<Isn't it harder than just writing the RLV11 device driver?  After
<all, you have to make sure that *nothing* else in the OS attempts

I'll bet it does.  I did a PDP-11/23b setup with 1mb Q-bus ram and a 
RLV11 and it crashes with rt11 if I try to address the RL02.  As a 
check I put the RLV12 back in and it operated normally it also worked 
if I cut the total ram to 256k with the RLV11.

The problem is not the 18bit dma limitation as that can be handled as a
local buffer problem is the device register showing up all over the place.

<This will probably make Q-bus graphics support especially difficult, as y
<have to be sure that none of your graphics buffers are over 256k long
<and that they are all aligned properly.

It would kill you.

<Support for less-brain-damaged 18-bit DMA devices is much more
<straightforward - for example, for a RXV21 all you need is a "bounce-buff
<in the lower 256 k for DMA's to go to/from.  This is much simpler than
<RLV11 support.

The RXV21 is sane as is RLV12 as I've put them is VMS powered vaxen in the 
past with zero trouble.

Supporting RLV11 would be a major problem.  This also ignores the 
problem of putting a RLV11 in a vax Q22 backplane is not possible due 
to required CD connect (cannot use the memory slots).  I'd save the RLV11 
for a Q18 11/23 or other Q-bus PDP11 with 256k or less ram.  It's one of 
only a few devices that are not Q22 complient.  For VAX that is a must.


Allison