[OLPC-devel] Thoughts on S3 resume.

[Chris Ball]

>> On Sun, 06 Aug 2006 01:12:53, Chris Ball <cjb at mrao.cam.ac.uk> said:

   > I'm having trouble getting into S3 on my A-test board, using the
   > devel image.  dmesg is attached; I'm seeing ACPI errors and
   > /proc/acpi/sleep doesn't exist, although the rest of /proc/acpi is
   > intact and functional.  I booted with acpi=force into kernel
   > 2.6.17-1.2396.fc6.

Sleep is working for me now, using /sys/power/state rather than
/proc/acpi/sleep.  So, to sleep on an A-test board, on devel image
42 or later after booting with acpi=force:

   date -d "2 minutes" +"%Y-%m-%d %H:%M:%S" > /proc/acpi/alarm
   echo -n "mem" > /sys/power/state

The resume will fall over if you're booted from USB, since the USB 
root disk is ejected/reinserted by the kernel, and has a new device
node after resume.  This is a pain.

I made some quick power measurements.  This is for the board and one 
USB flash drive, all other USB is being powered by a hub:

0s:    700mA # hit return, screen blanks, power constant at 700mA until..
20s:   100mA # light on board starts blinking.  What did we do for 20s?
2m:    700mA # light on board turns solid, but pressing keys does nothing
2m27s: 700mA # VGA returns, with ext3 errors and disk detection scrolling

These times would be more reliable if I were on serial rather than VGA,
so I'll get that going.  It does appear that we have at least 20 seconds
before the board hits S3 (on my board), though, and at least 20 from
when the board wakes up (power light solid, full power draw) to when 
the kernel resumes doing basic things like new device detection.

- Chris.
-- 
Chris Ball   <cjb at mrao.cam.ac.uk>    <http://blog.printf.net/>