AHB

AHB stands for Advanced High-performance Bus, a synchronous on-chip bus protocol in ARM’s AMBA (Advanced Microcontroller Bus Architecture) family. It is designed to provide high-bandwidth, low-latency communication between bus masters and slaves in system-on-chip designs, supporting both single and multi-master configurations through an arbiter. AHB is intended for high-performance peripherals and memory interfaces, offering a higher data throughput than simpler bus standards.

Key features and signaling

AHB uses a pipelined, synchronous transfer protocol driven by a single clock domain. Transfers are controlled by a set of signals that include HADDR (address), HWDATA (write data), HRDATA (read data), HSIZE (transfer size), HBURST (burst type), HTRANS (transfer type), HWRITE (read/write), HSEL (slave select), HMASTLOCK (atomic lock), HREADY (transfer ready), and HRESP (transfer response). It supports burst transfers (SINGLE, INCR, INCRx bursts), allows wait states via HREADY, and provides a mechanism for multiple masters to share the bus with arbitration. Data widths commonly range up to 32 bits, though wider implementations exist.

Architecture and variants

AHB is a high-performance bus intended to replace older, simpler bus architectures within AMBA. It is designed to be compatible with both multi-master and single-master configurations and can accommodate multiple slaves. AHB-Lite is a widely used simplified variant that reduces some features while preserving the essential transfer protocol for single-master, multi-slave systems. The protocol emphasizes efficient use of bandwidth with pipelining and support for bursts, making it suitable for memory interfaces and high-speed peripherals.

Relation to other AMBA buses

AHB sits above lower-bandwidth buses such as APB (Peripheral Bus) in the AMBA hierarchy. While AHB targets high-performance paths, APB provides a simpler, lower-power interface for peripheral devices. Over time, ARM’s AXI (Advanced eXtensible Bus) has become the dominant high-performance bus in newer designs, but AHB remains in use in many existing systems and certain legacy designs.