🚀 go-pugleaf

In article <4012@news.duke.edu> jan@acpub.duke.edu (Jan Gittelman) writes:
>Hi,
>
>Has anyone managed to use IOPL to access hardware ports? I'm having trouble 
>with it. I get an access violation (SYS3175) whenever the code tries to call 
>a subroutine in the IOPL'd (ring 2) segment.
>
>I'm currently using a 16 bit compiler (Microsoft 6.00A) and assembler 
>(Microsoft 5.1). There are 6 assembler subroutines that do the actual 
>i/o and the rest of the code is written in C. I have a .DEF file to define the
>assembler routines segment as IOPL and list the exported subroutines. In fact,
>it follows the examples in both Duncan's "Advanced OS/2 Programming" and 
>Steven Mastrianni's "Writing OS2 2.0 Device Drivers in C".

I have used IOPL code in my SCRUTIL screen saver. This is a 16-bit
program, and I have not yet tried such things in a 32-bit app. You need
to follow the following steps:

- isolate the code with I/O instructions in one segment (use MS C -NT
  option to give this module a special name instead of _TEXT)
- mark this segment name as IOPL in the module definition file
- use the DosPortAccess call before doing actual port I/O
- set IOPL=YES in config.sys or add the module name to the IOPL list

This is what I did in SCRUTIL and it works under 1.x and 2.0.

Kai Uwe Rommel

/* Kai Uwe Rommel --- rommel@informatik.tu-muenchen.de */

DOS ... is still a real mode only non-reentrant interrupt
handler, and always will be.                -Russell Williams