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Re: QBUS Prototyping

Started bykoehler@eisner.nospam.encompasserve.org (Bob Koehler)
First post2011-04-18 07:56 -0500
Last post2011-04-18 20:36 -0700
Articles 9 — 3 participants

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  Re: QBUS Prototyping koehler@eisner.nospam.encompasserve.org (Bob Koehler) - 2011-04-18 07:56 -0500
    Re: QBUS Prototyping Johnny Billquist <bqt@softjar.se> - 2011-04-18 08:07 -0700
      Re: QBUS Prototyping moroney@world.std.spaamtrap.com (Michael Moroney) - 2011-04-18 17:26 +0000
        Re: QBUS Prototyping koehler@eisner.nospam.encompasserve.org (Bob Koehler) - 2011-04-18 12:53 -0500
        Re: QBUS Prototyping Johnny Billquist <bqt@softjar.se> - 2011-04-18 20:35 -0700
          Re: QBUS Prototyping moroney@world.std.spaamtrap.com (Michael Moroney) - 2011-04-19 15:34 +0000
            Re: QBUS Prototyping Johnny Billquist <bqt@softjar.se> - 2011-04-19 09:47 -0700
      Re: QBUS Prototyping koehler@eisner.nospam.encompasserve.org (Bob Koehler) - 2011-04-18 12:49 -0500
        Re: QBUS Prototyping Johnny Billquist <bqt@softjar.se> - 2011-04-18 20:36 -0700

#226 — Re: QBUS Prototyping

Fromkoehler@eisner.nospam.encompasserve.org (Bob Koehler)
Date2011-04-18 07:56 -0500
SubjectRe: QBUS Prototyping
Message-ID<WgK6B$GCJWnT@eisner.encompasserve.org>
In article <hr19ad$m2m$1@Iltempo.Update.UU.SE>, Johnny Billquist <bqt@softjar.se> writes:
> 
> (Oh, and a VAX is not a PDP... :-)

   That's right.  No VAX ever implemented the MARK instruction.  Now
   can you find a PDP-11 programmer who actually used it?

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#229

FromJohnny Billquist <bqt@softjar.se>
Date2011-04-18 08:07 -0700
Message-ID<iohk2q$kmg$2@Iltempo.Update.UU.SE>
In reply to#226
On 2011-04-18 05:56, Bob Koehler wrote:
> In article<hr19ad$m2m$1@Iltempo.Update.UU.SE>, Johnny Billquist<bqt@softjar.se>  writes:
>>
>> (Oh, and a VAX is not a PDP... :-)
>
>     That's right.  No VAX ever implemented the MARK instruction.  Now
>     can you find a PDP-11 programmer who actually used it?

I used it.
But only to test how to, and then decided "never more". :-)

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt@softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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#231

Frommoroney@world.std.spaamtrap.com (Michael Moroney)
Date2011-04-18 17:26 +0000
Message-ID<iohs8j$ha6$1@pcls6.std.com>
In reply to#229
Johnny Billquist <bqt@softjar.se> writes:

>On 2011-04-18 05:56, Bob Koehler wrote:
>> In article<hr19ad$m2m$1@Iltempo.Update.UU.SE>, Johnny Billquist<bqt@softjar.se>  writes:
>>>
>>> (Oh, and a VAX is not a PDP... :-)
>>
>>     That's right.  No VAX ever implemented the MARK instruction.  Now
>>     can you find a PDP-11 programmer who actually used it?

>I used it.
>But only to test how to, and then decided "never more". :-)

I'm guessing that instruction was developed for some compiler(s) which had
some bizarre linkages for subroutines, and very few, if any, assembly
language programmers ever used it, beyond trying to figure out what to do
with it.

(next question, which compiler(s) used it?)

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#234

Fromkoehler@eisner.nospam.encompasserve.org (Bob Koehler)
Date2011-04-18 12:53 -0500
Message-ID<i04h6QgHCxQo@eisner.encompasserve.org>
In reply to#231
In article <iohs8j$ha6$1@pcls6.std.com>, moroney@world.std.spaamtrap.com (Michael Moroney) writes:
> 
> I'm guessing that instruction was developed for some compiler(s) which had
> some bizarre linkages for subroutines, and very few, if any, assembly
> language programmers ever used it, beyond trying to figure out what to do
> with it.

   I've worked with non-stack oriented systems that passed their
   arguments via memory resident linkages.  MARK looked to me like an
   attempt to do something like that, but in a way that it actually
   had to use a stack.

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#236

FromJohnny Billquist <bqt@softjar.se>
Date2011-04-18 20:35 -0700
Message-ID<ioivtk$4ss$1@Iltempo.Update.UU.SE>
In reply to#231
On 2011-04-18 10:26, Michael Moroney wrote:
> Johnny Billquist<bqt@softjar.se>  writes:
>
>> On 2011-04-18 05:56, Bob Koehler wrote:
>>> In article<hr19ad$m2m$1@Iltempo.Update.UU.SE>, Johnny Billquist<bqt@softjar.se>   writes:
>>>>
>>>> (Oh, and a VAX is not a PDP... :-)
>>>
>>>      That's right.  No VAX ever implemented the MARK instruction.  Now
>>>      can you find a PDP-11 programmer who actually used it?
>
>> I used it.
>> But only to test how to, and then decided "never more". :-)
>
> I'm guessing that instruction was developed for some compiler(s) which had
> some bizarre linkages for subroutines, and very few, if any, assembly
> language programmers ever used it, beyond trying to figure out what to do
> with it.

One rumour has it that it was developed in order to extend some patent 
or something.

Another would be that they were just crazy.

I've not seen a single compiler use the subroutine linkage that 
explicitly makes the MARK instruction meaningful, and besides. It is not 
usable if you have split I/D space.

> (next question, which compiler(s) used it?)

I have no idea.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt@softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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#243

Frommoroney@world.std.spaamtrap.com (Michael Moroney)
Date2011-04-19 15:34 +0000
Message-ID<ioka2m$bee$1@pcls6.std.com>
In reply to#236
Johnny Billquist <bqt@softjar.se> writes:

>One rumour has it that it was developed in order to extend some patent 
>or something.

I heard the same little birdie, and it certainly makes sense, to make the
instruction set unique.  Someone could probably find another processor or
processors that essentially implement each of the other PDP-11
instructions.  Kind of like deliberate errors added to copyrighted maps.

>Another would be that they were just crazy.

That certainly would have helped!

>I've not seen a single compiler use the subroutine linkage that 
>explicitly makes the MARK instruction meaningful, and besides. It is not 
>usable if you have split I/D space.

I won't claim there is one, esp. if it doesn't work with split I/D space.

>> (next question, which compiler(s) used it?)

>I have no idea.

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#247

FromJohnny Billquist <bqt@softjar.se>
Date2011-04-19 09:47 -0700
Message-ID<iokeab$ja3$1@Iltempo.Update.UU.SE>
In reply to#243
On 2011-04-19 08:34, Michael Moroney wrote:
> Johnny Billquist<bqt@softjar.se>  writes:
>
>> One rumour has it that it was developed in order to extend some patent
>> or something.
>
> I heard the same little birdie, and it certainly makes sense, to make the
> instruction set unique.  Someone could probably find another processor or
> processors that essentially implement each of the other PDP-11
> instructions.  Kind of like deliberate errors added to copyrighted maps.

Yeah.

>> Another would be that they were just crazy.
>
> That certainly would have helped!

:-)

>> I've not seen a single compiler use the subroutine linkage that
>> explicitly makes the MARK instruction meaningful, and besides. It is not
>> usable if you have split I/D space.
>
> I won't claim there is one, esp. if it doesn't work with split I/D space.

And it won't. The idea with the MARK instruction is that it is pushed on 
the stack. At subroutine return, you are then supposed to jump to where 
the stack pointer points, and execute there, which is on the stack. This 
will clean up the stack, and restore PC.
So stack needs to be in I-space. But for all other purposes stack is in 
D-space. So in short, stack needs to be in both I-space and D-space for 
the MARK instruction to work.
So it can't be split. Pretty useless, if you ask me.

And all just for making the cleaning of the stack from arguments to the 
function a little more streamlined. Having just an ADD #n,SP works just 
as fine, and do work with split I/D-space. :-)
The difference being that the caller needs to clean the stack explicitly 
after a call, while with MARK, the caller push the MARK before calling, 
and the stack is cleaned as a part of the return.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt@softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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#232

Fromkoehler@eisner.nospam.encompasserve.org (Bob Koehler)
Date2011-04-18 12:49 -0500
Message-ID<ozUAgxVPcJz7@eisner.encompasserve.org>
In reply to#229
In article <iohk2q$kmg$2@Iltempo.Update.UU.SE>, Johnny Billquist <bqt@softjar.se> writes:
> 
> I used it.
> But only to test how to, and then decided "never more". :-)

   Yes, I did that once.  It was quite painfull.  It looked to me
   like whoever designed it didn't actually get what he intended.

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#237

FromJohnny Billquist <bqt@softjar.se>
Date2011-04-18 20:36 -0700
Message-ID<ioivvr$4ss$2@Iltempo.Update.UU.SE>
In reply to#232
On 2011-04-18 10:49, Bob Koehler wrote:
> In article<iohk2q$kmg$2@Iltempo.Update.UU.SE>, Johnny Billquist<bqt@softjar.se>  writes:
>>
>> I used it.
>> But only to test how to, and then decided "never more". :-)
>
>     Yes, I did that once.  It was quite painfull.  It looked to me
>     like whoever designed it didn't actually get what he intended.

Yes. That sounds like a reasonable guess.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt@softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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