Deep sleep in glowlight 4/4e and modern nooks

[Tialex]

Hi,

jumping from NST to "glowlight 4" (4e actually) I was disappointed at how little a single charge were allowing to read. Direct tests revealed something like 8 hours of reading from 90% to 10%. This was mostly with third-party readers. Then, I installed BetterBatteryStats (BBS) and made some observations, hoping that as I expected, the system would fall into Deep Sleep from time to time outside of the locked state.

It was to no avail except when I noticed that the BN reader app did fall into DS between page turns. Since then I never noticed any other app to activate DS. Actually the deep sleep behavior of BN app was also non-constant. The primary observation is when I made different tests when the delay between turns were different and I calculated the time spent in the full wake state, there was a constant wake time about 6-10 seconds that could never be decreased. But for 30 seconds page turns it was already ok for saving the battery life.

I have plans to investigate whether an app can force the system to fall into DS without going into the lock mode or changing the screen contents, but I would like to be sure the things I noticed are the same for all devices in the wild and it's not specific to my particular instance. If somebody from the community may find time and take some tests, that would be very useful. I will explain how I did mine, but I'm sure there are other apps and other means to achieve the same.

So, the questions are:

1. Can someone detect deep sleeping outside the locked state
2. Is the BN app the only one that effectively utilizes it?
3. Is it the same for all nooks after NST. I'm excluding it because NST probably had another system for DS trickery, because I could use any third-party apps for weeks. So the third question probably is what models are affected

So my testing steps :

• My device is not rooted (yet) so the following tests are possible with any device with adb access.
• To avoid background processes involving in the tests, I changed three settings is the Developer Options. "Don't keep activities" was switched on. This effectively stops any activity that the user leaves. "Background process limit" was set to one. I'm not sure whether this is important or not. "Background check" lists several services from the installed applications. I disabled all except the Android keyboard.
• Installed BetterBatteryStats (BBS). The community version is available at XDA The app interprets the power statistics that virtually any android device are collecting. In order to work one should have either rood access or to give it three permissions listed in the forum thread (using adb). There are proabably other apps effectively doing the same (Wakelock detector comes to mind), but I'm not familiar with them
• The app is not so scary after all. Basically it shows different states of the devices and their corresponding time and percentage. When we know the usage style like how much was spent with the screen on, with heavy apps performing something or in the locked state, the numbers should correspond or point out to the reason why they are different to what is expected.
• The program is flexible in what the starting point for observation is. We're mostly interesting in using Custom feature. When you go to the menu and tap "Set Custom ref." then the app for the Custom kind (in the drop in listbox containing also Unplugged, Boot) would show the numbers for the period from the moment you clicked to the moment you returned to the app. For instance, for the scenario "investigate a reader app for half an hour" we should set the Custom reference, return to the reader app, after half and hour return to the BBS and look at the "Custom" set of value in order to see whether something important took place (and time) or not.
• What we are interested mostly in BBS whether the Summary contains the item Deep Sleep and what percentage it shows. If you lock the device and unlock it after some time, you will see this item because the DS in the locked state is a norm. This is when almost all on-board devices are turning into a low-energy mode (and CPU also) until some approved interruption (like buttons click or screen tap) wake it up. But we would like to find it when the nook is not in the locked state. This is important point about eInk devices. Since they don't need energy to keep the screen image, any eInk device might go into DS while still "pretending" like it continues to work, this is what takes place between the page turns when you use BN reader app (the general smartphone with LCD screen should switch the screen completely in order to preserve energy with such efficiency). The funny things is that early eInk readers sometimes listed not the time for a single charge, but the number of page turns due to this specifics.
• The other interesting item is Waklocks-PowerManagerService.Display. Its percentage should be around (100% minus DS percentage) and the counter should probably correspond to the number of times page were turned.

Any results are appreciated. Thanks.

[pazos]

Originally Posted by Tialex

Is the BN app the only one that effectively utilizes it?

Most likely yes. The Nook reader app at least. Probably the other stock apps if there's any.

It also might be possible to do it on 3rd party apps but it is not part of android, so it requires a developer with a device that does RE the binaries to know which function call trips the DS.

There's a chance that the specific code path is restricted to system apps, so nobody can tell you without doing the work first.

Originally Posted by Tialex

What models are affected?

Good question. I bet the old ones where you didn't had the chance to run 3rd party apps were not affected, but I'm not really sure. My answer is based on

1. They were Freescale/iMX boards with a good idle power draw
2. Running very old versions of android where Doze isn't available.

[Tialex]

Originally Posted by pazos

There's a chance that the specific code path is restricted to system apps, so nobody can tell you without doing the work first.

Thanks for your thoughts. The links to the doze docs you mentioned helped to research whether the commands to enforce DS might be used by an app. Unfortunately it don't look very promising.

Also it just happened that I rooted my 4e and grab the logcat after a dozen of page flips in the BN app (bn.ereader). Looks like they use some proprietary lib epdUtils (probably vaguely googlable in the context of Sony eInk readers, epd probably stands for Electronic Paper Display) and the method (or call) setDirectSuspend. When the line with true

....EpdUtils: setDirectSuspend: true

then 2.5 seconds pass until the system goes to deep sleep and the logcat stops reporting anything at all until (in my case) hardware button KEYCODE_F11 is pressed, after that about 3.5 seconds passes until the corresponding call is noticed

... EpdUtils: setDirectSuspend: false

The 6-7 unavoidable seconds I previosly mentioned is this 2.5 + 3.5 seconds between these calls. Now I really doubt anyone can find a non-B&N app performing the same wizardly...

[Tialex]

Originally Posted by pazos

Most likely yes. The Nook reader app at least. Probably the other stock apps if there's any.

It also might be possible to do it on 3rd party apps but it is not part of android, so it requires a developer with a device that does RE the binaries to know which function call trips the DS.

There's a chance that the specific code path is restricted to system apps, so nobody can tell you without doing the work first.

The setting in question is probably found (power_enhance_enable), and it is also possible that other android/eInk devices like MobiScribe Wave might also use it. Disclaimer: the user on XDA is me, I decided to cross-link it from here because maybe there are still some users here interested. Besides, I still don't know how to utilize this knowledge effectively. Any hints are appreciated.