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Datasheet, Volume 2

227

Processor Configuration Registers 

31

RW

0b

Uncore

Virtual Channel enable (VCMEN) 
0 = Virtual Channel is disabled. 
1 = Virtual Channel is enabled. See exceptions below. 
Software must use the VC Negotiation Pending bit to check 

whether the VC negotiation is complete. When VC Negotiation 

Pending bit is cleared, a 1 read from this VC Enable bit indicates 

that the VC is enabled (Flow Control Initialization is completed for 

the PCI Express port). A 0 read from this bit indicates that the 

Virtual Channel is currently disabled. 
BIOS Requirement: 

1.

To enable a Virtual Channel, the VC Enable bits for that 

Virtual Channel must be set in both Components on a Link. 

2.

To disable a Virtual Channel, the VC Enable bits for that 

Virtual Channel must be cleared in both Components on a 

Link. 

3.

Software must ensure that no traffic is using a Virtual 

Channel at the time it is disabled. 

4.

Software must fully disable a Virtual Channel in both 

Components on a Link before re-enabling the Virtual 

Channel.

30:27

RO

0h

26:24

RW

111b

Uncore

Virtual Channel ID (VCID) 
This field assigns a VC ID to the VC resource. Assigned value 

must be non-zero. This field cannot be modified when the VC is 

already enabled. 

23:8

RO

0h

7:0

RO

80h

Uncore

Traffic Class/Virtual Channel Map (TCVCMMAP): 
This field indicates the TCs (Traffic Classes) that are mapped to 

the VC resource. Bit locations within this field correspond to TC 

values. 
For example, when bit 7 is set in this field, TC7 is mapped to this 

VC resource. When more than one bit in this field is set, it 

indicates that multiple TCs are mapped to the VC resource. In 

order to remove one or more TCs from the TC/VC Map of an 

enabled VC, software must ensure that no new or outstanding 

transactions with the TC labels are targeted at the given Link.