🚀 go-pugleaf

 > I'm trying to write a Windows 3 application which needs to interface to a
 > DOS TSR which communicates via an interrupt. Everything works fine in real
 > mode, but I get UAEs and reboots in both standard and 386 enhanced mode.
 >
 > The code segment that's causing the trouble:
 >
 [...]
 >         hBuffer = GlobalAlloc(GHND,512L);
 >         lpBuffer = GlobalLock(hBuffer);
 >         InRegs.x.di = FP_OFF(lpBuffer);
 >         SegRegs.es = FP_SEG(lpBuffer);
 >
 >         int86x(0x7f,&InRegs,&OutRegs,&SegRegs);
 >
 > I've done a lot of RTFM-ing, but to no avail (at least, the problem
 > isn't
 > solved). I didn't write the TSR, so it's difficult to get changes done
 > there (I don't have the source).

You obviously have read the wrong manual. Ever heard of the DPMI (Dos Protected 
Mode Interface)? That should solve your problems.

The protected mode you must watch out for a lot of things you can ignore in 
real mode. Here are some of the differences:

- In protected mode the processor can access more than 1MB of memory. In real 
mode only the 1st MByte can be reached by the processor. So if you GlobalAlloc 
some memory in protected mode, that memory can be anywhere, very likely 
somewhere above 1 MB. Hence your TSR (in real mode) can _not_ reach that 
memory.
- In proteted mode all segment `addresses' are no longer `adresses'. All values 
stored in segment registers are selectors. A selector is an index in a (local 
or global) descriptor table (LDT/GDT), which contains the linear addresses for 
the segments. So a selector only identifies a segment. That si similar to the 
Windows memory handle. The segment can float in memory, but the selector 
remains valid, as long as the segment address is updated in the descriptor 
table.

- The protected mode has its own interrupt table, which is not identical with 
the real mode interrupt table. So calling a (real mode) TSR from protected mode 
must fail, because the protected mode interrupt vector does not point to the 
TSR.

Because these restrictions make it (nearly) impossible for a protected mode 
application to communicate with a real mode programm, some people from Borland, 
Microsoft, Intel, Lotus, Phar Lap etc. came together and developed the DPMI 
specification. DPMI stands for Dos Protected Mode Interface and is an API for 
protected mode programs that allows it to do several (dirty) things and tricks 
otherwise not possible in PM. A copy of that specification can freely(!) be 
orderd by Intel, Santa Clara.

This DPMI has all the functions you need to call yout TSR. Fist you must 
allocate the memory you need in the real mode addressable 1 MB region. That is 
done with function `Allocate DOS Memory Block'. The result is a selector AND 
the segment address of the memory block. Then you fill in the required register 
values for the TSR into a data area called `real mode call structur'. When 
calling the real mode program, all registers will be loaded from this 
structure. Then you can call yout TSR via the DPMI fuction `Simulate Real Mode 
Interrupt'. The TSR will (hopefully) do its job and fill the memory with the 
expected values. And don't forget to free the DOS memory block, if it is no 
longer needed.

Hope I could give you some clues...

Norbert,
Dortmund, FRG