VME-bus Interface Overview

VME-bus Interface Overview

All high-end Silicon Graphics systems--Crimson, CHALLENGE/Onyx, POWER CHALLENGE/POWER Onyx, and the POWER series-- support the VME bus with a VME-bus adapter. Old mid-range systems--IRIS 4D/20, 4D/25, 4D/30, and 4D/35--also supported VME. Silicon Graphics desktop systems--Indigo, Indigo2, and Indy--do not currently support the VME bus.

The VME bus is an industry-standard bus for interfacing devices. It supports the following features:

Seven levels of prioritized processor interrupts
16-bit, 24-bit, and 32-bit data addresses and 64-bit memory addresses
16-bit and 32-bit accesses (and 64-bit accesses in MIPS III mode)
8-bit, 16-bit, 32-bit, and 64-bit data transfer
DMA to/from main memory

The VME bus does not distinguish between I/O and memory space, and it supports multiple address spaces. This feature allows you to put 16-bit devices in the 16-bit space, 24-bit devices in the 24-bit space, 32-bit devices in the 32-bit space, and 64-bit devices in 64-bit space.[8] So you must know which of the four address spaces the board uses when you design a VME device driver.

Note: On some devices, you can use jumpers or switch settings to configure the device to use a particular address space. Some systems have DMA-mapping registers to make memory appear contiguous to the VME card. For additional information on VME-bus operation, see the ANSI standards specification for the VME bus.

[8] 64-bit data transfers, accesses, and memory addresses do not depend on a 64-bit kernel, so they can be mapped to all MIPS R4000 series platforms.

VME-bus Adapter
VME-bus Address Space
VME-bus Read-Modify-Write Cycle
VME-bus Adapter Requests
VME-bus Interrupts
Distribution of VME Interrupts on Multiprocessors