Interrupt 2Fh Function 4001h

mov ax, 4001h ; Notify Background Switch

int 2fh

Notify Background Switch notifies a VM application that it is being switched to the background. The VM application can carry out any actions, but should do so within 1000ms. This is the amount of time the system waits before switching the application.

Parameters

This function has no parameters.

Return Value

This function has no return value.

Comments

After switching to the background, the application continues to run unless it attempts to access video memory. If the video adapter is in a video mode that the virtual display device (VDD) does not support in the background, the VDD freezes the application until the application can be switched back to the foreground.

VM applications that have called Enable VM-Assisted Save/Restore (Interrupt 2Fh Function 4000h) should avoid accessing video memory and registers to avoid being frozen. Applications that have not called Enable VM-Assisted Save/Restore, call access video memory and registers since the VDD saves theses after this function returns.