VME Bus Addresses and System Addresses

VME Bus Addresses and System Addresses

Devices on the VME bus exist in one of the following address spaces:

The 16-bit space (A16) contains numbers from 0x0000 to 0xffff.
The 24-bit space (A24) contains numbers from 0x00 0000 to 0xff ffff.
The 32-bit space (A32) uses numbers from 0x0000 0000 to 0xffff ffff.
The 64-bit space (A64), defined in the revision D specification, uses 64-bit addresses.

The Silicon Graphics system bus also uses 32-bit or 64-bit numbers to address memory and other I/O devices on the system bus. In order to avoid conflicts between the meanings of address numbers, certain portions of the physical address space are reserved for VME use. The VME address spaces are mapped, that is, translated, into these ranges of physical addresses.

The translation is performed by the VME bus controller: It recognizes certain physical addresses on the system bus and translates them into VME bus addresses; and it recognizes certain VME bus addresses and translates them into physical addresses on the system bus.

Even with mapping, the entire A32 or A64 address space cannot be mapped into the physical address space. As a result, no Silicon Graphics system provides access to all of the VME address spaces. Only parts of the VME address spaces are available at any time. The mapping methods of the Silicon Graphics Crimson series differ from the methods of the later Challenge and Onyx series of machines.

User-Level and Kernel-Level Addressing
PIO Addressing and DMA Addressing
PIO Addressing in Challenge and Onyx Systems
PIO Addressing in the Crimson Series
DMA Addressing