TABLE OF CONTENTS The concept of surprise removal is often equated to hot swapping. For the most part this is accurate since a hot swap is the removal of a device without any software interaction. Unfortunately the concept of no software interaction is pretty broad. In the context of this section, PCI Express buffer architecture and detect mechanisms are addressed.
PCI Express physical architecture is designed with ease of use in mind. To support this concept PCI Express has built in the ability to handle surprise insertion and removal of PCI Express devices. All transmitters and receivers must support surprise insertion/removal without damage to the device. The transmitter and receiver must also be capable of withstanding sustained short circuit to ground of the differential inputs/outputs TX/RX+ and TX/RX .
A PCI Express device can assume the form of an add-in card, module, or a soldered-down device on a PC platform. In the case of an add-in card or module, PCI Express allows a user to insert or remove a device (an upstream port) while the system is powered.
A link that is missing a downstream device causes the upstream device to remain in the detect state. Every 12 milliseconds the downstream port checks the link to see whether or not downstream device has been connected. As soon as a user inserts a device into the system it is detected and the link training process as previously described begins.
If a downstream device is removed from the system during...
