Bug Report

CWSDPMI/EMM386/SCSI BIOS incompatibility

Summary:

Making a DJGPP __dpmi_int call to the disk BIOS interrupt 0x13 on machines
with SCSI drives with EMM386 loaded can cause the program to hang.  One of 
the SCSI adapters had an upgradeable BIOS, and upgrading fixed the problem. 
The other, an Adaptec 2930B, doesn't appear to be upgradeable.  EMM386
version 4.95 with CWSDPMI r5.

Analysis:

Setting a separate stack (using __dpmi_int_ss and __dpmi_int_sp) and 
recording the stack usage, the interrupt 0x13 ah=0x08 call took 194 bytes 
without EMM386 loaded, and 364 bytes with EMM386 loaded.  EMM386 hooks
interrupt 0x13.  The DPMI spec indicates interrupts should allocate and
specify their own stack if more than 60 bytes are used.  CWSDPMI only
provides 256 bytes and the stack overflowed.

Workarounds:

Provide a separate stack.  Upgrade the BIOS.  Don't use EMM386.  Increase
default CWSDPMI stack size in some future release.