Possible DDR DIMM Solution

Advanced fix for DDR problems – Klynn

ED Note: Klynn posted this in the VIA Hardware Forum and allowed us to reprint it here.

OK guys, I hope this post will eventually lead to a surefire solution to these memory problems. I personally don’t have a KR7A; however I’m planning on getting one in a couple of weeks (KR7A-133). In the meantime though, you guys could try playing with these settings to see what works. I figure the more people who look at it, the better our chances of success are.

Nearly 2 months ago, Gary posted a message containing the registers set for the KT266A chip for the Chaintec BIOS, whom he claims have registers closer to VIA’s “expected” values for the KT266A chipset. The message for reference is HERE.

Anyway, I decided to help the process along a little by spending my Easter
writing a quick PCI-editing program that attaches directly to memtest86 (v2.9). When you run it, it’ll open up a PCI Grid much like that used in WPCREDIT that you can change values in – however, this runs without an OS (this is a bootdisk).

You can type ‘t‘ to start memtest86, and pressing ESC from memtest will take you back to the PCI Editor screen – quite a nifty utility to see what works and what doesn’t.

You’ll find the program here (this is a floppy disk image, not an executable!):
pciedit.bin, and
the program you can use to write the disk image with here: rawrite.exe

My recommendation: Try setting single register values (bytes or
bits) equal to that used by the Chaintec BIOS (differences are listed below). I would recommend not touching anything unless you have a printout of the PCR file for the KT266A register set (HERE), otherwise, unless you’re very lucky, you won’t have any idea what you’re changing.

Also, I wouldn’t blindly change values with this program either because, like any of these tweaks, there is always the possibility of damaging your hardware completely, so be careful what you change.

BTW, let me know if you guys like this thing and I’ll write a quick PCI-editing floppy boot disk layer that can boot your normal OS off of the harddrive after you finish editing values.

Also, this thing couldn’t have been made without open-source software. The
source is HERE.

Thanks to Joe Citarella’s post at Overclockers.com for the initial link to your forum that got me thinking about all this.

Here’s the Register Differences listing from Gary’s last post, in the
byte-order that WPRCEDIT/PCIEDIT expects them to be in:

KR7A, 1×256 Crucial PC2100 module in DIMM1

00: 06 11 99 30 06 00 10 22 – 00 00 00 06 00 08 00 00
10: 08 00 00 e8 00 00 00 00 – 00 00 00 00 00 00 00 00
20: 00 00 00 00 00 00 00 00 – 00 00 00 00 00 00 24 08
30: 00 00 00 00 a0 00 00 00 – 00 00 00 00 00 00 00 00
40: 00 18 88 80 82 44 00 00 – 18 18 88 80 82 44 00 00
50: 17 a3 6b ea 40 84 10 10 – 60 00 08 10 10 10 10 10
60: 02 aa 00 20 e6 99 00 2e – ff 2d 86 d0 4c 0a 00 00
70: 82 c8 00 01 00 01 10 00 – 00 00 00 00 00 00 10 10
80: 0f 61 00 00 c0 00 00 00 – 02 00 00 00 00 00 00 00
90: 17 a3 6b ea 5f 1c 71 05 – 11 ff 00 00 61 11 74 00
a0: 02 c0 20 00 07 02 00 1f – 00 00 00 00 2f 02 04 99
b0: 7f 99 18 00 80 00 00 00 – 80 00 00 00 00 00 00 00
c0: 01 00 02 00 00 00 00 00 – 00 00 00 00 00 00 00 00
d0: 00 00 00 00 00 00 00 00 – 00 00 00 00 00 00 00 00
e0: 00 00 00 00 00 00 00 00 – 00 00 00 00 00 00 00 00
f0: 00 00 00 00 00 82 82 00 – 00 00 00 00 00 00 00 00

7VJDA, 1×256 SimpleTech PC2100 module in DIMM1

00: 06 11 99 30 06 00 10 22 – 00 00 00 06 00 08 00 00
10: 08 00 00 e8 00 00 00 00 – 00 00 00 00 00 00 00 00
20: 00 00 00 00 00 00 00 00 – 00 00 00 00 06 11 99 30
30: 00 00 00 00 a0 00 00 00 – 00 00 00 00 00 00 00 00
40: 00 18 88 80 82 44 00 00 – 18 18 88 80 82 44 00 00
50: 17 a3 69 ea 60 04 10 10 – 60 00 08 10 10 10 10 10
60: 02 aa 02 20 e6 99 40 20 – f3 2d 86 50 40 04 00 00
70: 82 c8 00 01 00 01 10 00 – 00 00 00 00 00 00 00 00
80: 0f 61 00 00 c0 00 00 00 – 02 00 00 00 00 00 00 00
90: 17 a3 69 ea 4f 1c 71 79 – 33 ff 00 00 21 33 74 00
a0: 02 c0 20 00 07 02 00 1f – 00 00 00 00 2f 02 04 99
b0: 7f 99 18 00 c0 00 00 00 – 80 00 00 00 00 00 00 00
c0: 01 00 02 00 00 00 00 00 – 00 00 00 00 00 00 00 00
d0: 00 00 00 00 00 00 00 00 – 00 00 00 00 00 00 00 00
e0: 00 00 00 00 00 00 00 00 – 00 00 00 00 00 00 00 00
f0: 00 00 00 00 00 82 82 00 – 00 00 00 00 00 00 00 00

Klynn