Across the Boards
Communications Device Drivers
Section 5 - General Configuration and Usage Information
Page 197
cfSOFTWARE Confidential,
2000
5.12 DOS HLLAPI Passthroughs
Numerous Windows, Windows NT/95 and OS/2 3270 emulators provide virtual device drivers which provide
DOS applications access to the Windows emulator’s HLLAPI via the traditional DOS HLLAPI (Interrupt 7F)
interface (using CFXHLLX.BIN, driver #14).
While we strive to support these interfaces, there have been many problems, and performance is generally poor
(often very poor). Accordingly we recommend that a Windows based application, using
Across the Boards
for
Windows, be used rather than a DOS application.
If a DOS passthough HLLAPI must be used, insure the following:
- Ensure that only one 3270 emulator has been installed on the machine in question (including
different releases of the same emulator). The presence of two HLLAPI interfaces, and two virtual
device drivers almost invariably leads to problems (ranging from inconsistent results to total
failure to connect).
- Ensure that the Windows emulator is up and running before the DOS
session
in which the DOS
application is to be run is started. Many problems have been encountered initializing the DOS
HLLAPI interface when this is not done.
- Do not depend on any “autostart” facilities in the emulator -- again, insure that the emulator is up
and running before running the DOS application.
- Ensure that the DOS session is not set to exclusive execution and is enabled for background
execution.
- If problems occur, try running the DOS session both windowed and full-screen.
- If performance is poor, try adjusting the DOS session execution priorites to very low or very high
values.
- Be sure to restart Windows after installing an emulator or making any configuration changes to the
emulator before trying to use a DOS HLLAPI passthrough.
- If a configuration works, try to avoid changing it or applying patches or upgrades to the 3270
emulator. DOS HLLAPI passthrough stability has often varied from release to release and from
patch to patch. Also, installing an upgrade may lead to the “multiple HLLAPI installed” problem
described above. If it is necessary to perform an upgrade, strongly consider uninstalling the old
release first, then manually deleting any files from the old emulator that may still exist, and then
manually editing the SYSTEM.INI and WIN.INI (or the registry under NT/95, or CONFIG.SYS
under OS/2) and removing any remaining references to the old emulator before restarting the
operating system and installing the new release.
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