From: korpela AT islay DOT ssl DOT berkeley DOT edu (Eric J. Korpela)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: How do I disable disable Virtual memory??
Date: 30 Sep 1996 23:21:52 GMT
Organization: Cal Berkeley-- Space Sciences Lab
Lines: 69
Message-ID: <52pkmg$959@agate.berkeley.edu>
References: <52kebp$3l4 AT mn5 DOT swip DOT net>
NNTP-Posting-Host: islay.ssl.berkeley.edu
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

In article <52kebp$3l4 AT mn5 DOT swip DOT net>,
Peter Nordlander  <peter DOT nordlander AT mbox2 DOT swipnet DOT se> wrote:
>Hi!
>
>I've just coded a keyboard interrupt in DJGPP 2.0. The problem is that
>the handler is written in C (not in asm) so i can't lock the wrapper and
>messages like "Page fault" appears on the screen. 
>I've heard that to solve this problem I could disable Virtual memory so 
>that my handler wont page.

The best way to lock a handler is with the __dpmi_lock_linear_region()
when you install the handler.  That way you still get the benefits
of paging for the rest of the program.  The other alternative is to
use "_crt0_startup_flags |= _CRT0_FLAG_LOCK_MEMORY" which locks all
memory.

struct {
  char data_used_by_handler[DATASIZE];
} lock_me;

_go32_dpmi_seginfo old_seg_info;
_go32_dpmi_seginfo handler_seg_info;

void handler()
{
/*  do stuff with data_used_by_handler */
}

void end_of_handler()  /* must be in same object file as handler() */
{
}
  
__dpmi_meminfo data_info, handler_info;

int install_handler()
{
  data_info.address=&lock_me;
  data_info.size=sizeof(lock_me);
  handler_info.address=handler;
  handler_info.size=(unsigned long)(end_of_handler-handler);
  handler_seg_info.pm_offset=handler;
  handler_seg_info.pm_selector=_go32_my_cs;
  return (
    (old_seg_info.pm_offset != NULL)  /* don't do it twice */
    __dpmi_lock_linear_region(&data_info) ||
    __dpmi_lock_linear_region(&handler_info) ||
    _go32_dpmi_allocate_iret_wrapper(&handler_seg_info) ||
    _go32_dpmi_get_protected_mode_interrupt_vector(VECTOR,old_seg_info) ||
    _go32_dpmi_set_protected_mode_interrupt_vector(VECTOR,handler_seg_info)
  );
}
  
int uninstall_handler()
{
  return (
      _go32_dpmi_set_protected_mode_interrupt_vector(VECTOR,old_seg_info) ||
      _go32_dpmi_free_iret_wrapper(&(lock_me.handler_seg_info)) ||
      __dpmi_unlock_linear_region(&handler_info) ||
      __dpmi_unlock_linear_region(&data_info) 
  );
}
  
  
Eric
-- 
Eric Korpela                        |  An object at rest can never be
korpela AT ssl DOT berkeley DOT edu            |  stopped.
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