VME Hardware Architecture

VME Hardware Architecture

The VME bus interface circuitry for Challenge and Onyx systems resides on a mezzanine board called the VMEbus Channel Adapter Module (VCAM) board. One VCAM board is standard in every system and mounts directly on top of the IO4 board in the system card cage.

The IO4 board is the heart of the I/O subsystem. The IO4 board supplies the system with a basic set of I/O controllers and system boot and configuration devices such as serial and parallel ports, and Ethernet.

In addition, the IO4 board provides these interfaces:

two Flat Cable Interconnects (FCIs) for connection to Card Cage 3 (CC3)
two SCSI-2 cable connections
two Ibus connections

A Challenge or Onyx system can contain multiple IO4 boards, which can operate in parallel. (Early versions of the IO4 have a possible hardware problem that is described in Appendix B, "Challenge DMA with Multiple IO4 Boards.")

Main System Bus

The main set of buses in the Challenge and Onyx system architecture is the Everest address and data buses, Ebus for short. The Ebus provides a 256-bit data bus and a 40-bit address bus that can sustain a bandwidth of 1.2 GB per second.

The 256-bit data bus provides the data transfer capability to support a large number of high-performance RISC CPUs. The 40-bit address bus is also wide enough to support 16 GB of contiguous memory in addition to an 8 GB I/O address space.

Ibus

The 64-bit Ibus (also known as the HIO bus) is the main internal bus of the I/O subsystem and interfaces to the high-power Ebus through a group of bus adapters.The Ibus has a bandwidth of 320 MB per second that can sufficiently support a graphics subsystem, a VME64 bus, and as many as eight SCSI channels operating simultaneously.

Bus Interfacing

Communication with the VME and SCSI buses, the installed set or sets of graphics boards, and Ethernet takes place through the 64-bit Ibus. The Ibus interfaces to the main system bus, the 256-bit Ebus, through a set of interface control devices, an I address (IA) and four I data (ID). The ID ASICs latch the data, and the IA ASIC clocks the data from each ID to the Flat Cable Interface (FCI) through the F controller (or F chip).

Two FCI controllers (or F controllers) help handle the data transfers to and from an internal graphics board set (if present) and any VMEbus boards in optional CC3 applications. The SCSI-2 (S1) controller serves as an interface to the various SCSI-2 buses. The Everest peripheral controller (EPC) device manages the data movement to and from the Ethernet, a parallel port, and various types of on-board PROMs and RAM.