Instructions for undervolting C-50 CPU in W500 (make W500 run a bit cooler and longer)

[maximg]

Hello everyone,

This is my first post here and I wanted to share my experiences with undervolting the W500 CPU. It is quite late now, so please excuse any typos or bad grammar.

DISCLAIMER: Use at your own risk. I do not take any responsibility of things you do to your CPUs, especially if you mess up with register values and end up overvolting and frying your CPU.

Credit for AMD undervolting goes to thierryg and StApostol from this thread: SPCR • View topic - hp dm1z undervolting and (limited) fan control, I just adapted registers values for C50.

Let's start with some background:
C50 support two P states - P0 and P1. P0 state corresponds to 1000 MHz and P1 corresponds to 800 MHz. For each state, there is an MSR register which defines CPU voltage and frequency for that state.
0xC0010064 defines voltage for P0 and 0xC0010065 defines voltage for P1. It is also possible to underclock the CPU by lowering the frequency for P0 and P1 states. For some reason, overclocking does not seem to work - CPU-Z shows higher frequency, however system performance remains the same and HWINFO32 shows that frequency is not increased.

I will dive into over/underclocking later, for now lets start with undervolting process:

1. Download RW-Everything application from RW - Read & Write - I've used portable version, RwPortableV1.5.7z;
CPU-Z (CPUID - System & hardware benchmark, monitoring, reporting) or HWInfo32 (HWiNFO32 Download) - to monitor current CPU voltage

and ORTHOS (Orthos - Overclock.net - Overclocking.net) or Prime95 (Free Software - GIMPS) for stability tests.

2. Unzip or install RW application. I've placed it to C:\UTILS\RW and will be referring to this path in this guide.
3. create new file called read.ro in directory where you placed RW application. Put following lines into it:

>cpu 1
>rdmsr 0xc0010064
>rdmsr 0xc0010065
>cpu 2
>rdmsr 0xc0010064
>rdmsr 0xc0010065
>RwExit

rdmsr 0xc0010064 reads MSR register data for P0 state and rdmsr 0xc0010065 reads register data for P1.

4. Start command line as Administrator - you need to run as admin, otherwise it would not be able to read/write to MSR registers. Go to RW directory (C:\utils\rw in my case). Run following command:

rw /Command=read.ro /Logfile=initial.txt

this would dump current MSR registers data for your C50 into results.log file. These registers contains configuration data for P0 and P1 states of AMD C-50. P0 corresponds to 1000 MHz frequency and P1 corresponds to 800 Mhz.
I am not sure if everyone's CPU is running on the same voltage, but mine was running at 1.0625 volt at 1 GHz and at 0.9375 volt at 800 Mhz.

Current CPU = CPU1
Read MSR 0xC0010064 : High 32bit(EDX) = 0x8000029C, Low 32bit(EAX) = 0x00004E30
63    56 55    48 47    40 39    32 31    24 23    16 15     8 7      0
10000000-00000000-00000010-10011100-00000000-00000000-01001110-00110000
Read MSR 0xC0010065 : High 32bit(EDX) = 0x8000026F, Low 32bit(EAX) = 0x00006240
63    56 55    48 47    40 39    32 31    24 23    16 15     8 7      0
10000000-00000000-00000010-01101111-00000000-00000000-01100010-01000000
Current CPU = CPU2
Read MSR 0xC0010064 : High 32bit(EDX) = 0x8000029C, Low 32bit(EAX) = 0x00004E30
63    56 55    48 47    40 39    32 31    24 23    16 15     8 7      0
10000000-00000000-00000010-10011100-00000000-00000000-01001110-00110000
Read MSR 0xC0010065 : High 32bit(EDX) = 0x8000026F, Low 32bit(EAX) = 0x00006240
63    56 55    48 47    40 39    32 31    24 23    16 15     8 7      0
10000000-00000000-00000010-01101111-00000000-00000000-01100010-01000000

We will be changing digits 5 and 6 in EAX value for each register - these are defining CPU voltage. Note that in order to lower the voltage, we will need to increase the value.

5. Copy/paste values from results.log to normal.rw file using template below, replacing columns 2 and 3 with EDX and EAX values from initial.txt
- this will be the configuration file to roll back to original MSR values. My normal.rw file looks like this:

>cpu 1
>wrmsr 0xc0010064 0x8000029C 0x00004E30
>wrmsr 0xc0010065 0x8000026F 0x00006240
>cpu 2
>wrmsr 0xc0010064 0x8000029C 0x00004E30
>wrmsr 0xc0010065 0x8000026F 0x00006240
>RwExit

Your EAX values may be slightly different if your CPU had different initial voltage (I don't know if all C-50 CPUs are equal).

6. Now create another copy of normal.rw file (I've called it low4.rw). We will be using it to find the lowest voltage your CPU can sustain.

7. Repeat following: Edit low4.rw and increase values 4E and 62 (refer to the table below for the actual voltage). Please remember that values should be even (otherwise you will downclock your CPU to ~200MHz).
Save low4.rw and load new values into MSR registers using following command:

rw.exe /Command=low4.rw

8. Run orthos or prime95 stress test to ensure that your CPU is stable at this frequency. If it is stable, repeat step 7 increasing VID values even more. If it fails (or computer hangs), power it off by holding power key for few seconds and then power it on and return to last stable VID.
The maximal stable voltage values for my W500 were 66 and 7A, so my CPU is running at 0.9125 volt at 1GHz and 0.7875 volt at 800MHz. You can try jumping to
VID 60 for P1 and VID 74 for P2 to see if it works for you and then work from there.

>cpu 1
>wrmsr 0xc0010064 0x8000029C 0x00006630
>wrmsr 0xc0010065 0x8000026F 0x00007A40
>cpu 2
>wrmsr 0xc0010064 0x8000029C 0x00006630
>wrmsr 0xc0010065 0x8000026F 0x00007A40
>RwExit

9. Once you are satisfied with your settings, we will need to make sure MSR registers are updated after each startup/wake up cycle. We will create a scheduled task to run on every startup/system unlock.
The easiest way to create the task is to import Undervolting.xml attached with following command:

schtasks /Create /XML Undervolting.xml /TN Undervolting

and then just edit the path to rw.exe and "Start in" path in Actions tab, or you can create it manually:

9.1 Open task scheduler and create a new task. In General tab, enter task name, select "Run whether user is logged on or not", select "Do not store password. The task will only have access to local resources"
and "Run with highest privileges".

9.2 On Triggers tab, add following triggers: "At Startup", "On Connection to user session" and "On workstation unlock".
9.3 On Actions tab, add a new "Start a program" action. For Program script, enter [Your PATH to RW]\rw.exe (in my case it was c:\utils\rw\rw.exe).
For arguments, enter /Command=low4.rw /Logfile=log.txt
For Start in, enter the path to RW.EXE program (c:\utils\rw in my case).
In Conditions tab, uncheck "Start the task only if computer is on AC power".

10. Save this task and reboot your W500. Use CPU-Z or HWINFO to monitor if CPU voltages are changed. Please note that it may take up to 1 minute for this scheduled task to run, so wait for some time before you assume that it is not working at all.


Power savings:
When running ORTHOS load with W500 plugged in with fully charged battery and minimal screen brightness, my Kill A Watt device is showing 10W power consumption; with voltage lowered to 0.9125 it shows about 9W. HW Monitor shows that CPU temperature is about 4 degrees lower. Unfortunately this underclocking is not affecting GPU, so anything that utilizes GPU would not benefit from lower power consumption.

Voltage/VID values:

1.3000	28
1.2875	2A
1.2750	2C
1.2625	2E
1.2500	30
1.2375	32
1.2250	34
1.2125	36
1.2000	38
1.1875	3A
1.1750	3C
1.1625	3E
1.1500	40
1.1375	42
1.1250	44
1.1125	46
1.1000	48
1.0875	4A
1.0750	4C
1.0625	4E
1.0500	50
1.0375	52
1.0250	54
1.0125	56
1.0000	58
0.9875	5A
0.9750	5C
0.9625	5E
0.9500	60
0.9375	62
0.9250	64
0.9125	66
0.9000	68
0.8875	6A
0.8750	6C
0.8625	6E
0.8500	70
0.8375	72
0.8250	74
0.8125	76
0.8000	78
0.7875	7A
0.7750	7C
0.7625	7E
0.7500	80
0.7375	82
0.7250	84
0.7125	86
0.7000	88

[excalibur1814]

Although I'm not planning on actually implementing the process I still appreciate the time you've taken to post; I also look forward to others having a go and posting their results.

Thanks!

[papi]

Back in the days when I was running AMD desktops my favorite tool for undervolting and underclocking was CrystalCPUID. I'm not sure if it would work with the C-50.

Just a thought: Since there are only two CPU states I don't think playing with the clock frequency would buy you much as 800MHz is likely to be too low for most work. I think the best you can do is to find the lowest vcore that would work at each of these frequencies (800MHz and 1GHz).

I don't know how undervoltable the C-50 is but desktop AMD processors were very undervoltable. I was running an AMD X2 (Brisbane) based systems with such a low idle power consumption (under 30W) that they were only beaten years later when the Zacate (the desktop version of the C-50) came out.

[excalibur1814]

I constantly run my W500 at max CPU 10% and don't have any negative things going on (Then again I've tweaked it to an inch of it's life)

[papi]

With a low power CPU like the C-50, I think trying to get more battery life out of it is like wringing water out of stone.

Having said that, if someone can undervolt this baby to 0.8V @ 1GHz (what I was able to do with a desktop AMD X2) then I'll jump on the bandwagon.

[Syberia]

I'd be more interested in overclocking, the GPU is powerful for what it is but the CPU seems a bit weak.

[pkirill]

Hi Maximg, outstanging guide, thanks !!!

[e-schreiber]

This is my first post here and I wanted to share my experiences with undervolting the W500 CPU. It is quite late now, so please excuse any typos or bad grammar.

I don't have a W500, but I must congratulate you for the time and effort you've put into this guide!

[gljvd@aim.com]

Very nice , how much more battery life does that equal.

The z-01 which is new verison of the c-50 uses just 5.9w instead of 9w . So i'm wondering how the battery life is affected.

[cylent]

i think this program does the job easier; PhenomMsrTweaker: Cool & Quiet customized
and then theres also this; http://code.google.com/p/brazostweaker/

also theres a long thread about this issue here:
AMD C-50 CPU and 6250 GPU performance(Acer 522 review)