AMD 762 Chipset Tweaking (MP/MPX) Guide

Author: Martin Krohn
Editor: Howard Ha
Publish Date: Wednesday, August 7th, 2002
Originally Published on Neoseeker (http://www.neoseeker.com)
Article Link: http://www.neoseeker.com/Articles/Hardware/Guides/amd762/
Copyright Neo Era Media, Inc. - please do not redistribute or use for commercial purposes.

In this article we are going to look at improving the performance of the AMD's 760MP/MPX chipset which is designed for multi processor use. We have been digging into the white papers on this chipset over the past week to try and find out every last thing we could about this chipset and then figure out how all of you power hungry madmen with the duallies can make it run even faster! If you've been around this site for very long you know all about chipset registers by now.

 

Please be warned that if something is set wrong it can and will cause windows to crash. Generally when you set something wrong it'll either automatically restart or you will have to press the reset button. If you do not know what one of the settings do then it is probably best that you don't change it ;)

 

A little lesson in chipset workings:

 

A LOT of the registers are nearly identical to those that are in the AMD 761 Northbridge. I did find 1 SMP related tweak that determines read ahead data but for the most part this is going to be like our AMD 761 chipset tweaking guide written by Lee. The 762 PCR file is also based on his PCR. I went over every register setting and made sure that they were the same and changed them where necessary.

 

Since a good amount of the tweaks here are memory related you should have an understanding of what they do. I wrote an article covering this kind of things and posted it here. Please keep checking it for updates because I'll continually be updating it with more DDR timings as I can.

 

What are the registers?

 

The chipset registers are pretty simple, they are memory locations in the northbridge that control the way it behaves. They control every aspect of the northbridge. Now as the northbridge is responsible for controlling the CPU, the memory bus, the AGP bus and the PCI bus, then its a pretty important part of your computer. The chipset registers are usually set by the BIOS at the time of boot-up, but by using some very useful pieces of software we can override these settings from Windows. This will help you find the maximum settings for your hardware without having to continually reboot. Of course when you set something too high your system will crash! Also some of the cheaper motherboards out there don't have all of the tweaks that are supported by the chipset. If that is the case this is the only way that you'll be able to make your system perform like you want.

 

What sort of things can be changed?

 

You can change pretty much every setting available in the BIOS plus some more that aren't. You can change all the memory settings, RAS, CAS and so on. You can change your AGP aperture size, change AGP modes from 4x to 2x or 1x...and more.

What are these programs? And where can I get them?

 

The programs we are going to look at are called WPCREDIT and WPCRSET. They are great programs written by the amazing H-Oda. Some of you are probably familiar with his work, he wrote WCPUID among other things. Now these aren’t new programs, but they are highly underused. Mainly because they can be rather hard to understand and even harder to find the proper PCR files. It's rather hard to find the documentation needed to properly write these files. AMD and Intel are both great about posting these for public download but guys like VIA, SIS and ALI all require you to know somebody on the inside to get a hold of what you need. With guys like VIA I believe this is most likely due to how small the variances between releases are.

 

The first of these programs, WCPREDIT, is used to try out new settings in Windows and see what immediate effect they have; this is great because you can try different memory settings without having to keep going to the BIOS or when your BIOS may not allow you to change these settings. Now what you have to realize is that some settings might not work, or may cause your machine to lock up. This is no problem; simply reboot and all will return to normal again.

 

The other program, WCPRSET, is used to apply the settings that you find to work when Windows starts. You will need to download the following files: wpcre12a.exe, wpcrs120.exe and AMD762.PCR

 

Before we go any further, you will need to read this article of mine HERE. That will explain alot of DDR timings to you.

Before you begin you'll need a few files:

 

·        WPCREDIT

·        WPCRSET

·        AMD 762 PCR File

 

Once downloaded you need to run both of the exe files, These will then extract all the files needed to continue. Now if you run WCPREDIT.EXE you will be presented with a screen that looks something like the following:

 

What we see in the picture above is a layout of all the registers that we will be dealing with. The registers all have locations that are determined by Hex values starting at 00 and going up to FF. If you look down the left side you will see 00-F0........... now if you wish to find say register 66 for example you would read down to 60 on the left, the go along until your in the column 06 at the top, just add the numbers together to find the location.

When you click on any given location you will see the value that is currently assigned to that register. These will be listed on the right as shown in the pic below.

 

As you will see, every register is 8 bits in size, with every bit being a different setting.

 

Now these bits don't really mean anything when you look at them like this, so we need to load the pcr file that holds the descriptions for the via chipsets.

 

To do this go to the File menu at the top of the program and you will see an option PCR Open shown below.

 

 

You will then need to load the file AMD762.PCR that should be in the directory with WPCREDIT.

 

It will give an error message saying that the Vender ID differs, just hit continue

 

Register 46

 

Speculative Read Data Movement Enable

 

In two processor systems read data commands are returned speculatively before the probe response is received. This setting changes how long after the probe is send before this action is taken. This setting uses all 8 bits in register 46 and both CPUs will need to have the same setting.

 

0000=disabled
0001=single clock
0010= 2 clocks
1111=15 clocks

 

Register 49

 

ECC

 

4 is ECC Diagnostic Mode
0 Disables ECC and 1 Enables it

 

3,2 Configure what all will be checked and corrected.
00 for this if Bit 4 is set for disabled.
01 Errors are checked for but NOT corrected
10 has some error correction but doesn't take full advantage of data integrity checking
11 This is everything that ECC can possibly offer

 

Memory Performance

 

Register 54

 

1,0 = TRCD RAS to CAS delay 11=4 cycles 10=3 cycles(default) 01=2 cycles 00=1 cycle

 

3,2 = CAS Latency 01=2 cycles 10=2.5 cycles 00=3 cycles

6,5,4 = TRAS 111=9 cycles 110=8 cycles 101=7 cycles(recomended) 100=6 cycles 011=5 cycles 010=4 cycles 001=3 cycles 000=2 cycles

This next one wants to be tricky. It spans across two different registers ;) Register 54 AND 55 both you'll have to go to for this setting.

 

54:7 + 55:0 =TRP(see bit 8) 00=3 cycles(recomended) 11=4

cycles

Register 55

 

3,2,1 TRC 111=10 cyc 110=9 cyc 101=8 cyc 100=7 cyc 011=6 cyc 010=5 cyc 001=4 cyc 000=3 cyc

 

7,6 Page Hit Limit 00=1 cycle 01=4 cycles 10=8 cycles 11=16 cycles

Register 56

2,1,0 = Idle Cycle Limit 111=disable 110=48 cyc 101=32 cyc 100=24 cyc 011=16 cyc 010=12 cyc 001=8 cycles(suggested) 000=0 cycles

Register 57

7 = Super Bypass Wait State 0=100Mhz FSB 1=133Mhz FSB
2
= Write to read Delay 0=1 cyc 1=2 cyc
1,0 = Write Recovery Time 00=1 Clock cyc 10=2 Clock cyc 11=3 Clock cyc

Register 5A

4 = Burst Refresh Enable 0=no refresh 1=Refresh Refreshes are only queued during long sequences of operation to the same memory device. When enabled the 762 will queue up to four refreshes before issuing.

1,0 = Cycles Per Refresh This is something that I simply couldn't write into the PCR file due to the variances in system buses and their resulting numbers. Please notice that 66 is half the speed as 133 and therefore the time values are exactly doubled. If you were to increase your bus speed 25% the resulting number will be 25% lower.

Register 61

1 = Super Bypass Enable 0=disabled 1=enabled

That means that all you SMP guys won't be able to see the benefits of Super Bypass

PCI Bus tweaks

Register 71

2 = PCI Pipe enable 0=disabled 1=enabled



1 = PCI Block Write Enable 0=disabled 1=enabled

Register 84

2 = AGP Prefetch Enable 0=disabled 1=enabled
This enables the system controller to prefetch data from the RAM when a PCI master on the AGP bus reads from the main memory
1 = PCI Prefetch Enable 0=disabled 1=enabled
This enables the system controller to prefetch data from the RAM when a PCI master on the PCI bus reads from the main memory

Register 88

3,2,1,0 set the CPUs multiplier Both Register 88 and 89 have settings for this.

Register 8B

0 = AMD Athlon Bus Threshold 0=1.35-1.9V 1=2.0-2.2V
I'm not finding any really helpful data on this setting but anytime something talks about a higher voltage it gets my attention. I believe this was most likely included in the chipset with future processors in mind. I have not seen any motherboards support higher than 1.9v but using this I wasn't able to do a software

AGP Status A4, A5 just tell you that the chipset supports these features.

Register A8

4 = Fast Writes Enable 0=disable 1=enable you'll have to set a register in B4 also to properly enable Fast writes

2,1,0 = AGP mode 4x,2x,1x are options. Since each one is also backwards compatible with 4x all 3 settings will be set to 1 which is enabled.

Register A9

1 = Sideband Addressing 0=disable 1=enable

Register B9

7 = Fast Writes Override 0=disabled 1=enabled fast writes will only be properly enabled if this setting and the FW setting in A8 are properly set.

6 = Force AGP 4x If you're having any problems getting 4x to work properly for you you'll want to set this to 1

WPCRSET:

Now lets have a look at the other program, WPCRSET.......

You need to install it by running the program INSTDD.EXE, this will then install the program onto your computer, you will need to reset before any changes can be made.

When you are done you will need to run WPCRSET.EXE.

You will be presented with the following screen:

This shows a register change already set for start up, the one for register 52 as you can see.

To set any registers you wish at start up you need to make sure that at the top right it is set to Start..... then simply hit Add to add a new setting to it. You will be greeted with a screen like below:

 

 

You simply enter the register number under register and the setting you wish to apply under Data, simple.

Then you'll need to restart once you are done for any changes to take place.

 

If for some reason windows doesn't like one of your settings and will not load, just hold down the Ctrl key on startup and it will bypass your startup files.

 

The End

 

Some of you will have successes with this and many of you will not. You can and very likely will lock up your system while doing this. These changes are by no means permanent. Simply restarting your system will restore anything that has been changed. Always test things with WPCREDIT before setting them in WPCRSET.

Have fun with this guide. Most of the PCR settings are the same as those in Mr Slicks 761 guide. So of course MANY thanks have gotta go out to him since his article is the basis for this one.

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