Accessory based resource offset mechanism for a pci bus in a printer

Abstract

A peripheral device (such as a printer) locates shareable resources on an accessory by using an offset mechanism on the accessory. The offset mechanism includes one or more offset values stored in a first memory location on the accessory. The one or more offset values are indicative of offsets of one or more resources within the accessory memory. The one or more accessory resources are shareable with the peripheral device. A further offset value is stored in a second memory location on the accessory. The further offset value is indicative of an offset for determining the first memory location on the accessory. Additionally, a base address is stored in yet another memory location on the accessory and provides a general reference point for locating the first memory and accessory resources as mapped into the peripheral's memory. In a preferred embodiment, the offset mechanism of the present invention is implemented as an enhanced feature of the PCI Local Bus Specification. For example, the first memory location is disposed in the PCI defined Memory Address Space of the accessory, and the second memory location and base address are both disposed in the PCI defined Configuration Address Space of the accessory. Advantageously, the present invention enables a peripheral device to locate resources on an accessory without knowing in advance where the resources are located on the accessory.