From: "Anthony.Appleyard" <MCLSSAA2 AT fs2 DOT mt DOT umist DOT ac DOT uk>
Organization: Materials Science Centre
To: DJGPP AT delorie DOT com
Date: Thu, 17 Jul 1997 16:02:26 GMT-1
Subject: A funny with hooking interrupts
Reply-to: Anthony DOT Appleyard AT umist DOT ac DOT uk
Message-ID: <11F855EE6@fs2.mt.umist.ac.uk>
Precedence: bulk

  I have re-subscribed to djgpp.
  I wrote a Gnu C++ program which uses the program below to hook interrupt 9
so that it can detect all key presses and also key releases. With thanks to
Eli Zaretski for help. It works OK on my desktop. But if run on a Toshiba
Satellite laptop, the program runs OK, and duly calls clearreadkeys() before
exiting, but sometimes the laptop has errors after the program has exited:-
  (1) Sometimes on exit from the program, there is a DOS prompt, then
something about "Bad TTR" or something like that, and a hex dump, then another
DOS prompt. After that, the laptop <seems> to run OK.
  (2) Yesterday I ran the program, and exited OK; but when I then typed WIN at
the DOS prompt, Windows started as far as the initial blue screen that says
`WINDOWS' etc in big letters, then locked tight & I had to press ctrl-alt-del.
  Both these computers have DOS 6.22 & Windows for Workgroups.
  The laptop presumably has special software to translate `function' key
combinations into simulations of the full keyboard keys that aren't on the
laptop, <before> interrupt 9 looks at them. Could it be that this special
software interferes with the process of hooking and unhooking interrupt 9?

/*-----*/
volatile uns char k_after0xe0=0,Keydown[256],Keypressed[256];
_go32_dpmi_seginfo old_I9handler,new_I9handler;
/*-----*/
void I9handler() {uns char c,d; c=inportb(0x60);
if(c==0xe0) {k_after0xe0=128; return;} d=(c&127)+k_after0xe0;
if(c&128) Keydown[d]=0; else {if(!Keydown[d]) Keypressed[d]++; Keydown[d]=1;}
k_after0xe0=0;}
/*-----*/
int keypressed(uns char c){int i=Keypressed[c]; Keypressed[c]=0; return i;}
/*-----*/
void setreadkeys(){int i; for(i=0;i<256;i++) Keydown[i]=Keypressed[i]=0;
_go32_dpmi_get_protected_mode_interrupt_vector(9, &old_I9handler);
new_I9handler.pm_offset = (int)I9handler;
new_I9handler.pm_selector = _go32_my_cs();
_go32_dpmi_chain_protected_mode_interrupt_vector(9, &new_I9handler);};
/*-----*/
void clearreadkeys(){int i; for(i=0;i<256;i++) Keydown[i]=0;
_go32_dpmi_set_protected_mode_interrupt_vector(9, &old_I9handler);};
/*-----*/