Before Starting


1. linux-source-2.6.?? (linux-source-2.6.?? should be the kernel version you have.)
Clean installed Debian Etch 4.0 r3 "debian-40r3-i386-CD-1.iso" is linux-source-2.6.18

2. Download the linuxphc patch of the speedstep-centrino module.
https://www.dedigentoo.org/bdz/linux-phc/
linux-phc-0.3pre1
Actually this patch support acpi_cpufreq ,speedstep-centrino ,powernow-k8 by patching /arch/i386/kernel/cpu/cpufreq/Kconfig inside the linux-source-2.6.??.

It supported is wroted inside the documentation clearly.
Kernel flavor | Kernel version | Patch | Status
================================================== =======
Vanilla | 2.6.15 | vanilla-2.6.15 | Clean
|------------------------------------------
| 2.6.16 | vanilla-2.6.16 | Clean
|------------------------------------------
| 2.6.17 | vanilla-2.6.17 | Clean
|------------------------------------------
| 2.6.18 | vanilla-2.6.18 | Clean
|------------------------------------------
| 2.6.19 | vanilla-2.6.19 | Clean
|------------------------------------------
| 2.6.20 | vanilla-2.6.20 | Clean
|------------------------------------------
| 2.6.21 | vanilla-2.6.21 | Clean
================================================== =======
CK | 2.6.17-ck1 | vanilla-2.6.17 | Clean
|------------------------------------------
| 2.6.18-ck1 | vanilla-2.6.18 | Clean
================================================== =======
Gentoo | 2.6.15-r8 | vanilla-2.6.15 | Clean
|------------------------------------------
| 2.6.16-r13 | vanilla-2.6.16 | Clean
|------------------------------------------
| 2.6.17-r8 | vanilla-2.6.17 | Clean
|------------------------------------------
| 2.6.18 | vanilla-2.6.18 | Clean
|------------------------------------------
| 2.6.19 | vanilla-2.6.19 | Clean
|------------------------------------------
| 2.6.20 | vanilla-2.6.20 | Clean
================================================== =======
Debian Etch | 2.6.18-3-686 | vanilla-2.6.18 | Clean
================================================== =======
Ubuntu | 2.6.15-26.45 | ubuntu-2.6.15 | Clean
|------------------------------------------
| 2.6.17-5.15 | ubuntu-2.6.17 | Clean
================================================== =======
This is i worry about this patch is only for 2.6.18-3-686 in etch but I only have 2.6.18-6-686 since this is newer.
So i am try to die hard or live free, and finnally this howto page have happly came out.

3. build-essentials

4. Extra package needed for boot script.
sysfsutils
cpufrequtils


Pratical
1. If you have preview load the speedstep-centrino module, comment speedstep-centrino and cpufreq* ,if don't want try to investigate before follow this Howto.

debian:/home/l# gedit /etc/modules
#speedstep-centrino
#cpufreq_conservative
#cpufreq_ondemand
#cpufreq_userspace
#cpufreq_powersave
#cpufreq_stats
Restart computer.

2 Get the linux source
Application -> Accessories -> Root Terminal
debian:/home/l/# apt-get install linux-source-2.6.18
Changing directory
debian:/home/l/# cd /usr/src
Untar linux source
debian:/usr/src# tar -xjf linux-source-2.6.18.tar.bz2
Changing directory
debian:/usr/src# cd linux-source-2.6.18
3 Patching the linux source
Untar linux-phc-0.3pre1 downloaded from web on desktop

Coping the patch from the linuxphc patch from the desktop to linux source.(Notice the /home/l/* should be yours.)
debian:/usr/src/linux-source-2.6.18# cp /home/l/Desktop/linux-phc-0.3.0-pre1/kernel-patch/linux-phc-0.3.0-pre1-kernel-vanilla-2.6.18.patch .
Patching the linux source.
debian:/usr/src/linux-source-2.6.18# patch -p1 < linux-phc-0.3.0-pre1-kernel-vanilla-2.6.18.patch
Copy old config file.
debian:/usr/src/linux-source-2.6.18# cp /boot/config-$(uname -r) .config
4 Prepare and complie the module.
Prepare the kernel
debian:/usr/src/linux-source-2.6.18# make oldconfig
(If prompt something , answer 'y' for all)

debian:/usr/src/linux-source-2.6.18# make prepare
debian:/usr/src/linux-source-2.6.18# make scripts
Complie the modules inside cpufreq
debian:/usr/src/linux-source-2.6.18# make M=./arch/i386/kernel/cpu/cpufreq
5 Apply complied speedstep module
debian:/usr/src/linux-source-2.6.18# cp arch/i386/kernel/cpu/cpufreq/speed*.ko /lib/modules/$(uname -r)/kernel/arch/i386/kernel/cpu/cpufreq
debian:/usr/src/linux-source-2.6.18# modprobe speedstep-centrino
6 Uncomment back or append the following line into /etc/modules uncomment back the speedstep-centrino
debian:/home/l# gedit /etc/modules
speedstep-centrino
cpufreq_conservative
cpufreq_ondemand
cpufreq_userspace
cpufreq_powersave
cpufreq_stats
save it and reboot.

Testing
See the voltage
debian:/home/l# cat /sys/devices/system/cpu/cpu0/cpufreq/voltage_table
972,876,796,748,716,700
Left most is the highest frequency scaled.This is compared to the available cpu scale.
See the available cpu scale.
debian:/home/l# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
1700000 1400000 1200000 1000000 800000 600000

Set the voltage
Voltage must follow the vid and vcc fomula vid =( vcc - 700)/16,
more detailed see HOWTO Undervolt a Pentium M CPU - Gentoo Linux Wiki
For example 0.972 is get from 17*16+700 = 972, 17 is vid.
debian:/home/l# echo 972,876,796,748,716,700 > /sys/devices/system/cpu/cpu0/cpufreq/voltage_table

Boot script.
Is time to install sysfsutils cpufrequtils
debian:/home/l#apt-get install sysfsutils cpufrequtils
Set ondemand profile.
debian:/home/l#gedit /etc/default/cpufrequtils
ENABLE="ture"
GOVERNOR="ondemand"
MAX_SPEED=1700000
MIN_SPEED=600000
Set permarnent boot script.
debian:/home/l# gedit /etc/sysfs.conf
Edit or append.
devices/system/cpu/cpu0/cpufreq/scaling_governor = ondemand
devices/system/cpu/cpu0/cpufreq/voltage_table = 972,876,796,748,716,700


references
https://www.dedigentoo.org/trac/linu...wto_ubuntu_001
CPU frequency scaling in Debian 4.0 Etch | ndap.net
HOWTO Undervolt a Pentium M CPU - Gentoo Linux Wiki

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