User`s guide

I/O Register Access from S-Functions Limitation
B-3
Incompatibility with Win32 API Calls
The Real-Time Windows Target kernel intercepts the interrupt from the
system clock. It then reprograms the system clock to operate at a higher
frequency for running your real-time application. At the original clock
frequency, it sends an interrupt to the Windows operating system to allow
Windows applications or any software using the Win32 API to run.
As a result, software that uses the Win32 API cannot be executed as a
component of your real-time application. Any software you use to write I/O
drivers must not have any calls to the Win32 API.