NAME

       avr_watchdog - <avr/wdt.h>: Watchdog timer handling

SYNOPSIS

   Macros
       #define wdt_reset()   __asm__ __volatile__ ('wdr')
       #define WDTO_15MS   0
       #define WDTO_30MS   1
       #define WDTO_60MS   2
       #define WDTO_120MS   3
       #define WDTO_250MS   4
       #define WDTO_500MS   5
       #define WDTO_1S   6
       #define WDTO_2S   7
       #define WDTO_4S   8
       #define WDTO_8S   9

   Functions
       static __inline__ __attribute__ ((__always_inline__)) void wdt_enable(const uint8_t value)

Detailed Description

       #include <avr/wdt.h>

       This header file declares the interface to some inline macros handling the watchdog timer present in many
       AVR devices. In order to prevent the watchdog timer configuration from being accidentally altered by a
       crashing application, a special timed sequence is required in order to change it. The macros within this
       header file handle the required sequence automatically before changing any value. Interrupts will be
       disabled during the manipulation.

       Note
           Depending on the fuse configuration of the particular device, further restrictions might apply, in
           particular it might be disallowed to turn off the watchdog timer.

       Note that for newer devices (ATmega88 and newer, effectively any AVR that has the option to also generate
       interrupts), the watchdog timer remains active even after a system reset (except a power-on condition),
       using the fastest prescaler value (approximately 15 ms). It is therefore required to turn off the
       watchdog early during program startup, the datasheet recommends a sequence like the following:

       #include <stdint.h>
       #include <avr/wdt.h>

       uint8_t mcusr_mirror __attribute__ ((section (".noinit")));

       void get_mcusr(void) \
         __attribute__((naked)) \
         __attribute__((section(".init3")));
       void get_mcusr(void)
       {
         mcusr_mirror = MCUSR;
         MCUSR = 0;
         wdt_disable();
       }

       Saving the value of MCUSR in mcusr_mirror is only needed if the application later wants to examine the
       reset source, but in particular, clearing the watchdog reset flag before disabling the watchdog is
       required, according to the datasheet.

Macro Definition Documentation

   #define wdt_reset()   __asm__ __volatile__ ('wdr')
       Reset the watchdog timer. When the watchdog timer is enabled, a call to this instruction is required
       before the timer expires, otherwise a watchdog-initiated device reset will occur.

   #define WDTO_120MS   3
       See WDTO_15MS

   #define WDTO_15MS   0
       Symbolic constants for the watchdog timeout. Since the watchdog timer is based on a free-running RC
       oscillator, the times are approximate only and apply to a supply voltage of 5 V. At lower supply
       voltages, the times will increase. For older devices, the times will be as large as three times when
       operating at Vcc = 3 V, while the newer devices (e. g. ATmega128, ATmega8) only experience a negligible
       change.

       Possible timeout values are: 15 ms, 30 ms, 60 ms, 120 ms, 250 ms, 500 ms, 1 s, 2 s. (Some devices also
       allow for 4 s and 8 s.) Symbolic constants are formed by the prefix WDTO_, followed by the time.

       Example that would select a watchdog timer expiry of approximately 500 ms:

       wdt_enable(WDTO_500MS);

   #define WDTO_1S   6
       See WDTO_15MS

   #define WDTO_250MS   4
       See WDTO_15MS

   #define WDTO_2S   7
       See WDTO_15MS

   #define WDTO_30MS   1
       See WDTO_15MS

   #define WDTO_4S   8
       See WDTO_15MS Note: This is only available on the ATtiny2313, ATtiny24, ATtiny44, ATtiny84, ATtiny84A,
       ATtiny25, ATtiny45, ATtiny85, ATtiny261, ATtiny461, ATtiny861, ATmega48, ATmega88, ATmega168, ATmega48P,
       ATmega88P, ATmega168P, ATmega328P, ATmega164P, ATmega324P, ATmega644P, ATmega644, ATmega640, ATmega1280,
       ATmega1281, ATmega2560, ATmega2561, ATmega8HVA, ATmega16HVA, ATmega32HVB, ATmega406, ATmega1284P,
       AT90PWM1, AT90PWM2, AT90PWM2B, AT90PWM3, AT90PWM3B, AT90PWM216, AT90PWM316, AT90PWM81, AT90PWM161,
       AT90USB82, AT90USB162, AT90USB646, AT90USB647, AT90USB1286, AT90USB1287, ATtiny48, ATtiny88.

       Note: This value does not match the bit pattern of the respective control register. It is solely meant to
       be used together with wdt_enable().

   #define WDTO_500MS   5
       See WDTO_15MS

   #define WDTO_60MS   2
       See WDTO_15MS

   #define WDTO_8S   9
       See WDTO_15MS Note: This is only available on the ATtiny2313, ATtiny24, ATtiny44, ATtiny84, ATtiny84A,
       ATtiny25, ATtiny45, ATtiny85, ATtiny261, ATtiny461, ATtiny861, ATmega48, ATmega48A, ATmega48PA, ATmega88,
       ATmega168, ATmega48P, ATmega88P, ATmega168P, ATmega328P, ATmega164P, ATmega324P, ATmega644P, ATmega644,
       ATmega640, ATmega1280, ATmega1281, ATmega2560, ATmega2561, ATmega8HVA, ATmega16HVA, ATmega32HVB,
       ATmega406, ATmega1284P, ATmega2564RFR2, ATmega256RFR2, ATmega1284RFR2, ATmega128RFR2, ATmega644RFR2,
       ATmega64RFR2 AT90PWM1, AT90PWM2, AT90PWM2B, AT90PWM3, AT90PWM3B, AT90PWM216, AT90PWM316, AT90PWM81,
       AT90PWM161, AT90USB82, AT90USB162, AT90USB646, AT90USB647, AT90USB1286, AT90USB1287, ATtiny48, ATtiny88,
       ATxmega16a4u, ATxmega32a4u, ATxmega16c4, ATxmega32c4, ATxmega128c3, ATxmega192c3, ATxmega256c3.

       Note: This value does not match the bit pattern of the respective control register. It is solely meant to
       be used together with wdt_enable().

Function Documentation

   static __inline__ __attribute__ ((__always_inline__)) const [static]
       Enable the watchdog timer, configuring it for expiry after timeout (which is a combination of the WDP0
       through WDP2 bits to write into the WDTCR register; For those devices that have a WDTCSR register, it
       uses the combination of the WDP0 through WDP3 bits).

       See also the symbolic constants WDTO_15MS et al.

Author

       Generated automatically by Doxygen for avr-libc from the source code.