PEG Port VC1/Map – The Tech ARP BIOS Guide

PEG Port VC1/Map - The Tech ARP BIOS Guide

PEG Port VC1/Map

Common Options : Disabled, TC1, TC2, TC3, TC4, TC5, TC6, TC7

 

Quick Review of PEG Port VC1/Map

Unlike the sideband signals used to prioritize traffic on the AGP or PCI bus, PCI Express uses virtual channels and traffic classes (also called transaction classes) to decide what traffic gets a higher priority to bandwidth on the bus at any particular time.

The PEG Port VC1/Map BIOS feature allows you to manually map a specific traffic class to the second (VC1) virtual channel of the PCI Express graphics port. This is the higher-priority virtual channel, so mapping a specific traffic class to it will increase bandwidth allocation priority for that traffic class. However, this is not a requirement.

When set to Disabled, no traffic class will be manually mapped to the VC1 virtual channel.

When set to TC1, the TC1 traffic class will be manually mapped to the VC1 virtual channel. This allows traffic with a higher priority than TC0 to be given access to a higher priority virtual channel.

When set to TC2, the TC2 traffic class will be manually mapped to the VC1 virtual channel. This allows traffic with a higher priority than TC1 to be given access to a higher priority virtual channel.

When set to TC3, the TC3 traffic class will be manually mapped to the VC1 virtual channel. This allows traffic with a higher priority than TC2 to be given access to a higher priority virtual channel.

When set to TC4, the TC4 traffic class will be manually mapped to the VC1 virtual channel. This allows traffic with a higher priority than TC3 to be given access to a higher priority virtual channel.

When set to TC5, the TC5 traffic class will be manually mapped to the VC1 virtual channel. This allows traffic with a higher priority than TC4 to be given access to a higher priority virtual channel.

When set to TC6, the TC6 traffic class will be manually mapped to the VC1 virtual channel. This allows traffic with a higher priority than TC5 to be given access to a higher priority virtual channel.

When set to TC7, the TC7 traffic class will be manually mapped to the VC1 virtual channel. This allows only traffic with the highest priority to be given access to a higher priority virtual channel.

Generally, it is recommended that you leave this BIOS feature at the default setting of TC7. This allows only the highest priority traffic to be given access to the higher priority VC1 channel.

 

Details of PEG Port VC1/Map

Unlike the sideband signals used to prioritize traffic on the AGP or PCI bus, PCI Express uses virtual channels and traffic classes (also called transaction classes) to decide what traffic gets a higher priority to bandwidth on the bus at any particular time.

PCI Express requires each port to support at least one, and up to eight Virtual Channels (VC0 to VC7). Each port is also required to support at least one, and up to eight Traffic Classes (TC0 to TC7). In short, each port must support at least VC0 and TC0. It can support additional virtual channels or traffic classes up to VC7 and TC7, but that is optional.

Virtual channels are used to allow easy division of bandwidth according to demand and availability. Each virtual channel has its own set of queues, buffers and control logic, which allow independent flow control between multiple virtual channels.

If more than one virtual channel is supported, each subsequent virtual channel has a higher priority than the default VC0 channel. In other words, VC1 has a higher priority than VC0, but a lower priority than VC3. The last virtual channel, VC7, has the highest priority.

Traffic classes, on the other hand, are used to separate system traffic into different priority levels. If more than one traffic class is supported, each subsequent traffic class is higher in priority than the default TC0 class. In other words, TC1 traffic is higher in priority than TC0, but lower in priority than TC3. The last traffic class, TC7, is the highest in priority.

The PCI Express specifications require TC0 to be mapped to VC0 at the very least. This is essentially hardwired. The other virtual channels and traffic classes can be assigned to each other as required. There are just some considerations to note :

  • A single virtual channel can be shared by multiple traffic classes (i.e. VC0 can be shared by TC0, TC1 and TC2)
  • Each traffic class must be assigned to a virtual channel. There can be no unassigned traffic class.
  • Each traffic class can be assigned to only one virtual channel. It cannot be shared by multiple virtual channels. (i.e. TC1 cannot be assigned to both VC0 and VC1)

The PEG Port VC1/Map BIOS feature allows you to manually map a specific traffic class to the second (VC1) virtual channel of the PCI Express graphics port. This is the higher-priority virtual channel, so mapping a specific traffic class to it will increase bandwidth allocation priority for that traffic class. However, this is not a requirement.

When set to Disabled, no traffic class will be manually mapped to the VC1 virtual channel.

When set to TC1, the TC1 traffic class will be manually mapped to the VC1 virtual channel. This allows traffic with a higher priority than TC0 to be given access to a higher priority virtual channel.

When set to TC2, the TC2 traffic class will be manually mapped to the VC1 virtual channel. This allows traffic with a higher priority than TC1 to be given access to a higher priority virtual channel.

When set to TC3, the TC3 traffic class will be manually mapped to the VC1 virtual channel. This allows traffic with a higher priority than TC2 to be given access to a higher priority virtual channel.

When set to TC4, the TC4 traffic class will be manually mapped to the VC1 virtual channel. This allows traffic with a higher priority than TC3 to be given access to a higher priority virtual channel.

When set to TC5, the TC5 traffic class will be manually mapped to the VC1 virtual channel. This allows traffic with a higher priority than TC4 to be given access to a higher priority virtual channel.

When set to TC6, the TC6 traffic class will be manually mapped to the VC1 virtual channel. This allows traffic with a higher priority than TC5 to be given access to a higher priority virtual channel.

When set to TC7, the TC7 traffic class will be manually mapped to the VC1 virtual channel. This allows only traffic with the highest priority to be given access to a higher priority virtual channel.

Generally, it is recommended that you leave this BIOS feature at the default setting of TC7. This allows only the highest priority traffic to be given access to the higher priority VC1 channel.

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