Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.csd.uwm.edu!cs.utexas.edu!uunet!ncrlnk!ncr-sd!hp-sdd!hplabs!hpfcso!hpldola!hpctdlb!hpctdls!wei From: wei@hpctdls.HP.COM (Bill Ives) Newsgroups: comp.sys.ibm.pc Subject: Re: Can I call a TSR from protected mode? Message-ID: <2010015@hpctdls.HP.COM> Date: 6 Sep 89 14:20:10 GMT References: Organization: Hewlett-Packard CTD, Colo. Spgs. Lines: 37 >/ hpctdls:comp.sys.ibm.pc / kevin@harpo.doc.ic.ac.uk (Kevin Twidle) / 11:07 am Sep 5, 1989 / >I have a TSR that I want to be able to call from a protected mode >program running under DOS. This really boils down to causing an >interrupt in protected mode. > >I know nothing about protected mode :-( It this possible? easy? hard? >Can anyone give me some names of any good books on the subject? >Thanks in advance >Kevin (kpt@doc.ic.ac.uk) What it really bois down to is how ( or through what program ) you got into protected mode from where you wish to run your TSR. Using protected mode ISR ( interrupt service routines ) is no easy affair since the vector table ( called the IDT - Interrupt Descriptor Table ) can be located anywhere and may be almost any size. I suggest you read INTEL'S 80386 Programmer's Reference Manual if you want the gory details. Some protected mode programs ( like Smalltalk V/286 ) are curtious enough to "mirror" the real mode vector table into their IDT so that TSR will be invoked AFTER switching back to real mode from protected mode. Other programs or operating systems are not as easy... it is practically impossible ( I would say impossible ) to have a TSR in OS/2 since it uses the protected mode previledge level features. As far as other good books.. I have found very little about pure protected mode programming -- some books give cursory glances at switching modes ( read <-> protected ) -- but other than that I have had to learn everything else on my own through expermentation ( remember there is no protected mode debugger available other than under OS/2 where you can't do any real protected mode programming anyway.) Drop me a line if you have any specific questions concerning protected mode programming... its not for the light of heart. Bill Ives HP CTD #include