Subj : Interrupts
To   : Vitus Jensen
From : Murray Lesser
Date : Fri May 25 2001 10:13 am

(Vitus Jensen wrote to Lee Aroner on 05-24-01:

Hi Vitus--

VJ>I would like to have an Intel or AMD manual about the i386
 >because this stuff IMHO is best explained by the processor
 >vendor but I have only a bad german short reference.  One
 >of these days I should "lend" one from the library...

   I have an old (vintage 1987) book by Stephen P. Morse, Eric J.
Isaacson, and Douglas J. Alpert:  "The 80386/387 Architecture" [ISBN
0-471-85352-0012].  Morse was the architect of the 80386.  I imagine
that this book is now out of print.  You might be able to find it in a
secondhand bookstore, or on some Web bookstore site (avoid amazon.com
except as a last resort; they charge entirely too much for out-of-print
books.  bibliofind.com now belongs to amazon.com, so they, too, are
useless.  Try ABEbooks.com.  There may be others.)

   There is a description of call gates and the rationale for using
them to access operating-system functions given in this book, but the
material is too long for me to copy here.

   As I am sure that you know (but perhaps Lee does not):  The DOS
interrupt system is emulated, not executed, when operating in a VDM.
When running in a VDM, OS/2 2.0 and later use "Virtual Device Drivers"
to emulate DOS API calls.  For calls to allowable device drivers, the
VDD calls on the appropriate OS/2 real device driver.  Some DOS programs
"hook" hardware interrupts; OS/2 virtual device support allows a few DOS
hardware interrupts to be "hooked" in VDM sessions under restricted
conditions.  For software interrupts, most allowable calls are executed
by the appropriate VDD.  The supported INT 15h (System Services) calls
are routed directly to the appropriate ROM BIOS routines by the "Virtual
ROM BIOS Driver."  In general, "allowable" DOS emulation is limited to
those DOS API calls that will not compromise the integrity of the
underlying OS/2 operating system.  See the IBM OS/2.0 Technical Library
manual "Virtual Device Driver Reference" for further information.

Regards,

       --Murray
<Team PL/I>

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