IDT Link Operation
PES24T3G2 User Manual
3 - 8
February 22, 2012
Notes
PES24T3G2 on page 3-4. When the speed of the link is downgraded as a result of link retraining, the PHY
LTSSM remains at the downgraded speed until the link partner requests a link speed upgrade or software
sets the Link Retrain (LRET) bit in the PCIELCTL register.
Link Down
When a link goes down, all TLPs received by that port and queued in the switch are discarded and all
TLPs received by other ports and destined to the port whose link is down are treated as Unsupported
Requests (UR). While a downstream link is down, it is possible to perform configuration read and write
operations to the PCI-PCI bridge associated with that link. When a link comes up, flow control credits for the
configured size of the IFB queues are advertised. A link down condition on a downstream port’s link may
cause the Surprise Down Error Status (SDOENERR) bit to be set in the port’s AER Uncorrectable Error
Status (AERUES) register. The conditions under which surprise down is reported are described in Section
3.2.1 of the PCIe 2.0 Specification.
Slot Power Limit Support
The Set_Slot_Power_Limit message is used to convey a slot power limit value from a downstream
switch port or root port to the upstream port of a connected device or switch.
Upstream Port
When a Set_Slot_Power_Limit message is received by the upstream switch port, then the fields in the
message are written to the PCI Express Device Capabilities (PCIEDCAP) register of that port:
–
Byte 0 bits 7:0 of the message payload are written to the Captured Slot Power Limit Scale
(CSPLS) field.
–
Byte 1 bits 1:0 of the message payload are written to the Captured Slot Power Limit Value
(CSPLV) field.
Downstream Port
A Set_Slot_Power_Limit message is sent by downstream switch ports when either of the following
events occur:
–
A configuration write is performed to the corresponding PCIESCAP register when the link associ-
ated with the downstream port is up.
–
A link associated with the downstream port transitions from a non-operational state to an opera-
tional (i.e., up) state.
Link States
The PES24T3G2 supports the following link states
–
L0
• Fully operational link state
–
L0s
• Automatically entered low power state with shortest exit latency
–
L1
• Lower power state than L0s
• May be automatically entered or directed by software by placing the device in the D3
hot
state
–
L2/L3 Ready
• The L2/L3 state is entered after the acknowledgement of a PM_Turn_Off Message.
• There is no TLP or DLLP communications over a link in this state.
–
L3
• Link is completely unpowered and off
–
Link Down
3.
If enabled, the Autonomous Link Reliability mechanism described in section 8.7.1 may keep the link speed at
2.5 Gbps in spite of link partner requests to upgrade the link speed.
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Страница 8: ...IDT PES24T3G2 User Manual 6 February 22 2012 Notes...
Страница 12: ...IDT Table of Contents PES24T3G2 User Manual iv February 22 2012 Notes...
Страница 14: ...IDT List of Tables PES24T3G2 User Manual vi February 22 2012 Notes...
Страница 16: ...IDT List of Figures PES24T3G2 User Manual viii February 22 2012 Notes...
Страница 20: ...IDT Register List PES24T3G2 User Manual xii February 22 2012 Notes...
Страница 32: ...IDT PES24T3G2 Device Overview PES24T3G2 User Manual 1 12 February 22 2012 Notes...
Страница 72: ...IDT SMBus Interfaces PES24T3G2 User Manual 5 20 February 22 2012 Notes...
Страница 76: ...IDT Power Management PES24T3G2 User Manual 6 4 February 22 2012 Notes...
Страница 156: ...IDT Configuration Registers PES24T3G2 User Manual 8 74 February 22 2012 Notes...