Re: [Simh] PDP-11 MARK
It would have been nice of you, Dave Porter, to include a link to the source of inspiration for your question: https://retrocomputing.stackexchange.com/q/7056/4025 Leo On Wed, Aug 1, 2018 at 5:26 PM, dave porter wrote: > Not really a simh question, but this might be an appropriate > bunch of people. What actually used MARK on PDP-11? > > I think I recall that some Fortran system (F4P?) used it, > but that's a vague feeling at most. > > Certainly as a Macro-11 kernel-mode weenie, I never > felt the need. > > > ___ > Simh mailing list > Simh@trailing-edge.com > http://mailman.trailing-edge.com/mailman/listinfo/simh ___ Simh mailing list Simh@trailing-edge.com http://mailman.trailing-edge.com/mailman/listinfo/simh
Re: [Simh] PDP-11 MARK
On 2018-08-02 15:12, Paul Koning wrote: On Aug 1, 2018, at 9:06 PM, Johnny Billquist wrote: On 2018-08-02 02:26, dave porter wrote: Not really a simh question, but this might be an appropriate bunch of people. What actually used MARK on PDP-11? I think I recall that some Fortran system (F4P?) used it, but that's a vague feeling at most. Certainly as a Macro-11 kernel-mode weenie, I never felt the need. As far as I know, nothing used MARK. I believe that is correct. It's ugly in that it requires that I-space and D-space overlap, at least for the stack, for it to work. And you have to execute the stack, which is a weird thing for programs to do in any case. Yes. I once heard a rumor that DEC only came up with it to extend some copyright or patent a few more years, but I'm not sure there is much truth in that. I've had some discussions around DEC with people who knew about MARK, but that particular rumor does not sound at all familiar. Like I said, I'm not sure I put much worth into it. I don't recall the exact conspiracy theory behind it, but essentially went along the path of this extension allowed DEC to put a new patent in, which extended the protection of the architecture for another few years. But it might also have been more generally related to the EIS. Can't remember for sure, and I have no recollection where I read it. Anyway, it was an attempt at having a return mechanism for routines that cleaned up the stack, in a time where you did not have a frame pointer. Yes. But the cost (time and space) of pushing the right MARK onto the stack is likely comparable to the cost of simply cleaning up the stack explicitly, without any of the mess associated with that instruction. The one advantage of MARK is that you don't have to know how much stuff have been put on the stack in the local routine before leaving. All that is implicitly cleaned up through the use of the MARK. But it's definitely not worth it, since you have to sacrifice quite a lot of potential separate I-space for it, along with forcing you to use R5 a bit special as well. Johnny -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: b...@softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol ___ Simh mailing list Simh@trailing-edge.com http://mailman.trailing-edge.com/mailman/listinfo/simh
Re: [Simh] PDP-11 MARK
> On Aug 2, 2018, at 4:25 PM, Bob Eager wrote: > > On Thu, 2 Aug 2018 22:00:05 +0200 > Rhialto wrote: > > > Most overviews of the instruction set do not even explain what it > > does. I only found it in the older ones, such as in the PDP 11-40 > > Processor Handbook (page 4-61, pdf page 107). > > I remember considering using it when writing a compiler for the 11. In > the end I decided it was more trouble than it was worth. I came to the same conclusion when I was looking at it the other day, while working on the gcc back-end for pdp11. paul ___ Simh mailing list Simh@trailing-edge.com http://mailman.trailing-edge.com/mailman/listinfo/simh
Re: [Simh] PDP-11 MARK
-BEGIN PGP SIGNED MESSAGE- Hash: SHA256 On Thu, 2 Aug 2018 22:00:05 +0200 Rhialto wrote: > Most overviews of the instruction set do not even explain what it > does. I only found it in the older ones, such as in the PDP 11-40 > Processor Handbook (page 4-61, pdf page 107). I remember considering using it when writing a compiler for the 11. In the end I decided it was more trouble than it was worth. -BEGIN PGP SIGNATURE- iQEzBAEBCAAdFiEEVgdI2KeVldPAhUYaKBdf2az8e6gFAltjaMsACgkQKBdf2az8 e6iYggf7BNhIhzvnAz6b+XdUJuPr10IhT6XRiBjbQ/WO3zJaFclPel0hHxgVguOf R08RpGJKU1lzsDcSj8R+0J0kgTnhOgqU3GttOXqXg/e4wJtAGS5a20ZGqHil7fVs SP1TGamphqoOJ3wbTJkD41S1xlrznCVkDcojR3r00CyCZGHY61sE2Q4ZE6iS1QmH v9HXa6GfnlvLu4VWlAde8oFG3cLPQP7Eq/bYPeOSMMivjFmg6j8LOR+A8KyA0Wdx 1FrA/oFCQswjlQD54LR+8bwcfRMjGcBmHgDyVJxsDns+6Wc6uZQiNIiRb1JSgZqe wcCs52MnUP7Sj0A8VxCKUYJTwpJDyQ== =UVIP -END PGP SIGNATURE- ___ Simh mailing list Simh@trailing-edge.com http://mailman.trailing-edge.com/mailman/listinfo/simh
Re: [Simh] PDP-11 MARK
On Thu 02 Aug 2018 at 09:12:16 -0400, Paul Koning wrote: > > I believe that is correct. Most overviews of the instruction set do not even explain what it does. I only found it in the older ones, such as in the PDP 11-40 Processor Handbook (page 4-61, pdf page 107). -Olaf. -- ___ Olaf 'Rhialto' Seibert -- Wayland: Those who don't understand X \X/ rhialto/at/falu.nl -- are condemned to reinvent it. Poorly. signature.asc Description: PGP signature ___ Simh mailing list Simh@trailing-edge.com http://mailman.trailing-edge.com/mailman/listinfo/simh
Re: [Simh] PDP-11 MARK
On 2018-08-02 02:26, dave porter wrote: Not really a simh question, but this might be an appropriate bunch of people. What actually used MARK on PDP-11? I think I recall that some Fortran system (F4P?) used it, but that's a vague feeling at most. Certainly as a Macro-11 kernel-mode weenie, I never felt the need. As far as I know, nothing used MARK. It's ugly in that it requires that I-space and D-space overlap, at least for the stack, for it to work. I once heard a rumor that DEC only came up with it to extend some copyright or patent a few more years, but I'm not sure there is much truth in that. Anyway, it was an attempt at having a return mechanism for routines that cleaned up the stack, in a time where you did not have a frame pointer. Johnny -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: b...@softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol ___ Simh mailing list Simh@trailing-edge.com http://mailman.trailing-edge.com/mailman/listinfo/simh
[Simh] PDP-11 MARK
Not really a simh question, but this might be an appropriate bunch of people. What actually used MARK on PDP-11? I think I recall that some Fortran system (F4P?) used it, but that's a vague feeling at most. Certainly as a Macro-11 kernel-mode weenie, I never felt the need. ___ Simh mailing list Simh@trailing-edge.com http://mailman.trailing-edge.com/mailman/listinfo/simh
