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NAME

       <avr/sleep.h>: Power Management and Sleep Modes -

   Functions
       void sleep_enable (void)
       void sleep_disable (void)
       void sleep_cpu (void)

Detailed Description

        #include <avr/sleep.h>

       Use of the SLEEP instruction can allow an application to reduce its
       power comsumption considerably. AVR devices can be put into different
       sleep modes. Refer to the datasheet for the details relating to the
       device you are using.

       There are several macros provided in this header file to actually put
       the device into sleep mode. The simplest way is to optionally set the
       desired sleep mode using set_sleep_mode() (it usually defaults to idle
       mode where the CPU is put on sleep but all peripheral clocks are still
       running), and then call sleep_mode(). This macro automatically sets the
       sleep enable bit, goes to sleep, and clears the sleep enable bit.

       Example:

           #include <avr/sleep.h>

           ...
             set_sleep_mode(<mode>);
             sleep_mode();

       Note that unless your purpose is to completely lock the CPU (until a
       hardware reset), interrupts need to be enabled before going to sleep.

       As the sleep_mode() macro might cause race conditions in some
       situations, the individual steps of manipulating the sleep enable (SE)
       bit, and actually issuing the SLEEP instruction, are provided in the
       macros sleep_enable(), sleep_disable(), and sleep_cpu(). This also
       allows for test-and-sleep scenarios that take care of not missing the
       interrupt that will awake the device from sleep.

       Example:

           #include <avr/interrupt.h>
           #include <avr/sleep.h>

           ...
             set_sleep_mode(<mode>);
             cli();
             if (some_condition)
             {
               sleep_enable();
               sei();
               sleep_cpu();
               sleep_disable();
             }
             sei();

       This sequence ensures an atomic test of some_condition with interrupts
       being disabled. If the condition is met, sleep mode will be prepared,
       and the SLEEP instruction will be scheduled immediately after an SEI
       instruction. As the intruction right after the SEI is guaranteed to be
       executed before an interrupt could trigger, it is sure the device will
       really be put to sleep.

       Some devices have the ability to disable the Brown Out Detector (BOD)
       before going to sleep. This will also reduce power while sleeping. If
       the specific AVR device has this ability then an additional macro is
       defined: sleep_bod_disable(). This macro generates inlined assembly
       code that will correctly implement the timed sequence for disabling the
       BOD before sleeping. However, there is a limited number of cycles after
       the BOD has been disabled that the device can be put into sleep mode,
       otherwise the BOD will not truly be disabled. Recommended practice is
       to disable the BOD (sleep_bod_disable()), set the interrupts (sei()),
       and then put the device to sleep (sleep_cpu()), like so:

           #include <avr/interrupt.h>
           #include <avr/sleep.h>

           ...
             set_sleep_mode(<mode>);
             cli();
             if (some_condition)
             {
               sleep_enable();
               sleep_bod_disable();
               sei();
               sleep_cpu();
               sleep_disable();
             }
             sei();

Function Documentation

   void sleep_cpu (void) Put the device into sleep mode. The SE bit must be
       set beforehand, and it is recommended to clear it afterwards.
   void sleep_disable (void) Clear the SE (sleep enable) bit.
   void sleep_enable (void) Put the device in sleep mode. How the device is
       brought out of sleep mode depends on the specific mode selected with
       the set_sleep_mode() function. See the data sheet for your device for
       more details.
       Set the SE (sleep enable) bit.

Author

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Version 1.6.8               <avr/sleep.h>: Power Management and Sleep Modes(3)