Identifying OpenBus System Content

The key objective of Altium Designer's OpenBus System feature is to allow a designer to build a processor-based system in a more streamlined and abstract way. Before taking a closer look at how this is achieved, it's a good idea to identify which part of an FPGA design is targeted by this system.

A processor-based FPGA design can essentially be divided into two parts:

• Main Processor System – containing the processor and peripherals, as well as the interconnect and bus mastering components.

• Interface Circuitry – this includes the wiring between the peripheral devices and the physical pins of the FPGA device (depicted by port components). This also includes any additional interface logic.

Figure 1 illustrates this division for an existing design.

Figure 1. Identifying the components of a processor-based FPGA design.

Altium Designer's OpenBus System feature is concerned purely with the representation of the main processor system within an FPGA design.

In an FPGA design that utilizes this system, the interface circuitry remains on the schematic top-sheet – remember that all FPGA design projects in Altium Designer must have a top-level schematic. The main processor system is defined in a separate, OpenBus System document (*.OpenBus). Connectivity between the two is made through a sheet symbol placed on the schematic.

Figure 2. Example structure of an FPGA design
using the OpenBus System.

So how exactly does one go about building an OpenBus System in AltiumDesigner? The whole process can be broken down into three key stages:

• Place and wire the required devices that comprise the main processor system – this is then the OpenBus System.

• Configure the OpenBus System

• Connect the OpenBus System to the remaining interface circuitry of the FPGA design, resident on the top-level schematic sheet.