[Desire Q&A, Help & Troubleshooting] oli.henning:
This thread should be a talk about the lowest possible voltage-levels which are well-known to be stable.

Background:

I'm using a Custom-ROM on my 'classic' Desire.

Nearly every Custom-ROM has a specialized Linux-kernel with "OCUV"-Feature.

(For those, who don't know what this means: OverClock/UnderVoltage ;))

With OC you can speed-up you Device.

Normally, the Desire has a maximum CPU-Clock of 998 MHz.

Most custom kernels offer an OC up to 1'113 MHz (+11%), some even go up to 1'190 Mhz (+19%).

The UV-Feature enables you to reduce the voltage of the CPU.

So you can save battery (longer stand-by)

or 'protect' your CPU from getting too hot while using CPU-intensive Apps or using Overclocking.

The HTC-Desire-CPU can work with these discrete CPU-clocks (MHz):

Official: 128,245,384,422,460,499,537,576,614,652,691,729,768,806,844,883,921,960,998

Overclocked: 1036,1075,1113 (or even more...)

The concrete CPU-Clock is chosen by a so called CPU-governor, according to the current requirements:

Normally, when the screen is turned of, then the CPU-clock is limited to 245 MHz. Even if your screen is on but you do nothing that looking on a steady-home-screen, your CPU-clock will be low. But when you do somthing (starting an App, playing a game...), then your CPU-clock wile rise (more or less quickly) up to the maximum-clock and will fall down again when your devices idles again.

Additionally there is a table which defines the conrete CPU-voltage-level for every single CPU-clock-speed. There are factory-default-values for this table (see table below). With the UV-Feature (Undervoltage) you can change this table, normally to lower voltage-levels (there is no need to increase the voltage).

But there are limits for UV: If the voltage for a specific CPU-clock drops under a CPU-model-specific value, then the CPU makes sudden calculation-errors and the software (your App or the whole Android-OS) get's unstable and crashes and you have to reboot yout phone.

Perhaps you even have to remove the battery because the device doesn't react on your Power-Button-Presses any more.

But: A (permanent) defect to your hardware is unlikely.

To start-over i present the result of some intensive tests i made with my device:

MHz Default(mV) Still-ok(mV) CRASH(mV)
128 975 825 800 (thx to rootSU)
245 1000 850 825
384 1025 850 825
422 1050 850 825
460 1050 875 (not yet tested)
499 1075 900 875
537 1075 925 (not yet tested)
576 1100 950 925
614 1100 950 (not yet tested)
652 1125 975 950
691 1150 1000 (not yet tested)
729 1175 1025 1000
768 1200 1025 (not yet tested)
806 1225 1050 1025
844 1250 1075 (not yet tested)
883 1275 1100 (not yet tested)
921 1275 1125 1100
960 1275 1150 (not yet tested)
998 1275 1175 1150
1036 1275 1200 (not yet tested)
1075 1275 1225 (not yet tested)
1113 1275 1225 1200

The voltages between my test-steps can easily be interpolated (for now).

To these 'min-but-still-ok-values' i added a 'stability-supplement' of 50mV and set up my device accordingly. I use the App "OC/UC Beater2" for this.

Now it's running for some days with no crashes. So far i can say: it's stable.

I would like to see other users to test these values and give a response here in this thread (dont's forget to add 50mV!!!!!).

Later (in a few days or weeks) i will suggest to reduce the table-values by 25mV and the cimmunity tests again.

Hope to get some responses. Thx.