Technical Q&A HW04

PowerBook and Sleep Mode

Q: Our multimedia presentation software does not awaken properly on a PowerBook that has come out of sleep mode. Are there any special handling requirements to recover from sleep mode? What event should we be watching for?

A: These are some of the changes to the system state when a PowerBook goes to sleep:

• All AppleTalk connections are lost, as the AppleTalk driver is turned off.

• The serial ports are entirely shut down to conserve power.

It is not clear why these two changes would affect your multimedia presentation software. However, there are two Macintosh Technotes available that relate to your situation: "HW 24, Little PowerBook in Slumberland," which provides a brief overview of the sleep process, and "HW 31, Sleep Queue Tasks," which presents additional material regarding the sleep process. The second Technote includes sample code that demonstrates a sleep-queue task implementation. The sleep-queue task provides a means by which your program can save state information that otherwise might be lost. Typically, this is important for a networked process, but it's not clear why your application would have to monitor this type of information.

You might want to implement a sleep-queue handler so you can drop to the debugger when the handler is notified that the unit is waking up. This would allow you to take debugging steps before a crash occurs.