First post, by alvaro84
(Foreword - I feel the need to apologize for the lack of pictures - one of the boards is built into a permanent system and it wouldn't look too useful with all the cards and cables covering most of it.)
I happen to have two, apparently identical AB-PB4 boards. For the tests I equipped both with an Am5x86-133 CPU and set the jumpers to 40MHz FSB. Both have the same jumper settings, the same BIOS settings (let alone one being often CMOS reset in the absence of a working battery), the same board revision (1.3), the same chipset revision (A1?) and even the same BIOS - and I mean I physically moved the chip from one board to the other and did testing on it too with absolutely identical BIOS.
What really confuses me is the greatly different PCI VGA performance they show. Results with a Matrox Mystique 220 PCI:
Fast board: 39321 chr/ms
Slow board: 26568 chr/ms
Fast board 103 fps
Slow board 96.8 fps
Shareware Doom demo3, 32MiB of RAM of which 8MiB was allocated for of smartdrive cache:
Fast board 1041 realtics = 71.75 fps
Slow board 1059 realtics = 70.53 fps
Vspeed, done with Asus V3000 PCI this time:
Fast board 31.33MB/s A000, 17.69MB/s LFB
Slow board 26.17MB/s A000, 17.33MB/s LFB
It seems that the issue is clearly PCI related, complex tasks like Doom aren't too deeply affected. It's also worth noting that according to vspeed LFB access seems to have some other bottleneck so the speed difference is much smaller in this area.
Motherboard settings, in both cases:
DRAM read: fastest
DRAM write: fastest
SRAM read: 2-1-1-1
SRAM write: 0WS
PCI fast back-to-back: enabled
Hidden refresh: enabled
CPU to PCI write buffer: enabled
CPU to PCI byte merge: enabled
PCI to DRAM buffer: enabled
Motherboard chip silkscreens (fast board):
Motherboard chip silkscreens (slow board):
I first had the 'fast' board and hoped to have the same stellar performance when I grabbed the second one. Now I'm completely stumped.
Does anyone have an idea what the root cause of the difference could be? Should I do a chipset register dump? If so, how?
Edit. Oh, and I even tried the FSB hotswap trick (ie. boot at 133MHz then set the jumpers to 160MHz on the fly) too that often helps to prevent other boards from halving the PCI clock at 40MHz FSB - it didn't change anything.
Shame on us, doomed from the start
May God have mercy on our dirty little hearts