richard@calvin.spp.cornell.edu (Richard Brittain) (04/14/90)
A while ago I requested help on a problem with writing my own critical error
handler in Turbo C. Well, I finally cracked this one, so in case anyone is
interested: DONT USE BIOSKEY() in this or any other interrupt handler.
It would seem logical that bioskey() might be safe, and indeed someone posted
code here not long ago with bioskey in and int24 handler. Well with TC 2.0
and DOS 4.01 at least, the combination does not work. I wrote my own bioskey
(it's only a 10 line function anyway) and everything works fine.
Richard Brittain, School of Elect. Eng., Upson Hall
Cornell University, Ithaca, NY 14853
ARPA: richard@calvin.spp.cornell.edu
UUCP: {uunet,uw-beaver,rochester,cmcl2}!cornell!calvin!richardralf@b.gp.cs.cmu.edu (Ralf Brown) (04/14/90)
In article <1990Apr14.031218.13912@calvin.spp.cornell.edu> richard@calvin.spp.cornell.edu.UUCP (Richard Brittain) writes: }A while ago I requested help on a problem with writing my own critical error }handler in Turbo C. Well, I finally cracked this one, so in case anyone is }interested: DONT USE BIOSKEY() in this or any other interrupt handler. } }It would seem logical that bioskey() might be safe, and indeed someone posted }code here not long ago with bioskey in and int24 handler. Well with TC 2.0 }and DOS 4.01 at least, the combination does not work. I wrote my own bioskey }(it's only a 10 line function anyway) and everything works fine. That's because the TC 2.0 bioskey() grabs INT 1Bh (the Control-Break interrupt) before calling the INT 16h service and then restores it afterwards. It does this by calling INT 21h, which is off-limits in an interrupt handler. On the other hand, if it didn't do something about INT 1Bh, pressing ^Break would interrupt the program on the next DOS call which checks for ^C/^Break *in*addition*to* returning the 0000h from the INT 16h call. -- {backbone}!cs.cmu.edu!ralf ARPA: RALF@CS.CMU.EDU FIDO: Ralf Brown 1:129/46 BITnet: RALF%CS.CMU.EDU@CMUCCVMA AT&Tnet: (412)268-3053 (school) FAX: ask DISCLAIMER? | _How_to_Prove_It_ by Dana Angluin 20. by vehement assertion: It What's that?|is useful to have some kind of authority relation to the audience