[Simh] Questions regarding future simulator development

[Johnny Billquist]

On 2013-04-11 04:37, Mark Pizzolato - Info Comm wrote:
> On Wednesday, April 10, 2013 at 5:13 PM, Christian Gauger-Cosgrove wrote:
>> Hello Mark,
>>
>> On 10 April 2013 13:37, Mark Pizzolato - Info Comm <Mark at infocomm.com>
>> wrote:
>>> Once again, anything is possible, but this would be a significant amount of
>> work.   If there was some formal documentation available which described
>> the RS03 and RS04 disks, then adding them to the pdp11_rq.c code would
>> probably not be too hard.  Looking in the 'usual places' on bitsavers.org
>> doesn't provide any information on these disk devices though.
>>>
>> Well it would be to the pdp11_rp.c code, but either way, they're just another
>> form of MASSBUS disk, and in my quick browse through the pdp11_rp.c
>> code, it looks likes like the various drives under its purview are only defined
>> as their geometries. So to add the RS03 and RS04, all that would be needed
>> to be added -- in my quick glance at the code, would only require entering
>> the proper geometry for the devices.
>
> They are just another form of MASSBUS disk, BUT do they share register functionality with the existing RP/RM disks?  A RS03 and RS04 document would describe these details.  The geometry is certainly necessary, but it is not complete.  As far as I know, the RS03/RS04 were never supported on VMS. So I don't have access to driver source listings to 1) analyze what the host software is expecting and 2) to actually test things out.

RM and RP disks do not have the same register layout on the Massbus. 
However, the difference is just one or two registers, and those are 
related to error handling if I remember right. So an emulation can 
pretty much pretend they are the same.
(And to make things even more weird, the RP07 have the same register 
layout as the RM drives...)

In RSX, the RP drives use the DB: device, while RM drives (and the RP07) 
uses the DR: device.

And correct, RS drives were never supported in VMS. Neither was the 
ML11, which is a ram disk for the massbus.
And in RSX, RS03/RS04 is DS: while ML11 is EM:

RSX always ships with sources, and older versions of RSX is definitely 
available for hobbyist use, so sources to device drivers are available.

>> There is only one set of drives that isn't implemented in SIMH at present, is
>> the pre-MASSBUS RP drives (on the actual RP11 controller, so RP01, RP02 and
>> RP03). But I don't think much if any still extant software even supports the
>> RP0[1:3].
>
> Given that, I'm not too worried.  Once again, If you can come up with detailed device documentation we can look at what it will take to add this functionality into simh.  Maybe someone has visibility into a PDP11 OS device driver source for these devices and can confirm at least that the driver is shared between either the RP disks or the RM disks.  If so, then maybe all we're talking about is adding a different drive type.  If, the register set/driver is different, then we'll need more detail....

The RP01/02/03 drives are not massbus drives. They have their own 
controller, called RP11, which was a whole cabinet of flip chips and 
blinkenlights.

Thus, it isn't meaningful to look at newer RP drives when we talk about 
these. Sources to the device drivers are (as usual) available in RSX. In 
this case it is the DP: driver.

>> Of course it is possible to "misconfigure" a system, But I know in my own
>> case, I try to keep any system configurations limited to what was actually
>> possible (with the occasional waiver, e.g. having the RP drive series plus its
>> associated RH controller on a QBUS system with the justification of
>> "somewhere there is a third party board that let's you put a CDC 9766 on a
>> QBUS box".
>
> These choices existed, but when the 3rd party Qbus controller business really blossomed in the mid 80's the MSCP devices were already well established and using such a controller let you use the natural size of whatever SMD disk you connected to them.

True.
But then again, there was also the (late) "RM06" massbus disk, which is 
variable size. Not made by DEC, but by Shelby.

Someone also mentioned dual-ported disks. That could be fun and cool as 
well, although I wouldn't expect there to be much performance gain to be 
had today.

	Johnny