Data General AViiON Series, Клиентская документация

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Assigning VME Data Bus and Interrupt Priorities
E-6
014–001867
If you believe you are having performance problems due to DTB priorities and
cannot set up the system properly due to physical constraints, evaluate what other
changes you can make to the system environment.
Board Related Problems
Boards sold by Data General are exhaustively tested to ensure that they meet VME
specifications in all Data General system environments, thus they should not cause
a problem.
However, if you have added a non–DGC board and unusual problems begin to occur,
then suspect a board–related problem. A board may meet the VMEbus specification,
yet in some environments may cause a VMEbus violation or be affected by a
violation from another board.
Most of the time the only symptom of a problem is the corruption of data on the bus.
Such problems are particularly troublesome because the VMEbus specification
provides no way of isolating the problem. Unless detected by diagnostic programs
such as RBOS, a failure of this type usually causes a catastrophic system failure,
such as a system panic.
If you are having a problem with the VMEbus, things to look for are
D Has the system been modified in any way (new board added, bad board replaced,
boards moved on the VMEbus, etc.) prior to the failure occurring?
D
Does the failure symptom indicate a memory address problem, such as trying to
access a protected area of memory?
D
Is data corruption occurring? Backup data does not compare with original, or
program executable code does not execute properly.
If you believe that a VME controller board is causing data corruption, contact your
Data General support service office as soon as possible.
If the problem started after a system configuration change, return the system to its
original configuration, if you can, until the failure has been properly evaluated by
DGC support personnel.
Bus Clear (BCLR*) Response
BCLR* is driven by the arbiter to communicate to the current bus master, that a
higher priority request is pending; thus, the current bus master may release the bus
at the conclusion of the current transfer cycle.
General Rules for Setting DTB Priority
NOTE: Before using this section, you must be familiar with the information
presented earlier in this appendix.
Use the following rules as a general guide to assigning DTB priority.
1. If your Data General system has two user slots, set both boards to a TDB priority
of 3; priority will then be defined by the board positions (first slot has priority
over the second).