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ASUS V9280
A Case Study of AGP 3.0
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| (Review by MS, Dec. 9, 2002) |
Mode Confirmation
We elaborated earlier on the reciprocal signalling scheme between mainboard and graphics card to enable AGP 3.0 features and that AGP 3.0 is not necessarily synonymous with AGP 8X transfer mode. Since the ASUS A7N8X has the option of disabling AGP 8X in the BIOS we were curious whether this means a simple scaling back from ODR to QDR as provided for by the AGP 3.0 specifications or whether the BIOS switch would simply pull pins A3 and A11 up to make them look like no connects (NC) and, by this means, force the system to run in AGP 2.0 mode.
Fortunately, the latest version of Hiroshi Oda's WCPUID also queries the AGP protocol version alomg with the actual transfer mode. Let's take a look at what WCPUID tells us about the different modes.
AGP 8X Enabled in BIOS
Somehow it is not surprising that WCPUID does not correctly identify the chipset and / or AGP data rate. It is a new chipset and there will be updated versions shortly. Note the different columns for Status (data) and Command settings with the latter being exclusively confined to the SBA path in AGP 3.0. Note the contradiction in the SBA fields regarding SBA stating that it is not supported but enabled. Bottom line is that the chipset information generates some wrong entries and we are not trying to point fingers here but simply to avoid confusion.
AGP 8X Disabled in BIOS
Disabling the AGP 8X transfer rate in the BIOS still shows the AGP3.0 transfer protocol in place. Considering the novelty of the chipset, we tentatively overlook the fact that the data rate is now listed as 8x instead of 4x (we will keep it in the back of our mind, though). Theoretically, SBA should run in the same mode as the data transfer, that is 8X in AGP 8X and 4X in AGP 4X but there may be exceptions we don't know about.
The burning question now was what was going to happen if we taped over pins A3 and A11, that is , if we could force the AGP 2.0 protocol on the same card and, thus, get a handle on what is transfer rate and what is sideband addressing and related improvements.
AGP 8X Disabled in BIOS
After taping over the pins responsible for enabling AGP 3.0 mode we get the above picture. The protocol changes to AGP 2.0 which is supported by the hardware, the possible modes, that is 1X, 2X and 4X are listed. Also, SBA is listed as both supported and enabled.
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