Data General AViiON Series, Клиентская документация

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Assigning VME Data Bus and Interrupt Priorities
E-8
014–001867
Alternate DTB Assignments
Note that the DTB priority assignments listed in Table E–2 also list, where
applicable, alternative lower fixed–priority levels that can be assigned to those
boards that will tolerate it. You may want to use lower priority settings in instances
where you want to give a competing board earlier access to the bus.
Table E–2 General Rules for VME TDB Priority Assignments
VME Default Setting Alternate Setting* Comments/
Device Bus Grant Priority Bus Grant Priority Notes
VSA 1 same Notes 2 & 4
VSC–3 3 same Note 1
VDA–255 3 2
VTC 3 2
VLC N/A N/A slave only
VLCi 3 2
VTRC 3 2
VFC 3 1
VAC16 3 2 Note 3
VDA–128 3 2 Note 3
VSCi/3 3 same Note 3
Notes
1. Within a level 3 group, place this board closest to the arbiter.
2. The positioning of VME DTB priority 1 boards depends on the function of the
attached devices. Some general rules for positioning of priority 1 boards are:
D
SCSI HBA with system disk is usually closest to the arbiter.
D
If there are 2 or more SCSI HBAs in the system the ones with slower devices
attached (tapes, optical disks, etc.) should be closer to the arbiter than those with
faster devices like Winchester disks. Slower SCSI devices should be on SCSI
channels separate from faster devices if at all possible.
3. Within its fixed priority group, this board must be farthest from the arbiter. When
more than one such board exist in a system, position the boards according to
their sequence in the table.
4. If you have empty slots between the arbiter and a HADA I IOP or between IOPs
that cannot be filled with DTB priority level 1 boards you may fill these slots with
other priority level boards as long as any VSAs in the system immediately follow
the last IOP and relative positioning of the other board agrees with the
positioning within the table.
* Use the alternate bus grant priority setting, if you believe that a system
performance problem exists due to VMEbus DTB priority
conflicts.