Groups > comp.os.msdos.programmer > #1402

Re: detecting emulation or console windows

From	"James Harris" <james.harris.1@gmail.com>
Newsgroups	alt.os.development, comp.os.msdos.programmer, alt.lang.asm
Subject	Re: detecting emulation or console windows
Date	2014-06-04 07:55 +0100
Organization	A noiseless patient Spider
Message-ID	<lmmfsr$f7n$1@dont-email.me> (permalink)
References	(7 earlier) <op.xgtf1zk06zenlw@localhost> <lmhduh$uji$1@dont-email.me> <op.xgtw0lnh6zenlw@localhost> <lmi7cc$ilr$1@dont-email.me> <op.xguoost76zenlw@localhost>

Cross-posted to 3 groups.

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"Rod Pemberton" <dont_use_email@xnothavet.cqm> wrote in message 
news:op.xguoost76zenlw@localhost...
> On Mon, 02 Jun 2014 12:05:34 -0400, James Harris 
> <james.harris.1@gmail.com> wrote:
>> "Rod Pemberton" <dont_use_email@xnothavet.cqm> wrote in message
>> news:op.xgtw0lnh6zenlw@localhost...
>
>>> I have a whole bunch of DOS .com's which
>>> enable and disable A20.  In DOS, you have to
>>> boot clean, i.e., no XMS memory manager to
>>> correctly detect and use A20.  XMS memory managers
>>> emulate A20.
>>
>> You mean they enable it and then program segment tables
>> to mimic wrapping as needed?
>
> I'm not sure what XMS does with A20.  It's emulated somehow.
> I'd have to recheck, but I think XMS wouldn't let you enable
> or disable A20 via the standard methods.

AFAICT XMS provides an API for managing memory. It provides A20 management 
calls but I cannot see how it can trap and emulate A20 changes. I say that 
because XMS was a spec from the early days of long ago, wasn't it? I don't 
think PCs had any virtualisation support then. Real-mode code that changed 
A20 would run as privileged and so I cannot see how such could trap to 
anything. Nor could it prevent access to the keyboard controller so I cannot 
see how XMS could prevent a program from changing A20.

...

>>> AIUI, the Int instruction should force memory coherency
>>> and/or cache flush etc to ensure that the memory wrap or
>>> unwrap is in effect prior to generating the interrupt.
>>
>> Is that needed?
>
> It's done.  It's been done.  It works.

Putting a NOP in a piece of code also "works" but its presence might be 
misleading and unnecessary and nothing to do with whether the piece of code 
works or not!

> Codewise, it looks clean-er...
>

...

> P.S.  Opera has an option which says it's supposed to be wrapping lines 
> for Usenet so I'm sending this extra long one to see what happens ...

Haven't checked in any detail but the posts do seem easier to read.

James

Thread

detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-31 18:31 -0400
  Re: detecting emulation or console windows Ross Ridge <rridge@csclub.uwaterloo.ca> - 2014-05-31 19:59 -0400
    Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-31 20:54 -0400
      Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-05-31 21:43 -0400
        Re: detecting emulation or console windows "James Harris" <james.harris.1@gmail.com> - 2014-06-01 22:48 +0100
          Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-02 00:46 -0400
            Re: detecting emulation or console windows "James Harris" <james.harris.1@gmail.com> - 2014-06-02 06:15 +0100
              Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-02 03:21 -0400
                Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-02 03:32 -0400
                Re: detecting emulation or console windows "James Harris" <james.harris.1@gmail.com> - 2014-06-02 09:51 +0100
                Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-02 09:27 -0400
                Re: detecting emulation or console windows "James Harris" <james.harris.1@gmail.com> - 2014-06-02 17:05 +0100
                Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-02 19:25 -0400
                Re: detecting emulation or console windows "James Harris" <james.harris.1@gmail.com> - 2014-06-04 07:55 +0100
                Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-04 03:20 -0400
      Re: detecting emulation or console windows Ross Ridge <rridge@csclub.uwaterloo.ca> - 2014-06-01 14:03 -0400
        Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-02 00:53 -0400
          Re: detecting emulation or console windows Ross Ridge <rridge@csclub.uwaterloo.ca> - 2014-06-02 15:55 -0400
            Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-02 19:27 -0400
              Re: detecting emulation or console windows Ross Ridge <rridge@csclub.uwaterloo.ca> - 2014-06-03 17:00 -0400
  Re: detecting emulation or console windows Sjouke Burry <burrynulnulfour@ppllaanneett.nnll> - 2014-06-01 06:25 +0200
    Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-01 02:50 -0400
  Re: detecting emulation or console windows "James Harris" <james.harris.1@gmail.com> - 2014-06-01 07:53 +0100
    Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-01 04:53 -0400
      Re: detecting emulation or console windows "James Harris" <james.harris.1@gmail.com> - 2014-06-01 20:57 +0100
        Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-02 00:48 -0400
      Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-02 03:20 -0400
  Re: detecting emulation or console windows JJ <duh@nah.meh> - 2014-06-02 03:43 +0700
    Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-02 00:34 -0400
    Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-03 07:06 -0400
      Re: detecting emulation or console windows JJ <duh@nah.meh> - 2014-06-03 20:25 +0700
  Re: detecting emulation or console windows "wolfgang kern" <nowhere@never.at> - 2014-06-03 20:52 +0200
  Re: detecting emulation or console windows "James Harris" <james.harris.1@gmail.com> - 2014-06-03 22:59 +0100
    Re: detecting emulation or console windows CN <qmbmnp3799@pacbell.net> - 2014-06-03 18:39 -0700
      Re: detecting emulation or console windows "James Harris" <james.harris.1@gmail.com> - 2014-06-04 07:06 +0100
        Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-04 03:07 -0400
          Re: detecting emulation or console windows "James Harris" <james.harris.1@gmail.com> - 2014-06-04 09:16 +0100
  Re: detecting emulation or console windows "James Harris" <james.harris.1@gmail.com> - 2014-06-03 23:00 +0100
  Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-06-10 17:37 -0400
    Re: detecting emulation or console windows Wildman <best_lay@yahoo.com> - 2014-06-11 00:37 +0000
      Re: detecting emulation or console windows "Rod Pemberton" <dont_use_email@xnothavet.cqm> - 2014-07-27 12:11 -0400

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