enables flexibility in connecting peripherals with varying clock requirements without impacting the overall system performance.
4. Synchronous Operation:
   • APB operates synchronously, simplifying the design and ensuring predictable timing characteristics.
   • The synchronous nature of APB aids in easy integration and synchronization of data between the microcontroller and connected peripherals.

Use Cases

APB finds extensive usage in microcontroller and embedded systems where a variety of peripheral devices need to be interfaced with the main processing unit. Its design focuses on resource efficiency and simplicity, making it well-suited for applications where low-power consumption and moderate data transfer rates are crucial.

Main Differences Between AHB and APB

• Purpose:
  • AHB (Advanced High-performance Bus): Designed for high-performance communication between critical components such as processors and memory.
  • APB (Advanced Peripheral Bus): Tailored for connecting peripheral devices, providing a simpler and more power-efficient interface for slower-speed components.
• Speed and Bandwidth:
  • AHB: Offers high bandwidth and low-latency communication, suitable for high-speed data transfer between fast components.
  • APB: Geared towards slower-speed peripherals, emphasizing simplicity and efficiency over high-speed data transfer.
• Device Types:
  • AHB: Primarily used for connecting processors, memory, and other high-performance components within the system.
  • APB: Specifically designed for interfacing with low-speed peripheral devices such as timers, UARTs, and I/O controllers.
• Complexity:
  • AHB: Features a more complex architecture with support for multiple masters and slaves, suited for high-performance systems.
  • APB: Characterized by simplicity, using a single-master, multiple-slave architecture, making it suitable for less complex peripheral connections.
• Clock Domain:
  • AHB: Typically operates synchronously with the system clock, ensuring coordinated data transfer between components.
  • APB: Operates independently of the system clock, allowing peripherals to have their own clock domains, providing flexibility in clock management.
• Use Cases:
  • AHB: Commonly employed in scenarios where high-speed communication between critical components is essential, such as in advanced microprocessors.
  • APB: Widely used in microcontroller and embedded systems where a variety of peripheral devices with lower data transfer requirements need to be connected.
• Power Consumption:
  • AHB: Emphasizes high-performance data transfer, potentially leading to higher power consumption.
  • APB: Optimized for lower power consumption, making it suitable for devices with less demanding communication requirements.

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