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imp.deepsleepfor(sleepTime)

Puts the imp into deep sleep for the specified period

Availability

Device

Parameters

Name Type Description
sleepTime Integer The deep sleep duration in seconds (0—2419198)

Returns

Nothing

Description

This method causes the imp to enter a very low power mode (‘deep sleep’) and stop executing code for the specified period of time — or until the wake-up pin is triggered, if it has been activated. While the imp is in deep sleep, the current network interface is disabled.

Note This method is very similar in operation to server.sleepfor(). However, unlike server.sleepfor(), imp.deepsleepfor() does not perform a server.flush() operation to ensure that any pending messages are sent before sleep.

When the imp enters deep sleep, the execution of Squirrel code is stopped entirely. When the imp wakes up, its device code is loaded from its flash storage and restarted. No state data is preserved, with the exception of the special nv table, which will be maintained. The nv table is not preserved through a power-cycle.

In deep sleep, all of the imp’s pins are tri-stated, unless you have enabled your imp’s wake-up pin. The wake-up pin (and only the wake-up pin) has a weak pull-down.

The maximum sleep time is 2,419,198 seconds (28 days, minus two seconds).

Deep sleep mode draws approximately 6μA of current on the imp001 card, or 4μA on imp modules (the imp005 does not support deep sleep). The processor is effectively shut down. Upon waking from deep sleep, the device will be in a ‘warm boot’ state with code execution returning to the start of the script. Booting and reconnecting to the network will take a second or more, so this method may not be appropriate for very short sleep periods.

It is recommended practice to call imp.deepsleepfor() only when the imp is idle, ie. when impOS is ready for this to take place. This is best achieved by incorporating your imp.deepsleepfor() code inside a function that is registered to called when the imp goes idle. To do so, use the method imp.onidle():

imp.onidle(function(){
    imp.deepsleepfor(3600);
});

Note Using imp.wakeup() as an alternative to imp.onidle() is not recommended in this case, as any timeout provided can be no guarantee that the imp has become idle at that point. imp.onidle() is on the only way to be sure.

Module-specific Information

imp003

This method is not available on imp003-based devices with no 32kHz crystal and running impOS™ 34 and up.

imp004m

This method is not available on imp004m-based devices with no 32kHz crystal and running impOS 34 and up.

You will not be able to preserve data in the nv table during sleep: the imp004m does not implement nv table functionality. Please see the guide ‘Designing Hardware with the imp004m’ for workarounds.

imp005

imp005 devices are not currently capable of deep sleep, so imp.deepsleepfor() has been removed from the imp005. Using this call on an imp005 will cause an exception to the be thrown.

Example Code

This example wakes the imp up for about 0.05 seconds each minute to do some data logging. Once an hour it also fires up WiFi and dumps that hour’s readings to the server. Once DHCP and so on are taken into account, the hourly wake-up can last for several seconds. This technique enables the imp to use only tiny amounts of power overall which is useful when running from a battery.