Under Win32 (9x/NT/XP/2000/2003/Vista), the design of event (usually caused by interrupt) sets an event flag on, every time the interrupt occurs, and invokes the event service routine, which is triggered by a particular event. With this event scheme, while system loading is heavy, it often happens that several consecutive interrupts, which set the same event flag on, will be just handled once.
Due to the uncertainty of such an event scheme, functions like sio_break_irq(), sio_cnt_irq(), sio_Tx_empty_irq() and sio_modem_irq() (or named sio_xxx_irq() functions in short) may not respond the exact times of interrupt occurrence.
In addition, within sio_xxx_irq() event service routine, there have no reentrance problem and thus no prohibition of functions like printf().
Only '1' is available for the count parameter of sio_cnt_irq().
For VB, the functions, sio_xxx_irq() are not supported.