Xref: news2.mv.net comp.os.msdos.djgpp:6017
From: Orbital <vazndain AT zveris>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Locking RAM for hardware interrupts
Date: Mon, 15 Jul 1996 18:43:57 +0300
Organization: LITNET
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Message-ID: <Pine.SOL.3.91.960715180219.9688B-100000@zveris>
References: <836949496 DOT 23711 DOT 0 AT abwillms DOT demon DOT co DOT uk> <31e3b1df DOT sandmann AT clio DOT rice DOT edu> <4s5dmj$bvj AT status DOT gen DOT nz>
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To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp



On Fri, 12 Jul 1996, Bruce Foley wrote:

> 
>                            If this is the case, then I imagine
> that any data (or code) associated with an ISR would cause
> a system crash if the interrupt was generated after the page had
> been swaped out (and was hence unavailable).  Is this right?
> 
  Absolutely. This is exactly why you need to lock it with DPMI function 
  0x600.

  Now something about the FAQ, so I suppose this goes to Eli:

  I haven't d/l'ed the FAQ 2.01, maybe it's already there, but anyway,
  here are some of my remarks:

  * The FAQ says [used to say?] that OS/2 Warp probably does not support
    FAT-DS. I am running OS/2 Warp revision 8.200 and it does. The FAQ
    does [did] not mention Windows NT, which definitely does not support
    FAT-DS, though. Also, the FAQ makes [used to make] the FAT-DS approach
    look kinda scary (at least to me). It is clear, that every single
    Watcom/DOS4GW application uses it (not sure, but I think Borland 4.5+
    32 bit DOS apps do as well) and nobody seems to care much.

  * The FAQ could [does?] have a hint to prevent GNU Make from crashing
    under OS/2 Warp. The hint to set DPMI_DOS_API to ENABLED instead of
    AUTO in DOS Settings for the session. DPMI_MEMORY_LIMIT is also nice
    to experiment with.

  * Now, I'm not sure about this one, but I think I somewhere saw the FAQ
    [or other docs] say in the what's-new section, that starting from some
    beta of V2, dos selector limit was set to 4GB (fat, eh?). However, when
    I checked the sources, I saw it being set to 16MB. What did I miss?


  Now, I would like to continue with the FAT-DS thread. If the problem was
  memory protection and not the NT and Linux DOS-box compatibility, then
  you could just enable near pointers, do your stuff and then disable them.
  However, this is slow, because __djgpp_nearptr.. functions issue DPMI calls
  etc. I found a cool workaround for that:
  
  [1] Allocate an alias to your data descriptor and set its limit to 4GB.
  [2] When you need near pointers, load ds and es with the alias.
  [3] When done reload ds and es with the original selector.

  Voila. Steps [2] and [3] are much faster than __djgpp_nearptr.. calls. To
  be more precise, there is no need to allocate the alias, it's already 
  there, stored in __djgpp_ds_alias variable. Just fatten it and that's it.
  There is also no need to store the original one, as it is stored in a
  variable __djgpp_app_DS. Both of them are unsigned short ints. Now, a
  nearptr_enavble() would look like this:
  
    asm volatile ("mov __djgpp_dos_alias,%es; mov __djgpp_dos_alias,%ds");

  and nearptr_disable() would be:

    asm volatile ("mov __djgpp_app_DS,%es; mov __djgpp_app_DS,%ds");

  Plus it would take a single call to
 
    __dpmi_set_selector_limit(__djgpp_ds_alias, -1);

  somewhere at startup. Hope someone finds this useful. Tell me if I'm
  wrong somewhere as I have not tested it myself.

  Plus one question to everybody:

  ? is it worth installing Linux on a 486DX4-100 with 16MB RAM and 
  ? >NO INTERNET ACCESS< ? I used to think UNIX was mostly usefull to
  ? access the internet, but indeed, are people using Linux as a Desktop OS?
  ? What attracts me the most is gcc in its native [at least more native
  ? than DOS] environment. Is X programming difficult compared to MS-Win?
  ? Man, I could write X demos and recompile and run them on Suns at my
  ? university, is that right? How's the speed and stabilty of Linux? 
  ? What about the HD space? Is it possible to uninstall all the internet
  ? stuff? What about sound and video cards? Are many of them supported?

  Enough for now. You must be pretty cool if you managed to read up to here.
  Man, this *is* a long message. Sorry if I didn't write anything interesting. 
  
  
  Orbital