L O S T C I R C U I T S

BIOS

As with all their current boards, ASUS is using the Award Medallion BIOS. There are no particular issues with this BIOS, basically all settings are documented in the LostCircuits BIOS Guide. A few points are worth mentioning, though.

If running a 133/266 MHz FSB CPU, the DRAM frequency cannot be increased by 33%. This is perfectly normal since, in this case, the DRAM already runs in PC133 mode. Kind of surprising, though, was the finding that the memory bus cannot be run at -PCI speed, leaving PC133 Mode as the only possible option at 133 MHz and above. In terms of performance this makes perfectly sense since a 133 MHz FSB would choke on a 100 MHz SDRAM bus.

The CPU frequency can be increased in 1 MHz steps up to 154 MHz. Above that, the speed will default back to 150 MHz when the setting is saved to the CMOS. This redirect matches quite well the performance / stability characteristics of the chipset. In order to access these settings, the board needs to be set to jumperfree mode with the concurrent loss of manual setting of the multiplier value. Below 100 MHz, 90 and 95 MHz settings are available.

The A7V133 can be set in the BIOS to run at Optimal or Normal system performance. Optimal performance enables Bank Interleaving, Burst Refresh (to reduce the penalty of intermittent refreshes) and 4k page size. As pointed out on VR-Zone, the System Performance Setting toggles between optimal and normal, that is, above 138 MHz, the normal setting kicks in automatically, if the bus speed is lowered, it defaults back to the optimal setting.

Screenshot of WPCredit showing the bit assignments of the different chipset registers at 137 MHz, optimal setting. The cursor is over "offset 66" which defines the state-machine for DIMM slot #1 and shows a Hex value of 52. The binary code ending in 10 shows that 4 way interleaving is enabled. When increasing the bus speed to 138 MHz, the BIOS changes to "normal performance" which flips offset 66, 69 and 7A to turn off 4 way interleaving, 4K page boundary and burst refresh mode, all of which are sensitive to timing. The main parameter for performance, though, is bank interleaving, changing any of the other parameters manually went unnoticed by benchmarks but caused immediate system crash at higher bus speed.

Register setting at 138-148 MHz as comparison to the 133-137 MHz settings above

ASUS has still kept some of the ISA legacy options like Delayed Transaction in the BIOS. At this point there are no ISA slots included on the A7V133, however since spin-offs of the diverse ASUS boards are the main business in the OEM channel, there is always a possibility that a customer requests such feature and, consequently, complete removal of the option could only create additional problems.

IRQ Assignement

Like all current ASUS boards, the A7V allows to manually assign specific IRQs to individual PCI slots. IRQ management is done in hardware, courtesy of the on-board ASUS ASIC, which, however, requires PnP OS installed set to enabled.

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