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imp.deepsleepfor(sleepTime)

Disconnects the imp from WiFi and puts it into deep sleep for the specified period

Availability

Device

Returns

Nothing

Parameters

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

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, WiFi is disabled.

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 pin 1 (imp001, imp002) or pin W (imp003) as the 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 the imp002 and imp003 modules. 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 WiFi 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 any data that your device needs to send to the server has been sent. 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() in this case as an alternative to imp.onidle() is not recommended, 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.

imp.deepsleepfor() is closely related to server.sleepfor() except that imp.deepsleepfor() does not perform a server.flush operation before sleep and any pending messages may not be sent.

Module-specific Notes

imp003

This method is not available on imp003-based devices with no 32kHz crystal and running impOS™ release 34 and up. Customers using this call to cause a device reset will now find that its use invokes a Squirrel runtime error instead. The method’s presence can be used to indicate whether or not a crystal has been detected:

if ("deepsleepfor" in imp) {
  ...
}

imp004m

If you make use of deep sleep for an imp004m-based product, you will not be able to preserve data in the nv table during sleep. This is because the imp004m does not implement nv table functionality. Please see the preliminary guide ‘Designing Hardware with the imp004m’ for possible workarounds.

imp005

imp005 devices are not currently capable of deep sleep, so imp.deepsleepfor() has been removed from the imp005. Customers using this call to cause a device reset will now find that its use causes a Squirrel runtime error instead.

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.