Originally Posted by MedLine
thanks for new kernel, 061811 OC kernel problem-free nearly 2 weeks, time to move on.
trying to undervolt cm7 on 063011 but think my nook not cooperating. at stock voltage my sr_adjust_vsel (pastebin here
) somewhat resembles what searius posted few days ago
, with opp1 - 3 already undervolted although not as generously as searius. if i use Nook Tweaks to reduce opp1 - 3 by 100mV each i think my nook just adjusts the voltage right back to nearly where it was, if i'm reading the sr_adjust_vsel numbers correctly (pastebin here
), regardless of any concurrent underclocking.
other than that it's probably going to be problem free with 063011 kernel, like it's been for a long time now.
Well, I am not overriding SmartReflex. I believe this process also warrants explanation:
SmartReflex is TI's version of dynamic voltage control. Every Nook has values in read-only registers that seeds the voltage calibration algorithms. These algorithms will choose a voltage per stepping based upon your specific hardware. In essense, the voltage assigned in the kernel is a sort of suggestion. SmartReflex will then take that suggestion along with the values in the read-only registers and decided on a voltage that is stable. In other words, when you assign a voltage for a stepping, SmartReflex will decide on a voltage based upon your input. SmartReflex has a limited window around your suggested voltage to choose from, for example it might be +/- 0.5v from what you choose in Nook Color Tweaks.
SmartReflex has two main purposes:
- By calibrating the voltage based on your hardware, the Nook can change the voltage as your CPU ages. Resistance often increases with age and may require additional voltage to remain stable, say 5 years from now.
- SmartReflex also aims to use the least voltage possible. Your Nook may need less voltage than mine does to remain stable at 800mhz.
So, SmartReflex actually undervolts already, as I've said in the past. However, SmartReflex is often fairly conservative with undervolting, especially on the upper steppings like 3, 4 and 5.
This means undervolting on stepping 1 or 2 may not have much, if any impact, on the final voltage the Nook decides to run. In my experience, stepping 1 and 2 are already well undervolted already and decreasing the voltage only leads to a 0.03v change. This may or may not be true for your Nook though as each can run at different voltages.
I think voltage control has the most value in the 4th and 5th stepping. Perhaps you only want to overclock to 1.1ghz. In this case, I would make stepping 5 1.1ghz and then decrease the voltage on stepping 5. Here, the voltage control can make a significant impact. The same can be true if you want to increase the voltage on stepping 4 or 5.
Also note that I reset the calibrated voltage after you change the voltage in Nook Color Tweaks. If you inspect sr_adjust_vsel you will see that the right hand columns will be 0x0. The calibration will not take place until your Nook changes steppings. Once the Nook goes to the stepping with 0x0 you will see it populate with the calibrated voltage.