Introduction to AMBA Bus

What is AMBA On-Chip Bus?

With the development of deep sub-micron technology, the scale of Integrated Circuit chips is growing. NumberIC from Time Series-driven design method, to IP Reuse-based Design MethodAnd has been widely used in SoC design.In the SOC design based on IP address multiplexing, on-chip bus design is the most critical issue.. Therefore, many on-chip bus standards have emerged in the industry. Among them, the AMBA On-Chip Bus launched by arm has been favored by the majority of IP developers and SoC system integrators, and has become a popular industrial standard on-Chip structure.AMBA specifications mainly include the AHB (Advanced High Performance Bus) system bus and the APB (Advanced Peripheral Bus) peripheral bus.

AMBAOn-Chip Bus

AMBA 2.0 consists of four parts: AHB, ASB, APB, and test methodology.AHB uses the traditional shared bus with the main module and slave module, and the interfaces and interconnection functions are separated, which is of great significance to the interconnection between modules on the chip. AMBA is not only a bus, but also an interconnection system with interface modules. Next we will briefly introduce the more important AHB and APB bus.

  

AHBIntroduction

AHB is mainly used for the connection between high-performance modules (such as CPU, DMA, and DSP). As an on-chip system bus of SOC, it includes the following features:

★Single clock edge operation,

★Non-triplicate,

★Support for burst transmission,

★Supports multipart transmission,

★Supports multiple master controllers,

★Configurable 32-bit ~ 128-bit bus width,

★Transmission of bytes, half bytes, and words is supported.

The AHB system consists of the main module, slave module, and infrastructure.. The transmission on the whole AHB Bus is sent by the main module, and the slave module is responsible for responding. The basic structure is from the arbiter, the main module to the multi-channel from the module to the main module, the multi-channel from the module to the main module, the decoder (decoder), the virtual slave module (dummy slave) and the virtual master (dummy master. The interconnection structure 1 is shown in.

APB Introduction

APB is mainly used for the connection between peripheral peripherals with low bandwidth.For example, UART, 1284, etc. Its bus architecture does not support multiple main modules like AHB,The only main module in APB is APB bridge.. Its features include two clock-cycle transmission, no waiting period and response signal, simple control logic, and only four control signals. The transmission on APB can be illustrated by the state chart 2.

 

1) The system is initialized to the idle status. At this time, no transmission operation is performed and no slave module is selected.

2) When there is a need for transmission, pselx = 1, penable = 0, the system enters the setup state, and will only stay in the setup State for one cycle. When the next rising edge of pclk arrives, the system enters the enable state.

3) when the system enters the enable state, the paddr, psel, and pwrite in the setup State remain unchanged, and the penable is set to 1. Transmission will only maintain a period in the enable state, and will be completed after setup and enable state. If no data transmission is required, it enters the idle state and waits; if there is continuous data transmission, it enters the setup state.

On-Chip System Based on AMBA 

A typical AMBA-based system diagram 3 is shown.

most modules mounted on the bus (including processors) is only a single attribute function module : The main module or slave module. The main module is a module that sends read/write operations to the slave module, such as CPU and DSP. The slave module is a module that accepts commands and responds to the requests, such as on-chip RAM, AHB/APB bridge. In addition, some modules have two attributes at the same time. For example, Direct Memory Access (DMA) is a slave module during programming, but it must be a master module when the system reads and transmits data. If there are multiple main modules on the bus, the arbitration server is required to determine how to control the access of various main modules to the bus. Although the arbitration specification is part of the AMBA bus specification, the algorithm used is determined by the RTL design engineer, two of the most common algorithms are fixed-priority and cyclic algorithms. A maximum of 16 master modules and any number of slave modules can be deployed on the AHB Bus. If the number of master modules is greater than 16, you need to add a layer of structure (For details, refer to the multi-layer AHB specification launched by arm ). APB is the only main module on APB bus, it is also a slave module on the AHB system bus. its main function is to lock the address, data, and control signals from the AHB system bus, and provide secondary decoding to generate the selection signal of APB peripheral devices, so as to realize the conversion from the AHB protocol to the APB protocol.

  

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Http://www.mcublog.com/blog/user1/5/archives/2006/13553.html