Important: The information in this document is obsolete and should not be used for new development.
DoVBLTaskSlot interrupt handlers for video cards should call the
DoVBLTaskfunction to handle the execution of VBL tasks.
FUNCTION DoVBLTask (theSlot: Integer): OSErr;
- Slot number corresponding to the vertical retrace queue whose tasks are to be executed.
DoVBLTaskfunction decrements the
vblCountfield of each task in the vertical retrace queue corresponding to the
theSlotparameter (except for tasks whose
vblCountfield already contains the value 0). The function executes a task if decrementing the
vblCountfield for a task record results in a value of 0.
theSlotdesignates the slot of the primary video device, the position of the cursor is also updated.
Slot interrupt handlers for video cards need to call this function to execute any tasks in the queue for that slot. You can also call this function if you need to simulate vertical retrace interrupts.
ASSEMBLY-LANGUAGE INFORMATIONThe registers on entry and exit for
Registers on entry D0 Slot number
Registers on exit D0 Result code
To reduce overhead at interrupt time, instead of executing the
_DoVBLTasktrap, you can load the jump vector
jDoVBLTaskinto an address register and execute a
JSRinstruction using that register.
noErr 0 No error slotNumErr -360 Invalid slot number