Chapter 5 Reset and Initialization
5.1
Reset Overview
Reset is a mechanism that returns a device to its initial state. Hardware or software mechanisms can
trigger a reset. The re-initialized states following a reset vary, depending on the reset type and condition.
The PCI Express Base r1.0a, Section 6.6, defines the hardware mechanism as Fundamental Reset.
Two actions can trigger a Fundamental Reset:
• Cold Reset
• Warm Reset
There is also a type of reset triggered by an in-band signal from an upstream PCI Express link to all its
downstream ports, which is called a Hot Reset.
There is also a Secondary Bus Reset. Any PCI-to-PCI bridge can reset its downstream hierarchy by
setting the Bridge Control register (BCR) Secondary Bus Reset bit (offset 3Ch[22]=1).
Upon exit from a Cold or Warm Reset, all port configurations, port registers, and state machines are set
to initial (start-up) values, as specified in Section 5.2, “Initialization Procedure.”
5.1.1
5.1.2
Cold Reset
A Cold Reset is a Fundamental Reset that occurs following a proper PEX 8532 power-on. When the
PEX_PERST# signal is held Low following the proper application of power to the device,
a Fundamental Reset occurs.
A Fundamental Reset initializes the entire PEX 8532 device (such as configuration information, clocks,
state machines, registers, and so forth).
When power is removed from the device, or travels outside the required ranges, all settings and
configuration information is lost. The device must cycle through the entire Initialization Procedure after
power is accurately re-applied.
Warm Reset
The Fundamental Reset mechanism can also be triggered by driving the PEX 8532 hardware Reset
signal (PEX_PERST#) Low, without the removal and re-application (recycling) of power. This is
considered a Warm Reset.
PEX_PERST# can be controlled by on-board toggle switches or other external hardware resets to the
device. The device must cycle through the entire Initialization Procedure after the PEX_PERST# input
signal is returned to High.
ExpressLane PEX 8532AA/BA/BB/BC 8-Port/32-Lane Versatile PCI Express Switch Data Book
Copyright © 2007 by PLX Technology, Inc. All Rights Reserved – Version 1.6
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