avr_watchdog(3)

💖 NAME 💖

avr_watchdog — literally that's it, that's the name, no notes 🎀

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🌸 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)

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🦋 DETAILED DESCRIPTION 🦋

#include <avr/wdt.h>

okay so bestie, this header file declares the interface to some inline macros that handle the watchdog timer living inside a whole bunch of AVR devices 🐶⏰

and here's the ✨drama✨ — because nobody wants a crashing app to just casually wander in and mess with the watchdog timer config, changing it requires a special timed sequence. the macros in this header file handle that whole required sequence automatically before they change any value, so you don't have to sweat it. also, interrupts will be disabled during the manipulation. periodt 💅

Note: depending on the fuse configuration of your particular device, further restrictions might apply — in particular, it might be disallowed to turn off the watchdog timer. so like, know your fuses, fr fr 😭

Now, a big one. For newer devices (ATmega88 and newer, effectively any AVR that has the option to also generate interrupts), the watchdog timer stays active even after a system reset — except a power-on condition — and it's running the fastest prescaler value (approximately 15 ms). so you are required to turn off the watchdog early during program startup, and 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. no cap 🔥

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🎀 MACRO DEFINITION DOCUMENTATION 🎀

#define wdt_reset() __asm__ __volatile__ ('wdr')

Reset the watchdog timer. When the watchdog timer is enabled, you have to call this instruction before the timer expires — otherwise, a watchdog-initiated device reset will occur 💀 like, the timer will eat your program. reset it. do it. 🫶

#define WDTO_120MS 3

See WDTO_15MS 👀

#define WDTO_15MS 0

Symbolic constants for the watchdog timeout 💫 and because 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(). so like, don't go treating it as a register value bestie 🙈

#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(). same warning, same energy, don't skip it 💅

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🌈 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. 👑

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👑 AUTHOR 👑

Generated automatically by Doxygen for avr-libc from the source code. she was born from the source, your honor 🧚

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and that's the whole page bestie 🫶 this was Version 2.1.0, dated Sat Jan 29 2022, and it lives under the name avr_watchdog(3) 💖 go reset your watchdog before it resets you 💅✨