Method, apparatus, and system of detecting a hot-plug event. The hot-plug event detection may be done in-band or out-of-band. The in-band detection is performed by a state machine and the out-of-band detection is performed by a logic. A circuitry is to detect a hot-plug event when inserting or removing a device from an extension bus of the plurality of extension bus slots. The circuit is to generate a hot-plug message to notify the hot-plug event. The circuitry including the state machine, the logic and a register to provide at least two bits to mask at least two states of the state machine.