UniBone: Linux-to-DEC-UNIBUS-bridge, year #1

Chris Zach cz at alembic.crystel.com
Wed Nov 20 10:37:14 CST 2019

> Well, I was expecting to have to do all of the work myself. There’s still the problem of the disk Unibus itself to solve - the disk UBA doesn’t terminate into a normal Unibus. It goes into the disk RH11 directly, and the bus is terminated on the far end of the RH11. I’d either have to buy another Unibus backplane to plug the Unibone into, or find a way to plug the cables from the UBA directly into the Unibone. This still leaves the issue of terminating the bus. The ideal scenario would be if the first slot of a RH11 (where the bus jumper comes in) can accommodate the (quad card) Unibone without issues, the rest of the RH11 boards can simply be pulled without breaking bus continuity, and the normal terminator in the far slot can be used. I haven’t looked at any prints or anything yet.

Right, there were two unibus ports on a 2020: The first one went to the 
RH11-C and was very odd in that "Hog Mode DMA" was enabled to allow the 
device to just stream data as much as it wanted to the controller. This 
would mean that other devices on the bus would time out and not have 
their interrupts serviced, but since the RH11 was the only thing it 
didn't matter (and I think this is why you could use RM03's instead of 
RM02's: The whole track could be read and buffered to the 2020's UBA 
controller in one shot. That would have to be programmed into the BBB 
software to ignore the 16 word DMA limits and go as fast as the drive 
can go).

So you would need two BA11's, one for the RH11C and one for the DZ11's 
and other unibus "stuff". *however* I seem to recall that the RH11C 
included a full length unibus slot after the boards, so maybe you could 
pull the RH11 boards and plug the BBB board into the end of the RH11C....

Gotta drag this stuff out and take a look. Oh and RD54's are *slow* 
compared to ESDI disks and controllers. Ouchies!


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