(mention /dev/rtc ioctl for scheduled resume from suspend)
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Latest revision as of 18:00, 12 March 2010
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The alarm daemon provides an interface for applications to register times at which an application needs to do a specific task.
 Usage Cases
- An alarm should turn on the phone if needed
- I want to specify relative and absolute times (i.e. in 5 hours, on May 1st 2007, 2:00pm)
 Architectural Details
The alarm daemon will probably be part of neod since it will need to set the RTC alarm for the next event. The interface for the applications is exposed via dbus.
 Implementation Recommendations
At start neod will have to query the next event in eds (to determine when the next wakeup has to occur). If a new event is added eds will broadcast the change through dbus.
Applications will (de-)register for a specific time at which the alarm daemon (neod) will call the application with a special command line parameter to reflect that the application has been called for an alarm.
 Unresolved Issues
- If the device is powering down during the alarm we might miss the RTC alarm. Maybe we should just move the alarm time back a minute if we are powering down and the alarm is near?
- What do we do if the application is already running?
 Time sources
An alarm daemon can not operate without accurate time. We have a number of possible time sources:
- view: sudo hwclock
- set from system time: sudo hwclock --systohc
- note that ioctl to /dev/rtc can be used to configure wakeup from suspend at a given time (see e.g. fso-frameworkd source code on how this can be done).
- view: echo d | netcat -w1 localhost gpsd
 GSM operator time
- It is not known how this can be accessed
 Other sources
- If you never suspend your phone then the system time could be used but this is not very practical.
- Does the GSM chip have its own clock (it is a full-blown ARM afterall)?
 Questions and Answers