Unibus disk controller with modern storage

Paul Koning paulkoning at comcast.net
Thu Oct 20 15:27:42 CDT 2016

> On Oct 20, 2016, at 4:14 PM, Ethan Dicks <ethan.dicks at gmail.com> wrote:
> On Wed, Oct 19, 2016 at 7:46 PM, Paul Koning <paulkoning at comcast.net> wrote:
>> Actually, Unibus has very straightforward timing.  It certainly should be a breeze with an FPGA, but the original designs (nicely spelled out in the back of the early Peripherals Handbooks, or later on in the Unibus Handbook) take just a handful of MSI ICs.
> Then there's the interminable wrestling with "what driver ICs to use".
> I have an abundance of the real thing (DC013 and NS8641, because I
> used to make a peripheral), but modern equivalents all fall short in
> one way or another.  You _can_ get away with a variety of
> substitutions, but the question then becomes when those compromises
> sum up to bite you.

I would treat this as an analog problem, putting some op amps and comparators to work.  It doesn't seem to rise to the level where D/A devices are needed.  :-)

>> Yes, a non-MSCP disk would be a good choice.  I'd suggest the Massbus series, they are just about as simple as anything and that's where you find the largest capacities short of MSCP devices.
> With widespread driver support (because who wants to write a wad of
> drivers for different operating systems and different _versions_ of
> operating systems - VMS4 vs VMS5 w/SMP anyone?  Done that already!).
> The worst thing about rolling your own  controller is needing to write
> all the drivers, thus the interest in something universal, like MSCP -
> the interface to the bus, the register model, is all set and somewhat
> clear.  Implementation details are invisible to the bus or OS.  OTOH,
> rolling your own MSCP device is hardly a starter project.

Right.  I meant an existing non-MSCP non-RL device.  Most other disks have extremely straightforward register command sets; RK05, RP06, the details differ but the general approach is very easy.

Any non-DEC disk would be a problem.  Writing drivers is a pain if it's even possible; for some operating systems like RSTS it flat out isn't supported.


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