Reset and Initialization
PLX Technology, Inc.
5.1.3
Hot Reset
A Hot Reset is equivalent to a traditional Software Reset. Triggered by an in-band signal from an
upstream PCI Express link to all downstream ports, a Hot Reset causes all ports that are downstream
from the initiating port to set their registers and state machines to initial values. This type of reset does
not require power cycling, nor does it cause PEX 8532 port re-configuration. However, a Hot Reset:
• Causes all TLPs held in the PEX 8532 to be dropped
• Returns all State machines to their initial (default) values
• Returns all Non-Sticky register bits to their initial (default) conditions (refer to Table 11-3,
“Register Types, Grouped by User Accessibility,” for further details regarding Sticky register
bit types)
A Hot Reset is triggered by the following actions:
• Physical Layer (at the upstream port) receives a reset through a training sequence leading
to a Hot Reset
• Upstream PCI Express port enters the DL_Inactive state, which has the same effect as a Hot Reset
Note: In the following sections, the terms “virtual PCI-to-PCI bridge” and “port”
refer to a given Station port.
5.1.3.1
Hot Reset Propagation
Reset is propagated to a downstream PCI Express device through the PCI Express link, using the
Physical Layer Hot Reset mechanism (that is, a Reset bit in the Training Sequence Ordered-Set from the
upstream device is set).
PCI Express views a switch as a hierarchy of virtual PCI-to-PCI bridges.
An example of reset propagation across the PEX 8532 switch is illustrated in Figure 5-1. Upon
receiving a Hot Reset from the upstream PCI Express link, the virtual primary PCI-to-PCI bridge
propagates the reset to virtual secondary PCI-to-PCI bridges in the upstream and downstream ports.
Each virtual secondary PCI-to-PCI bridge propagates the reset to its downstream links, and initializes its
internal states to initial/default conditions.
A Hot Reset does not impact Clock Logic, Port Configuration, nor Sticky register bits.
Figure 5-1. PEX 8532 System Reset Propagation Example
Reset
Propagation
Upstream
Port
Upstream
P-P Bridge
P-P
Downstream
P-P Bridges
P-P
P-P
P-P
P-P
P-P
P-P
P-P
Downstream
Ports
Upstream Station
Downstream Station
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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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