NAME

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

SYNOPSIS

   Functions
       void sleep_enable (void)
       void sleep_disable (void)
       void sleep_cpu (void)
       void sleep_mode (void)
       void sleep_bod_disable (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_bod_disable (void) [extern]
       Disable BOD before going to sleep. Not available on all devices.

   void sleep_cpu (void) [extern]
       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) [extern]
       Clear the SE (sleep enable) bit.

   void sleep_enable (void) [extern]
       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.

   void sleep_mode (void) [extern]
       Put the device into sleep mode, taking care of setting the SE bit before, and clearing it afterwards.

Author

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