Assigning VME Data Bus and Interrupt PrioritiesE-6 014–001867If you believe you are having performance problems due to DTB priorities andcannot set up the system properly due to physical constraints, evaluate what otherchanges you can make to the system environment.Board Related ProblemsBoards sold by Data General are exhaustively tested to ensure that they meet VMEspecifications in all Data General system environments, thus they should not causea 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 aviolation 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 specificationprovides no way of isolating the problem. Unless detected by diagnostic programssuch 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 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? Does the failure symptom indicate a memory address problem, such as trying toaccess a protected area of memory? Is data corruption occurring? Backup data does not compare with original, orprogram executable code does not execute properly.If you believe that a VME controller board is causing data corruption, contact yourData General support service office as soon as possible.If the problem started after a system configuration change, return the system to itsoriginal configuration, if you can, until the failure has been properly evaluated byDGC support personnel.Bus Clear (BCLR*) ResponseBCLR* is driven by the arbiter to communicate to the current bus master, that ahigher priority request is pending; thus, the current bus master may release the busat the conclusion of the current transfer cycle.General Rules for Setting DTB PriorityNOTE: Before using this section, you must be familiar with the informationpresented 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 priorityof 3; priority will then be defined by the board positions (first slot has priorityover the second).
