PCI Express Base Specification v1.0 - 2002.pdf

PCI EXPRESS BASE SPECIFICATION, REV. 1.07.7.1.2.3. MRL SensorThe MRL Sensor is a Switch, optical device, or other type of sensor that reports the positionof a slot’s MRL to the port. The MRL Sensor reports closed when the MRL is fully closedand open at all other times (that is, fully open and intermediate positions).If Vaux is wired to hot-plug slots, the signals switched by the MRL must be automaticallyremoved from the slot when the MRL Sensor indicates that the MRL is open and must berestored to the slot when the MRL Sensor indicates that MRL has closed again.The MRL Sensor allows the port to monitor the position of the MRL and therefore allowsthe port to detect unexpected openings of the MRL. When an unexpected opening of theMRL associated with a slot is detected, the port changes the state of that slot to disabled andnotifies system software. The port does not autonomously change the state of either thePower Indicator or Attention Indicator.7.7.1.2.4. Electromechanical InterlockAn electromechanical interlock is a mechanism for physically locking the add-in card orMRL in place until the system software and port release it. Implementation of the interlockis optional. There is no mechanism in the programming interface for explicit control ofelectromechanical interlocks. The Standard Usage Model assumes that if electromechanicalinterlocks are implemented, they are controlled by the same port output signal that enablesmain power to the slot. Systems may optionally expand control of interlocks to providephysical security of the add-in cards.7.7.1.2.5. Attention ButtonAn Attention Button is a momentary-contact push-button, located adjacent to each hot-plugslot or on a module that is pressed by the user to initiate a hot-insertion or a hot-removal atthat slot.The Power Indicator provides visual feedback to the human operator (if the system softwareaccepts the request initiated by the Attention Button) by blinking. Once the Power Indicatorbegins blinking, a 5-second abort interval exists during which a second depression of theAttention Button cancels the operation.If an operation initiated by an Attention Button fails for any reason, it is recommended thatsystem software present a message explaining the failure via a software user interface or addthe message to a system log.7.7.1.2.6. Software User InterfaceSystem software provides a user interface that allows hot-insertions and hot-removals to beinitiated and that allows occupied slots to be monitored. A detailed discussion of hot-pluguser interfaces is operating system specific and is therefore beyond the scope of thisdocument.On systems with multiple hot-plug slots, the system software must allow the user to initiateoperations at each slot independent of the states of all other slots. Therefore, the user is370