1. How to get available wakeup source?
- cat /sys/kernel/debug/wakeup_sources
2. How to enable the wakeup source?
- find /sys/devices/ -iname wakeup
- 'echo enabled > /sys/device/.../power/wakeup' to enable the wakeup source
3. How not to suspend the serial console when put system to suspend by ' echo mem > /sys/power/state'?
- after boot, echo N > /sys/module/printk/parameters/console_suspend
- OR modify kernel booting param, and add no_console_suspend.
4. How to suspend system to RAM?
- echo mem > /sys/power/state
5. How to resume system after suspend?
- depend on what wakeup source is available and enabled
- if rtc wakeup is OK, you can use 'rtcwake -m mem -s 10' to suspend the system 10 seconds to RAM, after the time expires, it rtc resume system.
- if uart is OK, you can 'echo mem > /sys/power/state', then any activity in serial console will wakeup system.
