This is a spin-off of the endless overclocking thread http://talk.maemo.org/showthread.php?t=39753
The focus of this thread is not overclocking for improved performance but
how we save battery power with tricks like underclocking to 125MHz or reducing
the voltage for the different CPU frequencies.
A related thread is http://talk.maemo.org/showthread.php?t=43748

my latest low voltages kernels
http://wiki.maemo.org/Overclocking#I...mental_kernels

egoshin's advice http://talk.maemo.org/showpost.php?p...&postcount=189

smartreflex http://talk.maemo.org/showthread.php?t=48207
http://talk.maemo.org/showthread.php?t=49228
battery life http://talk.maemo.org/showthread.php?t=31020

powertop for N900 http://talk.maemo.org/showpost.php?p...3&postcount=21

Install battery-eye or batterygraph to monitor your battery consumption.
Please share your experiences with battery life here.

was using luhto's 900mhz for many days and did notice alot of heat when on load but was very stable.

trying the ulv of his 800mhz which is stable and not noticed much heat.

going to try your low volt one later today, can you tell me if you have tested 900mhz please?

titan: I now use the 2.6.28.10maemo-ulv-omap1

Do you use stock dsp in this kernels?

900MHz worked fine for me.
for 600-810 it uses the same lower DSP voltage as for 550.
for >=850 is uses the max. voltage with 500MHz.

i also would like to have best of both worlds.

So when i need power i have power (stable) at lets say 800-900 but when it can it should try to save as much power as possible, especially in idle or almost idle states.

So it would be nice to have a wiki that explains the best kernel for this and how to configure it correctly including things like those ondemand settings (up_threshold) and so on.

the instructions i would like to see is with a fiasco kernel, i installed now a few and that is the easiest way to install in my eyes (just one command....)
For me on device flashing is the preferred way because by default flasher35 doesnt even work for me (Win7x64) which is by the way quite annoying but it has been for a quite some time with nokia tools and the 64 bit world.. Even if that is currently the best selling OS.

i noticed HUGE battery consumption with ulv from lehto 1000mhz... 10 percent drain in 3 hours... idle with internet off... ill see how it goes for the rest of the day....

The MPU and DSP both use VDD1, so you don't really set DSP voltage. The values of vsel in the dsp table are ignored.

There's something wrong with your state of your phone at that time.
I'm using same ulv kernel at 1000Mhz. Lost about 3% after 4 hours of idle so far
With the non-ulv Lehto's 1Ghz kernel, I lost only about 5% after 8 hours of idle.

Currently running the ulv kernel @ 250/800
conky shows 810 speed and the dmesg | grep WARNING command returns no results.

I'm also trying the other mods mentioned in titan's opening post (egoshin advice, smartflex) and a bunch of other setting (lower screen brightness, turned off un-wanted notifications...etc)

I like the idea of this thread, I for one will be more happy with longer battery life if it meant I don't get to UBER-overclock, for exapmle only get to 700-750 but in exchange get an improved battery life but 25-30, no matter how fast the n900 can be, it's nothing more than an expensive brick once it runs out of juice

Titan

In your ULV kernel, it seems that after a call /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq is reset to 125000 from 124999 and after that the minimum frequency I can see in /sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_state is 250MHz instead of 125MHz

The only way to fix the issue is to do
echo 124999 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq

after every call