Carrol Touch TouchSystems CarrollTouch Prog, Programmer'S Manual, Page: 233 / 274

Appendix D - CTKERN Function Reference CARROLL TOUCH
D-38 Touch System Programmer’s Guide
Notes
The UEH is most often used to get the touch state and to update an
internal touch state variable in the user program.
Use of reentrant function calls such as BIOS calls in the UEH is
acceptable, as is the use of CTKERN function calls. However, use of
non reentrant function calls such as DOS calls is not.
Hardware interrupts are disabled while the UEH is executing. The UEH
should execute as quickly as possible to allow the TAPI driver to
continue to process hardware interrupts from the touch system. If the
UEH takes too long to return, the TAPI driver may miss hardware
interrupts from the touch system.
The UEH is called once and only once each time the touch state
changes.
While the UEH is disabled, CTKERN continues to update the touch
state. When re-enabled after being disabled, the UEH is NOT called to
notify you of any change in the touch state that may have occurred
during the time that the UEH was disabled.
Before terminating the user program, be sure to disable the UEH.
Otherwise, when the CTKERN driver calls the address of where the
application program’s event handler was, it will now be an invalid
address.