AMD 785G/SB750 voltages, undervolting and overclocking (MSI)

[quest_for_silence]

Hi all!

I'd like to tweak the BIOS in a MSI 785GM-E65 board, but its Cell menu lacks of any indication about standard/default values (apart of the meaningless AUTO setting, which I won't rely upon as it's often proven wrong for things such as RAM). Or so it seems to me.

After a quick search over the web I have been unable to find out a convenient, comprehensive source for these data.

So I ask to you: which are the reference values for this chipset?
I mean those:

CPU VDD Voltage
CPU-NB VDD Voltage
CPU-NB Voltage
NB Voltage
HT Link Voltage
SB Voltage

Which are the lowest (lower than reference ones) safe values to undervolt the entire mobo (not only the CPU)?

Which are the lowest (but higher than reference ones) safe values to overclock the system?

Summarizing, which are the safe (POST + boot the O.S.) operation ranges for these voltages?

Any hint is welcome.

Regards,
Luca

[frostedflakes]

First thing I would do is hook up a Kill-A-Watt or something similar, try tweaking the voltages, and see if any have a measurable effect on power consumption or temps in Windows. My old Gigabyte 785G board didn't have nearly as many voltage tweaking options as the 785GM-E65, but I think I messed around a bit with CPU-NB undervolting and it didn't really have any significant effect on temps or power consumption. So it didn't really seem worth the time to find the lowest stable voltage for this parameter. I'd assume that would be the case for most of the voltages you have available in the BIOS.

[andymcca]

I will try to remember to post the default voltages from my ASUS board when I get home. I think the BIOS says the defaults, but I looked up the manual and it does not have them :(

Ditto what frostedflakes says, though. I had a minimalist 785g setup, and I found it idled at around 50W (AC) with default voltages, and I could only drop it to 40W with slightly unstable undervolt/underclock settings. I never settled on a stable setup because I decided the 20% reduction was not worth it. I can say I was shocked how low the chipset voltage could go and still boot.

I'll post more when I get home (unless I totally forget, which is like me).

PS this was with a single flash drive, no networking, and a Sempron 140... So almost all that power was the Mobo :(

[quest_for_silence]

While waiting for my sort of kill-a-watt (and andymcca), I've explored the area of permissible operation, finding some stable points.

So, given these stock settings:

Code: Select all

FSB 200MHz (2.300 GHz) 
CPU-NB Ratio Auto (x10) 
FSB/DRAM Ratio Auto (1:3.33) 
HT Link Speed 2000MHz (x10) 
 
CPU VDD Auto 
CPU-NB VDD Auto 
CPU Voltage Auto (1.056V reported in BIOS and CPU-Z) 
CPU-NB Voltage Auto 
DRAM Voltage Auto (1.584V reported in AMD OverDrive) 
NB Voltage Auto 
HT Link Voltage Auto 
SB Voltage Auto 

I can increase FSB up to 235MHz with these settings:

Code: Select all

FSB 235MHz (2.702GHz) 
CPU-NB Ratio x9 
FSB/DRAM Ratio 1:3.33 
HT Link Speed 2115MHz (x9) 
 
CPU VDD 1.100V 
CPU-NB VDD 1.100V 
CPU Voltage 1.107V (1.072V reported in BIOS and CPU-Z) 
CPU-NB Voltage 1.108V 
DRAM Voltage Auto (1.584V reported in AMD OverDrive) 
NB Voltage 1.108V 
HT Link Voltage 1.202V 
SB Voltage Auto 

Then to increase furtherly the FSB I have to raise again some voltages: for up to 250MHz

Code: Select all

FSB 250MHz (2.875GHz) 
CPU-NB Ratio x8 
FSB/DRAM Ratio 1:2.66 
HT Link Speed 2000MHz (x8) 
 
CPU VDD 1.100V 
CPU-NB VDD 1.100V 
CPU Voltage 1.170V (1.136V reported in BIOS and CPU-Z) 
CPU-NB Voltage 1.189V
DRAM Voltage Auto (1.584V reported in AMD OverDrive) 
NB Voltage 1.1223V 
HT Link Voltage 1.326V 
SB Voltage Auto 

while up to 261MHz (I guess I've reach the thermal limits of my systems, as CPU and system temps doesn't stabilize while running Prime95)

Code: Select all

FSB 261MHz (3.001 GHz) 
CPU-NB Ratio x8 
FSB/DRAM Ratio 1:2.66 
HT Link Speed 2088MHz (x8)
 
CPU VDD 1.100V 
CPU-NB VDD 1.100V 
CPU Voltage 1.250V (1.224V reported in BIOS and CPU-Z) 
CPU-NB Voltage 1.279V 
DRAM Voltage Auto (1.584V reported in AMD OverDrive) 
NB Voltage 1.1292V 
HT Link Voltage 1.402V 
SB Voltage Auto 

Then I've tried the undervolting.
At near the stock speed the system boots O.S. fine as low as:

Code: Select all

FSB 200MHz (2.000 GHz - FSB multiplier x10) 
CPU-NB Ratio Auto (x10) 
FSB/DRAM Ratio Auto (1:3.33) 
HT Link Speed 2000MHz (x10) 
 
CPU VDD Auto 
CPU-NB VDD Auto 
CPU Voltage 0.995V (0.952V reported in BIOS and CPU-Z) 
CPU-NB Voltage Auto 
DRAM Voltage Auto (1.584V reported in AMD OverDrive) 
NB Voltage Auto 
HT Link Voltage Auto 
SB Voltage Auto 

However it's not stable, under heavy stress it may give weird errors or crash.

The lowest settings at stock speed which run 4xPrime95 + FurMark 1.8.2 stable for at least a couple of hours (no so much time to test) are:

Code: Select all

FSB 200MHz (2.300 GHz) 
CPU-NB Ratio Auto (x10) 
FSB/DRAM Ratio Auto (1:3.33) 
HT Link Speed 2000MHz (x10) 
 
CPU VDD Auto 
CPU-NB VDD Auto 
CPU Voltage 1.015V (0.976V reported in BIOS and CPU-Z) 
CPU-NB Voltage Auto 
DRAM Voltage Auto (1.584V reported in AMD OverDrive)  
NB Voltage Auto 
HT Link Voltage Auto 
SB Voltage Auto 

Just as a side note, the ***estimated*** maximum power consumptions of the cpu itself should be

<32W 2.0GHz -28.9% (~13W)
<39W 2.3GHz -13.3% (~ 6W - undervolted)
<45W 2.3GHz @stock (38.7W according to HW Monitor, 13.6W at idle)
<55W 2.7GHz +22.2% (~10W)
<70W 2.9GHz +27.3% (~15W)
<72W 3.0GHz + 3.4% (~ 2W)

while the recorded temperatures (with an about 23°C ambient) under stress goes from ~44°C (0.952V core) up to ~56°C (1.224V core): idle temps seem do not vary so much, just 1-2°C (0.728V - 0.880V).
Noteworthy to mention that those 44°C are obtained with a ~500rpm cpu fan, while the not stable 56°C are obtained with the same fan running at ~1800rpm.

Eventually the permissible areas of operation I've found for the various settings are:

CPU VDD up to 1.100V
CPU-NB VDD up to 1.100V
CPU Voltage 1.015V - 1.250V (0.976V - 1.224V reported in BIOS and CPU-Z)
CPU-NB Voltage 1.108V - 1.279V
NB Voltage 1.108V - 1.1292V
HT Link Voltage 1.202V - 1.402V

If you mind, please forgive me for any error, inaccuracy or misunderstanding. Hope to repeat soon some tests with even the power meter.

[andymcca]

Oops! Totally forgot this! Sorry!
I'm at work, but when I get home tonight I'll get right on it. Sorry for the delay!

[andymcca]

Okay, so sorry for the delay, but below are the nominal voltages my mobo gives:
CPU: 1.35V (This is for a sempron 140. Does this vary by model? I thought it did)
VDDNB: 1.1875 (This may also vary by CPU? reasoning below)
HT Voltage: 1.2V
Chipset Voltage: 1.1V

Notes:
1) I did not have separate CPU VDDNB, CPU NB and NB voltage settings. Not sure what this means for you.
2) Both CPU and VDDNB are stated as "minimum = normal - .3000V". So these values are extrapolated from the 1.05V and .8875V minimum voltages, respectively. The reason I think this VDDNB may vary by CPU is that these may be defined by some value stored on the chip? And that would explain why these two values were described in such an odd way, while all others stated fixed minimum, maximum, and nominal voltages. Any thoughts?

Edit: ps, are the values you posted in red the maximum values allowed by your motherboard? They seem universally lower than my defaults!

[quest_for_silence]

andymcca, first of all, thanks for your help.

Please note that I've added colors to my previous post in order to make it more readable.

below are the nominal voltages my mobo gives:
CPU: 1.35V (This is for a sempron 140. Does this vary by model? I thought it did)

Yes, AFAIK it does: it should be the main reason why multi cores e-series Athlon IIs are rated at 45W TDP.

VDDNB: 1.1875 (This may also vary by CPU? reasoning below)

Currently I don't know: I have a Phenom II cpu, which I'll test with this mobo next in the future, and let you know.

But, incidentally, that 1.100V is also the nominal VID of the X4 605e, as reported in BIOS (and by other monitoring softwares), so I guess it could even be cpu-related.
Maybe, if your Sempron 140's VID should be just 1.1875V, then it might be an indirect confirm of VDD settings being cpu-related.

2) Both CPU and VDDNB are stated as "minimum = normal - .3000V". So these values are extrapolated from the 1.05V and .8875V minimum voltages, respectively. The reason I think this VDDNB may vary by CPU is that these may be defined by some value stored on the chip? And that would explain why these two values were described in such an odd way, while all others stated fixed minimum, maximum, and nominal voltages. Any thoughts?

Well, I'm not sure.
Even if my MSI seems to have a wider set of adjustable voltages than your ASUS, nor I can give to chipset voltages any value lower than the reported CPU VID, neither there's any explicit indication that the related "Auto" settings can do that (as stated in your ASUS BIOS, if I've well understood).

are the values you posted in red the maximum values allowed by your motherboard? They seem universally lower than my defaults!

No, they aren't the absolute maximums I may set in the BIOS.

They are just the maximum safe values for my combo: i.e. going below or above those values - if in case - do not let me any workable further undervolting or overclocking of the combo.

To say, although I can even do POST at 286MHz FSB - iirc - reliably with the reported (red) maximum voltages, I cannot boot the OS at such frequency and I cannot do so regardless of how much voltage I may further add to those max CPU and NB/HT "red" voltages (nor I may make the system stable at lower FSB, for example 270MHz, adding juice to those red values). This is why I've stated "permissible area of safe operations I found".

Now I'm working around how to make both undervolting and overclocking.