Thread: PRS-T1 Enormous battery drain
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Old 07-22-2012, 11:31 AM   #3
RhialtoFalu
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Posts: 21
Karma: 548
Join Date: Oct 2011
Location: The Netherlands
Device: PRS-T1
uboot: thanks for that lead. I have been poking at my T1 for the last week or so, and it seems that the problem has resolved "itself". Or at least, I have some idea of what might have fixed it but I'm not 100% sure about that. (I am still in the dark about how the problem started in the first place).

Here is the narrative (for the benefit of people having similar problems who might now find this through google):

I poked around with BetterBatteryStats (BBS), both while the reader was connected to USB (and charging), and when disconnected. However BBS had a tendency to stop responding as soon as I disconnected the USB cable, so that wasn't terribly useful. Also it managed to write a log file only twice out of many many attempts.

BBS showed active kernel wake locks for pretty much most of the time: past_wake_lock for over 90%... that's what apparently kept the reader awake. As already shown above, there was also a "pastlog_thread" being relatively active. "past_wake_lock" was not known by google!

Only after several days I thought to look at the linux system log (through the dmesg command). It turned out to contain only lines like this:
Code:
<3>[PASTLOG Err:past_search_reader(459)]Payload size error : offset=5213917 2776
It doesn't show any date stamps so you can't see how often these messages are logged, but I'm guessing there would be one at least every few seconds - maybe even many messages per second.

Searching for a file named pastlog, I found that it is a command, and a device:

Code:
./system/bin:
-rwxr-xr-x root     shell        9824 2011-12-21 07:01 pastlog

./sys/devices/virtual/misc/pastlog:
-rw-r--r-- root     root         4096 2012-07-20 19:43 uevent
-r--r--r-- root     root         4096 2012-07-22 11:52 dev
lrwxrwxrwx root     root              2012-07-22 11:52 subsystem -> ../../../../class/misc
drwxr-xr-x root     root              2012-07-20 19:43 power

./sys/devices/virtual/misc/pastlog/power:
-rw-r--r-- root     root         4096 2012-07-22 11:52 control
-rw-r--r-- root     root         4096 2012-07-22 11:52 wakeup

./sys/dev/char:
lrwxrwxrwx root     root              2012-07-22 11:52 10:46 -> ../../devices/virtual/misc/pastlog

./sys/module:
drwxr-xr-x root     root              2012-07-22 11:52 pastlog

./sys/module/pastlog:
drwxr-xr-x root     root              2012-07-22 11:52 parameters

./sys/module/pastlog/parameters:
-r--r--r-- root     root         4096 2012-07-22 11:52 pastlog_h
-r--r--r-- root     root         4096 2012-07-22 11:52 pastlog_emmc
-r--r--r-- root     root         4096 2012-07-22 11:52 pastlog_state

./dev:
crw-rw-rw- root     root      10,  46 2012-07-20 19:43 pastlog
I tried the "pastlog" command, and was presented with a long log output from Android (apparently this is an Android-level log file, like the syslog is the Linux-level log).

I suspect that this caused the following 2 lines in the syslog and ended the problem:

Code:
<3>[PASTLOG Err:past_read_cache(218)]read error : pos=3177588 size=4096 offset=3176960
<4>[PASTLOG Info:past_search_reader(464)]cannot read -> log buffer reset

Last edited by RhialtoFalu; 07-22-2012 at 11:43 AM.
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