Overclocking

Contents

[edit] Reminders

This page is about overclocking and undervolting the N900. For the N8x0 see this thread on talk.maemo.org

Overclocking is discussed in this thread. Benchmark results can be found here. If you're more interested in power saving read this.

This guide focuses on kernel-power v50 and above, as it introduces improvements in stability and maximum supported frequency for SmartReflex, making it highly desirable for a Maemo system that is overclocked 24/7.

[edit] Warnings

  • Overclocking WILL VOID YOUR WARRANTY. Your warranty does not cover running the device beyond the specifications.
  • The lifetime of your device WILL get reduced as a result of wikipedia:Electromigration electromigration
  • Your device might not perform properly - bizarre bugs and corruption may result from the CPU being physically unable to cope with higher frequencies (see the next point)
  • All devices are not made equal - some may be able to handle 1.15GHz daily just fine, while some may be unstable even at 720MHz.
  • You do it at your own responsibility. No whining afterwards. If you're unsure, don't do it.
  • Nokia's overclocking warning: 500 MHz is the normal frequency. Everything above is not good for your device, even with the stock kernel.
  • Igor Stoppa's warning and comment
  • chip vendors specs

[edit] Lifetime, warranty and damage

  • The expected lifetime all devices is limited due to wear.
  • It is usually much longer (several years) than the warranty period, so that even with heavy use within the specifications it would not fail before warranty ends.
  • With overclocking users may see considerable speed improvements and lower latency in user experience which could extend the actual lifetime (of being used) as the device could keep up with the newer models.
  • Excessive overclocking with stock voltages is definitely bad for most components in your device, especially if the device is continuously locked at high frequencies with high load (see TI specs).
  • Specifications give guarantees for the worst-case scenarios that are covered by the warranty. The best-case scenario may be different for every device but is not covered by warranty.
  • However, there is an open debate whether mild (<40%) overclocking with lower voltages (undervolting) does actually harm or is even less harmful than the stock settings. See #Undervolting and voltage tables for an explanation why undervolting in fact won't help anything due to chip using SmartReflex Technology (which can not be disabled).
  • Evidence for or against damages (esp. with undervolting) in the N900 is currently absent and will probably only be available when the device is no longer on the market. Or you decide to acquire thorough electronics engineer's understanding of the issue, and study TI's papers regarding SmartReflex™ and how it works - then all the evidence for damage positively done is there already.
  • Therefore, if you are unsure and you want to avoid potential damages, do not overclock!

[edit] Overclocking, bugzilla & errors

  • Running a device overclocked for long periods of time could produce unwanted side effects, even persisting ones that won't revert when overclocking is stopped. If you are experiencing errors following overclocking and intend to report those errors to talk.maemo.org or bugzilla, please consider the following :
    • Errors induced by overclocking will not always appear to be as such.
    • It will be considered a good idea to reproduce your error / problem on a device which has never been overclocked AT ALL, before proceeding with actions regarding your problem.
    • In the event you have decided to file a bug report or open a thread about your problem, please add a note to that report, mentioning that you are or previously were in fact running your device overclocked. Please also provide details about the period and amount of overclocking used.
  • The reason for these requirements is that there are many problems pending for developer's attention. It is a huge waste of time to try and trace down an error without knowing all the facts, just to find out in the end that the particular problem was caused by a damaged hardware. If the developers know about it, they can take it into account and won't rule out a 1+1=3 problem on the reporter's device during their analysis.

[edit] Additional information and hints

  • The stock Nokia kernel uses the following frequencies: 250, 500, 550 and 600 MHz.
  • The CPU does NOT IDLE at the lowest frequency (250 MHz) but it SLEEPS at 0 MHz! Thus, reducing the lowest frequency would not reduce power consumption. It is only activated during low workload and may actually consume more power than a higher frequency, as it takes more time to go back to sleep/idle state.
  • Setting the lowest frequency to 125 MHz does NOT improve battery life. In fact, many people noticed worse battery life, instability and worse responsiveness,
  • The Phone app is closed-source and broken. During a phone call, the device's frequency is locked to 600MHz. This may be a bug, and it affects all kernels for Fremantle. After a phone call, it sets the maximum to 600 Mhz and the minimum to 250 MHz (or 125 MHz if available) regardless of the frequencies you have set. There are some workarounds present in kernel-power, however the bug may still occasionally manifest.
  • When connected via USB the device locks the minimum frequency to 500 Mhz.
  • By default the device is configured to use 125 MHz as the lowest frequency but it not enabled in the kernel pmconfig bug
  • The warning
    WARNING: at arch/arm/mach-omap2/clock34xx.c:443 omap3_noncore_dpll_set_rate+0x28c/0x2dc()
    in the kernel logs (dmesg) only happens if the invalid 800 MHz frequency was selected. Ignore it.
  • EvilJazz had photoshopped a picture of a device being overclocked 1.7GHz. It's a prank!
  • The internal temperature sensor may be read by using the command "cat /sys/devices/platform/omap34xx_temp/temp1_input"
  • Note that the system does not have an on-die temperature sensor, and the actual CPU temperature may be higher or lower than the reading.

[edit] Installing a modified kernel

Overclocking and undervolting require installation of a custom kernel. There are two types of kernels:

[edit] Kernel-Power (recommended)

kernel-power, developed by Titan and maintained by Pali. They are compatible with PR1.2 and PR1.3, contain lots of additional features (IPv6, NAT etc) and bugfixes. In addition, they include a large set of possible frequencies (125 MHz-1.15 GHz) which can be manually set and tested without flashing a new kernel.

The defaults are set to the standard 250-600 MHz range.

This guide recommends using kernel-power v50, which at the time of writing is available in the extras catalog. Newer, more experimental kernels may be available through extras-testing or extras-devel.

[edit] Installing from the repositories

  1. Open the Application Manager
  2. Go to the "System" section, and install the package kernel-power-settings. This automatically pulls in the rest of kernel-power as dependencies.
  3. After successful installation, reboot the device.

[edit] Lehto's Kernel and other legacy kernels

Modified PR1.1 kernels by Lehto and others. The only difference from the stock Nokia kernel is the change of the available hardcoded frequencies.

[edit] Flashing from X Terminal

  • do a backup, have a PC nearby and know you are able to flash the N900 with flasher-3.5 - just in case
  1. Launch X Terminal, then type
    sudo gainroot
  2. Type:
    softupd -vv -s --local
    (that is a double v)
  3. Open new terminal
  4. Type:
    flasher --local -f -k <kernel_zimage_file_with_path>
  5. You'll see the flashing (takes some time)
  6. Type "sync" to save changes
  7. Type "reboot" and enter to restart
  8. Test out your phone as usual. (Apps, browser, camera, phone etc etc)
  9. If any abnormal events occur frequently (crash, hang, screen corruption etc), turn it off, flash it to a slower kernel and test again.

[edit] Reverting to the Stock Kernel

If you want to revert to the stock Nokia kernel, execute:

apt-get install --reinstall kernel kernel-flasher

in X Terminal.

[edit] Fixing the version information

If your version information got lost (control panel -> version) you can fix it by reinstalling the package that is listed with:

dpkg -l "mp-fremantle*"

for example, "mp-fremantle-generic-pr" (for some firmwares 002 or 003 instead of generic) and then execute:

apt-get install --reinstall mp-fremantle-generic-pr

[edit] Overclocking

Once you have installed kernel-power, you are ready to start overclocking.

  1. List available frequencies ("active frequencies")
     sudo kernel-config show 
  2. Select the lowest and highest frequencies to be used from the list of active frequencies, The kernel will use all active frequencies between and including those you selected.
  3. The following command will set the frequencies to stock:
     sudo kernel-config limits 250 600 
  4. The following command will set the maximum to the highest supported by SmartReflex. (Note that SmartReflex in kernel-power v50 only works with frequencies up to 900MHz.)
     sudo kernel-config limits 250 900 
  5. At this point, you should test system stability by launching a few programs, browsing JavaScript-heavy webpages, and playing a movie.
  6. Should you encounter no reboots, you can save your overclocking profile.
     sudo kernel-config save myprofile 
  7. You can now proceed to set your kernel profile as the default, to be loaded automatically at startup.
     sudo kernel-config default myprofile 

[edit] Undervolting

[edit] SmartReflex

[edit] Rationale

Before kernel-power v50, one would normally set voltages per frequency in a configuration file, which required manual testing to determine the lowest voltages possible for a specific frequency. This may result in reboots if the voltage was not set high enough to account for the CPU's power usage at full loads, or power wastage if the voltages were set higher than what is needed for light loads at a certain frequency. SmartReflex is a technology which automatically regulates the voltage used for the entire SoC, automatically adapting to lower voltages during light use and increase them during heavy use.

[edit] Automatic Undervolting

Once kernel-power v50 or higher is installed, enabling it is a matter of doing the following:

  1. Make a folder for your kernel profiles
     mkdir -p ~/.kernel 
  2. Copy a sane profile to your kernel profile folder
     cp /usr/share/kernel-power-settings/default ~/.kernel/myprofile 
  3. Edit the profile to enable SmartReflex
     nano ~/.kernel/myprofile 
  4. Look for the lines:
     SMARTREFLEX_VDD1=0 SMARTREFLEX_VDD2=0
  5. Edit them to the following:
    SMARTREFLEX_VDD1=1 SMARTREFLEX_VDD2=1
  6. Save the file by pressing Ctrl+X, and confirm with Y then press Enter.
  7. Test the profile
     sudo kernel-config load myprofile 
  8. At this point, you'd want to stress the CPU a bit. Launch a few programs, visit JS-heavy websites, etc.
  9. If the device does not reboot and you feel safe using the profile, set it as the default.
     sudo kernel-config default myprofile 
  10. Congratulations, the kernel is now doing all the work for you.

[edit] Manual Undervolting (Legacy)

See: http://talk.maemo.org/showpost.php?p=628839&postcount=81

Extract from the post:

CPU power consumption (without constants) = leakage + capacitance + switching = voltage^2 + frequency + (voltage^2 * frequency)

One factor reducing CPU lifetime is the current it is running with dynamic frequency scaling.

CPU dynamic power consumption = capacitance * frequency * voltage^2

As can be seen from the formula, lower voltage plays greater part in CPU consumption than frequency. By reducing the voltage the damage of overclocking can be reduced and the battery life time extended. Alas, this claim only holds true for architectures not regulating the real voltage and current in special on chip regulators, like OMAP is known to do for almost every gate in their CPU and other SoC function blocks. TI calls this feature SmartReflex™ and lowering the voltage applied to the whole SoC, like suggested here, only reduces the voltage drop across these regulators, thus no positive effect on electromigration damage caused by overclocking is to be expected.

[edit] Calculating Voltages

According to these calculations, the voltage can be varied in steps of 0.0125 V with values 0-72. The formula is (with x being the kernel parameter value):

V = x * 0.0125 + 0.6

Examples:

Lowest voltage (x = 0):   0  * 0.0125 + 0.6 = 0     + 0.6 = 0.6 V
Highest voltage (x = 72): 72 * 0.0125 + 0.6 = 0.9   + 0.6 = 1.5 V
Random voltage (x = 38):  38 * 0.0125 + 0.6 = 0.475 + 0.6 = 1.075 V

[edit] Voltage Table

  • V²/us for frequencies 720 and 805 need to be recalculated.
  • Bolded steps indicate the first frequency in the kernel which needs overvoltage. All frequencies after it are overvolted.
Frequency Nokia LV ULV XLV ideal starving
0 MHz 30 30 25 30 30 22
0.975V, 0.000 V²/us 0.975V, 0.000 V²/us 0.912V, 0.000 V²/us 0.975V, 0.000 V²/us 0.975V, 0.000 V²/us
125 MHz 30 30 25 20 30 22
0.975V, 288.906 V²/us 0.975V, 118.828 V²/us 0.912V, 103.968 V²/us 0.975V, 118.828 V²/us 0.975V, 118.828 V²/us
250 MHz 38 38 25 30 30 28
1.075 V, 118.828 V²/us 1.075 V, 118.828 V²/us 0.912V, 207.936 V²/us 0.975V, 237.656 V²/us 0.975V, 237.656 V²/us
500 MHz 48 48 33 33 30 29
1.200 V, 720.000 V²/us 1.200 V, 720.000 V²/us 1.012V, 512.072 V²/us 1.012V, 512.072 V²/us 0.975V, 475.312 V²/us
550 MHz 54 48 38 38 33 32
1.275 V, 894.094 V²/us 1.200 V, 792.000 V²/us 1.075V, 635.594 V²/us 1.075V, 635.594 V²/us 1.012V, 563.279 V²/us
600 MHz 60 54 38 38 38 34
1.350 V, 1093.500 V²/us 1.275 V, 975.375 V²/us 1.075V, 693.375 V²/us 1.075V, 693.375 V²/us 1.075V, 693.375 V²/us
720 MHz 54 45 45 45 42
1.275 V, 1137.938 V²/us 1.163 V, 1014.427 V²/us 1.163 V, 1014.427 V²/us 1.163 V, 1014.427 V²/us
805 MHz 54 48 48 48 45
1.275 V, 1316.756 V²/us 1.200 V, 1166.400 V²/us 1.200 V, 1166.400 V²/us 1.200V, 1166.200 V²/us
850 MHz 54 48 48 48 46
1.275 V, 1381.781 V²/us 1.200 V, 1224.000 V²/us 1.200 V, 1224.000 V²/us 1.200V, 1224.000 V²/us
900 MHz 54 54 54 54 49
1.275 V, 1463.062 V²/us 1.275V, 1463.062 V²/us 1.275V, 1463.062 V²/us 1.275 V, 1463.062 V²/us
950 MHz 54 54 54 54 52
1.275 V, 1544.344 V²/us 1.275 V, 1544.344 V²/us 1.275 V, 1544.344 V²/us 1.275 V, 1544.344 V²/us
1000 MHz 60 60 60 60 55
1.350 V, 1822.500 V²/us 1.350 V, 1822.500 V²/us 1.350 V, 1822.500 V²/us 1.350 V, 1822.500 V²/us
1100 MHz 72 72 72 72 63
1.500 V, 2475.000 V²/us 1.500 V, 2475.000 V²/us 1.500 V, 2475.000 V²/us 1.500 V, 2475.000 V²/us
1150 MHz 72 72 72 72 69
1.500 V, 2700.000 V²/us 1.500 V, 2700.000 V²/us 1.500 V, 2700.000 V²/us 1.500 V, 2700.000 V²/us

[edit] Useful scripts

[edit] Analyze kernel system frequency use percentage

Written by rooted

I've stopped the development of this script and I hope someone will make use of the code. I hope titan includes it in "kernel-config show" or "kernel-config debug". -rooted

This script prints percentage of frequencies (states) used and some additional info useful for posting on the forum (debugging). It displays all frequencies, works with all kernels and it is not affected by the bug which resets minimum frequency after phone call.

Temperature may not be listed if you don't have module bq27x00_battery installed or enabled. Also kernel-power version is not listed if you don't use titan's kernel.

#!/bin/sh
 
idlefreq=`awk '{if ($2 > 0) print $1}' /sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_state | tail -n 1`
tis1=`awk '{sum += $2} END {print sum}' /sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_state`
tis2=`awk '$1 == "'"$idlefreq"'" {idle = $2} {sum += $2} END {print sum-idle}' /sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_state`
 
echo -e "
TIME_IN_STATE ANALYSING SCRIPT
By rooted (maemo.org)
Revision 7
wiki.maemo.org/Overclocking
 
 
FREQUENCY\tUSED\t\tWHEN BUSY\n"
awk '
{if ($1 >= 1000000)                 printf ("%.0f MHz\t",$1/1000); else printf ("%.0f MHz\t\t",$1/1000)}
{if ($2 == 0)                       printf "unused";               else printf ("%.1f %\t\t",($2*100)/"'"$tis1"'")}
{if ($2 == 0 || $2/"'"$tis2"'" > 1) printf "\n";                   else printf ("%.1f %\n",($2*100)/"'"$tis2"'")}
' /sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_state
 
echo -e "
Kernel:                  `uname -r`
kernel-power:            `dpkg -l kernel-power | awk '$2 == "kernel-power" {print $3}'`
kernel-power-settings:   `dpkg -l kernel-power-settings | awk '$2 == "kernel-power-settings" {print $3}'`
Uptime:                  `uptime | sed -e 's/.*p *//' -e 's/, l.*//' -e 's/  / /'`
Load:                    `uptime | sed 's/.*e: //'`
Boot reason:             `cat /proc/bootreason`
Temperature:             `cat /sys/class/power_supply/bq27200-0/temp` degrees C\n"

Output example:

TIME_IN_STATE ANALYSING SCRIPT
By rooted (maemo.org)
Revision 7
wiki.maemo.org/Overclocking


FREQUENCY       USED            WHEN BUSY

1150 MHz        unused
1100 MHz        unused
1000 MHz        unused
950 MHz         unused
900 MHz         unused
850 MHz         unused
805 MHz         4.5 %           58.9 %
750 MHz         0.0 %           0.4 %
700 MHz         0.0 %           0.3 %
600 MHz         0.3 %           3.4 %
550 MHz         0.0 %           0.5 %
500 MHz         2.8 %           36.5 %
250 MHz         92.4 %
125 MHz         unused

Kernel:                  2.6.28.10power37
kernel-power:            2.6.28-maemo37
kernel-power-settings:   0.11
Uptime:                  56 min
Load:                    0.25, 0.12, 0.09
Boot reason:             pwr_key
Temperature:             31 degrees C

[edit] Analyze kernel system frequency use percentage, including idle mode stats

Written by ArbitRabbit

The following script will show the current frequency and statistics for each state, including time spent in idle mode when the CPU is actually sleeping. This script works with the special frequency handling in Titan's kernel.

To run this script as user and be able to set the frequencies you will need to install "rootsh" via apt-get.

scheduler_stats.sh

#!/bin/sh
awk '{print "\nCurrent frequency: "$1/1000" MHz\n"}' /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq
awk '{print "Minimum frequency: "$1/1000" MHz\n"}' /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
awk '{print "Maximum frequency: "$1/1000" MHz\n"}' /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
 
tis1=`awk '{SUM += $2} END {printf("%.0f",SUM/1000)}' /sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_state`
 
idle0=`awk '{printf ("%.0f",$1/1000)}' /sys/devices/system/cpu/cpu0/cpuidle/state0/time`
 
idle1=`awk '{printf ("%.0f",$1/1000)}' /sys/devices/system/cpu/cpu0/cpuidle/state1/time`
 
idle2=`awk '{printf ("%.0f",$1/1000)}' /sys/devices/system/cpu/cpu0/cpuidle/state2/time`
 
idle3=`awk '{printf ("%.0f",$1/1000)}' /sys/devices/system/cpu/cpu0/cpuidle/state3/time`
 
totaltime=$(($idle0+$idle1+$idle2+$idle3+$tis1))
echo -e "FREQUENCY\tUSED"
SUM=0
awk '
       {
               printf (($1/1000)" MHz \t");
               if ($2 == 0)
               {
                       printf "0 %\n";
               }
               else {
                       SUM+=$2;
                       printf("%.3f %\n",($2/10)/"'"$totaltime"'");
                       }
       }
       END{
       printf ("Time spent in idle mode is %2.2f %\n",(1-((SUM/1000)/"'"$totaltime"'"))*100);
       }' /sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_state
echo ""

Sample Output

Current frequency: 500 MHz

Minimum frequency: 500 MHz

Maximum frequency: 810 MHz

FREQUENCY       USED
1200 MHz        0 %
1100 MHz        0 %
1000 MHz        0 %
950 MHz         0 %
900 MHz         0 %
850 MHz         0 %
810 MHz         0.000 %
750 MHz         0.000 %
700 MHz         0.000 %
600 MHz         0.000 %
550 MHz         0.000 %
500 MHz         0.010 %
Time spent in idle mode is 99.99 %

Known Bugs: Requires the Phone to be booted for an hour or so before it results in decent stats.

[edit] Combined helper script

Written by EvilJazz

The following script will show the current frequency and statistics. It also accepts two optional parameters that will set the max and/or min frequencies (in MHz unit). Calling the script without these parameters will not set the new clocking. Instead it will just show the current frequencies and statistics.

This script works with the special frequency handling in Titan's kernel.

To run this script as user and be able to set the frequencies you will need to install "rootsh" via apt-get.

overclock.sh [max freq] [min freq]
#!/bin/sh
max=${1}000
min=${2}000
 
# Handle and rewrite special cases in Titan's kernel...
[ "$max" == "600000" ] && max=599000
[ "$min" == "125000" ] && min=124999
 
if [ $(id -u) -ne 0 ]; then
  [ "$max" != "000" ] && echo "echo $max > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq" | sudo gainroot
  [ "$min" != "000" ] && echo "echo $min > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq" | sudo gainroot
else
  [ "$max" != "000" ] && echo $max > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
  [ "$min" != "000" ] && echo $min > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
fi
 
awk '{printf("\nCurrent frequency: %7s MHz\n", $1/1000)}' /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq
awk '{printf("Minimal frequency: %7s MHz\n", $1/1000)}' /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
awk '{printf("Maximal frequency: %7s MHz\n\n", $1/1000)}' /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
 
sum=$(awk '{SUM += $2} END {print SUM}' /sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_state)
awk '{printf("%7s MHz: %5.1f % (%8d)\n", ($1/1000), ($2 * 100)/"'"$sum"'", $2)}' /sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_state
echo

Output example:

~ $ ./overclock.sh 600 250

Current frequency:     250 MHz
Minimal frequency:     250 MHz
Maximal frequency:     599 MHz

   1200 MHz:   0.0 % (       0)
   1100 MHz:   0.0 % (       0)
   1000 MHz:   0.0 % (       0)
    950 MHz:   0.0 % (       0)
    900 MHz:   0.2 % (     271)
    850 MHz:   0.0 % (       0)
    810 MHz:   0.0 % (       0)
    750 MHz:   0.0 % (       0)
    700 MHz:   0.0 % (       0)
    600 MHz:   9.0 % (   13663)
    550 MHz:   0.5 % (     701)
    500 MHz:  15.4 % (   23379)
    250 MHz:  75.0 % (  114021)
124.999 MHz:   0.0 % (       0)

[edit] Underclock/Overclock when phone is locked/unlocked

Written by Fecn

When locked, the limits are changed to 250/500 Mhz to save power - I don't need my phone to be fast when it's sitting there doing nothing. (I did try with 125 Mhz as minimum but it caused an unresponsive touchscreen during incoming phone calls and alarms)

When unlocked, the limits are set for overclocking, with the max speed determined by the temperature (1150 Mhz is stable on my phone - your mileage may vary - adjust scripts as required)

You need the dbus-scripts package installed for this to work. You also need to add bq27x00_battery to your /etc/modules so that it is loaded at boot time - it needs to be loaded to be able to read the temperature.

Note by --joerg_rw 18:03, 2 August 2010 (UTC): Which temperature are you trying to base that on? Anyway the bq27200 temperature is vastly useless for this purpose, as it is the die (chip) temperature of the battery charge gauge, and neither related to CPU die temperature, nor to battery cell temperature.

We use the dbus-signalling to follow what the phone is doing and fire off scripts to change the limits accordingly.

Create the following two 1-line files inside /etc/dbus-scripts.d/ (before you need to install the dbus-scripts package)

Filename: /etc/dbus-scripts.d/locked 
/usr/local/bin/underclock * * com.nokia.mce.signal tklock_mode_ind locked

Filename: /etc/dbus-scripts.d/unlocked
/usr/local/bin/overclock * * com.nokia.mce.signal tklock_mode_ind unlocked

... and then create corresponding scripts that they call inside /usr/local/bin/ ( don't forget to chmod them to executable )

Filename: /usr/local/bin/underclock 
#!/bin/sh
kernel-config limits 250 500

Filename: /usr/local/bin/overclock  
#!/bin/sh
TEMP=`cat /sys/class/power_supply/bq27200-0/temp`
echo "Temp is :" $TEMP "C"
MAXSPEED="1150"
if [ $TEMP -gt "38" ] ; then MAXSPEED="1000" ; fi
if [ $TEMP -gt "40" ] ; then MAXSPEED="950" ; fi
if [ $TEMP -gt "43" ] ; then MAXSPEED="850" ; fi
if [ $TEMP -gt "45" ] ; then MAXSPEED="750" ; fi
if [ $TEMP -gt "47" ] ; then MAXSPEED="600" ; fi
echo "Setting max as :" $MAXSPEED "Mhz"

kernel-config limits 250 $MAXSPEED

You'll need to restart dbus-scripts for it to see the new configs. I found that the scripts in init.d weren't too good at doing this, so had to kill it manually each time.

If you want to scale your processor speed according to battery capacity in addition to temperature, use an overclock script something like the following:

Filename: /usr/local/bin/overclock
#!/bin/sh
TEMP=`cat /sys/class/power_supply/bq27200-0/temp`
echo "Temp is:" $TEMP "C"
MAXSPEED="1150"
if [ $TEMP -gt "38" ] ; then MAXSPEED="1000" ; fi
if [ $TEMP -gt "40" ] ; then MAXSPEED="950" ; fi
if [ $TEMP -gt "43" ] ; then MAXSPEED="850" ; fi
if [ $TEMP -gt "45" ] ; then MAXSPEED="750" ; fi
if [ $TEMP -gt "47" ] ; then MAXSPEED="600" ; fi

BATTERY=`cat /sys/class/power_supply/bq27200-0/capacity`
echo "Battery is:" $BATTERY "% full"
MAXSPEEDTWO="1150"
if [ $BATTERY -lt "60" ] ; then MAXSPEEDTWO="850" ; fi
if [ $BATTERY -lt "40" ] ; then MAXSPEEDTWO="600" ; fi
if [ $BATTERY -lt "25" ] ; then MAXSPEEDTWO="500" ; fi

if [ $MAXSPEEDTWO -lt $MAXSPEED ] ; then MAXSPEED=$MAXSPEEDTWO ; fi

echo "Setting max as:" $MAXSPEED "Mhz"

kernel-config limits 250 $MAXSPEED