[Simh] KDP Documentation

[Timothe Litt]

> I've got a couple of questions for you or anyone else:
> 1) The below document mentions the possibility of one or two DUPs 
> related to a single KMC. What tells the KMC which DUP it is to 
> exchange data with, and how does it know the DUP's bus address?
The KMC is passed the DUP's address by the OS in a base in command. (It 
must be in the IO page, so the high address bits don't need to be sent.)

; BASEIN:	BSEL2/	<LINE #>*400+3
;		BSEL6/	<DUP11 ADR>&017770

The OS knows - it probes the unibus or has the first DUP CSR hard-coded 
(varies withOS).

Then when other commands are sent to the KMC, they include the line 
number.  This is used to find the right DUP.

The KMC starts polling the DUP when Control-IN sets ENABLE.
> 2) You had mentioned previously that the host OS doesn't interact with 
> the DUP device except for a possible initial device probe testing for 
> NXM, and then writing zeros to the registers. What would happen if the 
> OS didn't find/see the DUP at all?
The OS checks for the DUP, and disables the line if it's not present 
(NXMs).  TOPS-20 writes zeros to the registers for some reason - 
probably paranoia.  I have a vague memory that modem status may be 
looked-at as well, but haven't tracked it down.

> 3) How many KMC/DUP devices would work on a given Unibus if there were 
> no power limitations (i.e. how many devices could the OS software 
> interact with)?
TOPS-20 is hard-coded at 1 KDP with 1 or 2 lines.  Expanding the number 
of lines would be easy; another KDP would be hard.

TOPS-10 is coded for more, but the configuration utility has limited 
it.  This would be a trivial patch - note that TOPS-10 monitors are 
compiled for each system.

The limits would be the line number field in the KDP commands, and 
Unibus mapping resources - each DUP takes at least 1 page - depends on 
the configured max message size.  UBA's are limited to 64 pages (each, 
but the KDP is known to be on UBA3).  But every DMA device uses some.

TOPS-10 also supports the DMR (up to 8) - which would be a better way to 
expand.

With two lines, typically a -10 or -20 would use one for DECnet - 
talking to a router.  The other for another protocol; ANF-10, IBM comm.  
Both happily used gateways to other networks hosted on VAX or 11s, or 
KLs.  Though we tried to use cheap 16/32-bit machines for the grunt work 
of pushing bits around.

> 4) Was there software support for talking to a bare DUP without a 
> related KMC in any PDP10 operating systems?
>
Not any DEC OS.  Can't speak for ITS, but I doubt it.
> 5) Was this KMC/DUP combination ever a supported device on PDP11 or 
> VAX systems? Thanks. - Mark
I don't have a reference handy, but I think it was supported at least on 
VAX and 11M.  They could have a mixture of stand-alone DUPs and DUPs 
controlled by KMCs.



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