Q-bus tape drive problems
Dan Ts'o
dan at rna.UUCP
Sat Sep 21 02:49:23 AEST 1985
In article <8100003 at uiucdcs> goldberg at uiucdcs.Uiuc.ARPA writes:
>
>Is there anyone running 2.9 on a 22-bit Q-bus system using any 18-bit
>DMA devices? In particular, I have a TM-11 emulator that only does
>18-bit addressing. Rebooting every time I want to use the raw device
>is a royal pain. Suggestions or code greatfully appreciated. Thanks
>in advance for any assistance.
>
> Phil Goldberg
> 217-333-7620
> goldberg at Uiuc.ARPA
> ...!{ihnp4,convex,pur-ee}!uiucdcs!goldberg
I can think of two solutions.
1) Buy hardware. There exists Qbus maps which map the 18-bit Qbus
to the 22-bit Q-bus, analogous to a Unibus map. This of
courses assumes that the cost of the map (~$1500) doesn't
exceed a new controller for your tape (if you can get one,
is it formatted ?) Of course, other 18-bit devices would
then work as well, after modifying their drivers. Oh, and
you'll probably need a second Qbus chassis to serve as the
18-bit backplane.
Well, that solution isn't great unless you have a huge investment in
18-bit devices.
2) Try to lock each program that requires access to raw devices in
low-core (18-bit memory). This assumes you have some 18-bit memory
left (that the kernel is not using for its code, data, or buffers).
I don't remember, but I believe 2.9BSD still has the V7 lock() and
phys() call.
Using phys(), modify the kernel to allocate a buffer in 18-bit
space and modify your program, dd(1) for example, to use that
buffer, calling phys().
A better way, modify the lock() call, (a VERY simple mod) to
return the address where your program is locked. Then loop on
lock()/unlock() until your program is locked into 18-bit space.
You may require some other manipulation in between lock()'s to
insure that some swapping/memory shuffling is done to increase
your chances of being locked into 18-bit space.
We have used the last technique quite successfully. I can send
you the modified lock() system call.
I don't know of better solutions.
Cheers,
Dan Ts'o
Dept. Neurobiology
Rockefeller Univ.
1230 York Ave.
NY, NY 10021
212-570-7671
...cmcl2!rna!dan
rna!dan at cmcl2.arpa
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