OpenBoot Features

The OpenBoot architecture provides a significant increase in functionality over the boot PROMs in earlier Sun systems. Although this architecture was first implemented on SPARC systems, its design is processor-independent. Some notable features of the OpenBoot firmware include:

• Plug-in device drivers. A plug-in device driver is usually loaded from a plug-in device such as an SBus card. The plug-in device driver can be used to boot the operating system from that device or to display text on the device before the operating system has activated its own drivers. This feature allows the input and output devices supported by a particular system to evolve without changing the system PROM.

• FCode interpreter. Plug-in drivers are written in a machine-independent interpreted language called FCode. Each OpenBoot system PROM contains an FCode interpreter. Thus, the same device and driver can be used on machines with different CPU instruction sets.

• Device tree. The device tree is an OpenBoot data structure describing the devices (permanently installed and plug-in) attached to a system. Both the user and the operating system can determine the hardware configuration of the system by inspecting the device tree.

• Programmable user interface. The OpenBoot user interface is based on the interactive programming language Forth. Sequences of user commands can be combined to form complete programs. This provides a powerful capability for debugging hardware and software.