MSCP - was Re: Unibus / Qbus

allison ajp166 at
Mon Oct 24 11:34:26 CDT 2016

On 10/24/16 8:51 AM, Paul Koning wrote:
>> On Oct 24, 2016, at 7:39 AM, allison <ajp166 at> wrote:
>> On 10/22/16 6:05 PM, Toby Thain wrote:
>>> On 2016-10-22 4:08 PM, allison wrote:
>>>> ...
>>>> FYI I have never heard of any one recreating the RQDX1/2/3 software
>>>> protocol MSCP
>>>> as it was nontrivial, proprietary, and copyrighted.
>>> It's been implemented in simh, afaik. Its reputation is a little more imposing than the reality.
>>> ...
>> That may be so but putting it on a board to accept a IDE drive is far more useful to us that run hardware.
>> Why IDE, It can use CF and I also have a large supply of drives from 20-512mb.   Fortunately I have a
>> large supply of MFM drives and two SCSI controllers for the larger supply of SCSI drives.  However, I
>> feel I'm the exception and many Qbus users are not so fortunate.
>> Where is the source code to for that? That is the drive side of that.
> There's pdp11_rq.c.  If you were to do a bus interface with microprocessor behind it for the protocol work, that code could be adapted for the job.  And that would be the obvious way to build an MSCP controller -- that's how MSCP was designed to be implemented and how it was done in DEC's controllers.  A BeagleBone Black or the like would be more than ample for the job, given that early implementations such as the UDA50 were done with 2901 bitslice engines (and very odd looking microcode).
> 	paul
And the RQDX1/2/3 used T11 for the job so its not that intense save for 
The other part of it is much of the code is likely the interface to the 
MFM disk and thats
speed intensive and likely more hardware than software.

I'll have to scratch at the code and see.



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