DBI Output for AGP Trans. – BIOS Optimization Guide

DBI Output for AGP Trans. - BIOS Optimization Guide

DBI Output for AGP Trans.

Common Options : Enabled, Disabled

 

Quick Review

The full name for this BIOS feature is Dynamic Bus Inversion Output for AGP Transmitter. It is an AGP 3.0-specific BIOS feature which will only appear when you install an AGP 3.0-compliant graphics card.

When enabled, the AGP controller is allowed to use the Dynamic Bus Inversion scheme to reduce power consumption and signal noise.

When disabled, the AGP controller will not use the Dynamic Bus Inversion scheme to reduce power consumption and signal noise.

The AGP bus has 32 data lines divided into two sets. Sometimes, a large number of these data lines may switch together to the same polarity (either 1 or 0) and then switch back to the opposite polarity. This mass switching to the same polarity is called simultaneous switching outputs and it creates a lot of unwanted electrical noise at the AGP controller and GPU interfaces.

To avoid this, the AGP 3.0 specifications introduced a scheme called Dynamic Bus Inversion or DBI. It makes use of two new DBI lines – one for each 16-line set. These DBI lines are only supported by AGP 3.0-compliant graphics cards.

Dynamic Bus Inversion ensures that the data lines are limited to a maximum of 8 simultaneous switchings or transitions per 16-line set. It does so by switching the DBI line instead of the data lines when the number of simultaneous transitions exceeds 8 or 50% of the data lines. This ensures that electrical noise due to simultaneous switching outputs are minimized.

In short, DBI improves stability of the AGP interface by reducing signal noises that occur as a result of simultaneous switching outputs. It also reduces the AGP controller’s power consumption.

Therefore, it is recommended that you enable DBI Output for AGP Trans. to save power as well as reduce signal noise from simultaneous switching outputs.

 

Details

The full name for this BIOS feature is Dynamic Bus Inversion Output for AGP Transmitter. It is an AGP 3.0-specific BIOS feature which will only appear when you install an AGP 3.0-compliant graphics card.

The AGP bus has 32 data lines divided into two sets. In each set, there are 16 data lines which individually switches to either a high (1) or low (0) as it sends out data. Sometimes, a large number of these data lines may switch together to the same polarity (either 1 or 0) and then switch back to the opposite polarity.

This mass switching to the same polarity is called simultaneous switching outputs and it creates a lot of unwanted electrical noise at the AGP controller and GPU interfaces. This is only significant if the number of lines simultaneously switching to the same polarity exceeds50% of the data lines.

To avoid this, the AGP 3.0 specifications introduced a scheme called Dynamic Bus Inversion or DBI. It makes use of two new DBI lines – one for each 16-line set. These DBI lines are only supported by AGP 3.0-compliant graphics cards.

When enabled, it will ensure that the data lines are limited to a maximum of 8 simultaneous switchings or transitions per 16-line set. When the number of simultaneous transitions exceeds 8 or 50% of the data lines, the AGP controller switches the polarity of the DBI line instead. The data lines that were supposed to switch en masse to the opposite polarity remain at the same polarity.

When disabled, there will be no restrictions to the number of simultaneous switchings that the data lines can perform.

At the receiving end however, the data is reproduced exactly as it was meant to. This is because the DBI line actually serves as a reference signal for the AGP data signals! Although the data signals may have been inverted on the transmitter end, the inverted DBI signal corrects it at the receiving end.

But because only one, instead of 9 or more, data lines switched to the opposite polarity, the amount of electrical noise generated is significantly reduced. In short, DBI improves stability of the AGP interface by reducing signal noises that occur as a result of simultaneous switching outputs. It also reduces the AGP controller’s power consumption.

Therefore, it is recommended that you enable DBI Output for AGP Trans. to save power as well as reduce signal noise from simultaneous switching outputs.

 

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