[Samsung Galaxy Nexus] szucsgf:
I'm going to do my best to explain what SmartReflex (SR) does and when you should and should not use it. I’m just going to address MPU voltages.

I will be using TricksterMod to adjust kernel settings. I am running AK Diamond Kernel v20. I'll give examples of specific frequencies and voltages available on this kernel. On other kennels different frequencies and voltages may apply but the theory remains the same.

SR is a power management technology developed by Texas Instruments. It dynamically undervolts to what it determines is the lowest stable voltage at each frequency. I've attached a chart which shows the available frequencies (on AK Diamond v20), their default voltages with SR off, and their voltages with SR on. The SR voltages might be slightly different on each device due to various software and hardware factors, but they generally won't differ by more than +/-10mV.

To find the SR voltages of your device: turn SR on, set Max CPU to 1350, set Min CPU to 180. Then swipe to the "Info" tab, scroll to the very bottom, wait for the frequency to settle at Min CPU, and read the MPU voltage at the bottom right. Repeat this for each frequency. Texas Instruments calls these the “Optimized” voltages.

The default SR Off voltages can be found under Trickster’s “Specific” tab under MPU Voltages. I’ll call these the “Default” voltages. These are adjustable by the user.

Here's how it works: With SR Off, the Default voltages are the only voltages your device will use for each frequency. When SR is on the Default voltages act as a maximum. Your device will not operate at a higher voltage for each frequency than what is specified here. If SR determines your device can operate at lower voltages it will lower the voltage. Once again, these Optimized voltages can be found under the “Info” tab.

Taking the 525Mhz frequency as an example: the Optimized voltage is 820mV, the Default voltage is 1003mV. With SR on, these voltages act as the minimum and maximum, respectively. If you keep SR on and lower the “Default” voltage, for example by -50 to 953mV, you will set a new cap for the maximum voltage. This likely won’t have any effect because your device is operating at 820mV anyway. However if you turn SR off, your device will operate at 953mV.

If you keep SR on but adjust voltage to below the Optimized voltage, your selected voltage will apply. Continuing the example of 525Mhz, if you keep SR on but lower the Default voltage to 800mV, your device will operate at 800mV instead of 820mV.

Q1: When should I keep SR on?

A1: The short answer is “always”. If you manually set a voltage above the Optimized voltage, SR will use the Optimized voltage. If you manually set a voltage lower than the Optimized voltage, your selected voltage will apply. With SR on you are always at the lower of the two voltages (SR on voltage = minimum of Optimized voltage and Default voltage).

Q2: When does it not matter?

A2: When you set a voltage lower than or equal to the Optimized voltage, your device will operate at your chosen voltage whether SR is on or off.

Q3: When should I turn SR off?

A3: The only time you need to turn SR off is if you are intentionally overvolting your device. One might do this to increase stability or for testing purposes.

Q4: "I undervolted by lowering all the Default voltages by (for example) -50mV and turned SR off. Is that OK?"

A4: Taking another look at the voltage chart attached, you'll notice that many Default voltages are more than (for example) 50mV above the Optimized voltages. So lowering all Default voltages by the same value across the board with SR off will result in some frequencies being undervolted and some frequencies being overvolted. This is likely not the desired result. Keeping SR on will prevent unintentional overvolting. In that case you will be undervolting some frequencies and the rest will operate at the Optimized voltages.

In short, unless you’re intentionally overvolting you can just keep SR on.

You might have noticed that with SR on several frequencies often use the same voltage. This allows for efficiently under- or over-clocking your device. I have a thread about this here:

http://xdaforums.com/showthread.php?t=2175147

Undervolting the Right Way: http://xdaforums.com/showthread.php?t=1558080

AK Kernel: http://xdaforums.com/showthread.php?t=1883298