wdt_samd21 Library

© 2022 Guglielmo Braguglia, updated on Jul 2022.

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A very simple library to activate, reset and deactivate the WDT on ATSAMD21.

Based on the work of MartinL (https://forum.arduino.cc/u/MartinL) on Arduino forum (Apr, 2018)

   • © 2022 Guglielmo Braguglia
   • © 2018 MartinL

The wdt_samd21 library allows, in a very easy way, on ATSAMD21 MCU, to activate, to periodically reset, to deactivate and to reactivate the WDT (Watch Dog Timer), which are the normal required functions for a simple use of the WDT for checking the correct execution of an application program.

Library usage and initialization

Customization

To define the "timeout" of the WDT you can use the constants defined in the SAMD21 core, in the wdt.h file:

WDT_CONFIG_PER_8        8 clock cycles ( 7.8 msec.)
WDT_CONFIG_PER_16      16 clock cycles (15.6 msec.)
WDT_CONFIG_PER_32      32 clock cycles (31.2 msec.)
WDT_CONFIG_PER_64      64 clock cycles (62.5 msec.)
WDT_CONFIG_PER_128    128 clock cycles ( 125 msec.)
WDT_CONFIG_PER_256    256 clock cycles ( 250 msec.)
WDT_CONFIG_PER_512    512 clock cycles ( 500 msec.)
WDT_CONFIG_PER_1K    1024 clock cycles ( 1 sec.)
WDT_CONFIG_PER_2K    2048 clock cycles ( 2 sec.)
WDT_CONFIG_PER_4K    4096 clock cycles ( 4 sec.)
WDT_CONFIG_PER_8K    8192 clock cycles ( 8 sec.)
WDT_CONFIG_PER_16K  16384 clock cycles (16 sec.)

... the defaul value, if nothing is passed to the initialization function, is WDT_CONFIG_PER_2K.

Initialization

To use this library first you have to add, at the beginning of your program:

#include <wdt_samd21.h>

... next you have to call the library functions.

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Library functions

wdt_init( unsigned long wdt_config_per )

Initialize the WDT with a timeout equal to the value passed as a parameter. It must be one of the values described in the "Customization" paragraph.

Example:

wdt_init ( WDT_CONFIG_PER_1K );

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wdt_reset( )

Must be called before the timeout time passes to reset the WDT counter. If you do not call it in time, the MCU reset.

Example:

wdt_reset ( );

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wdt_disable( )

Disable the WDT until it is reactivated again with a wdt_reEnable( ).

Example:

wdt_disable ( );

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wdt_reEnable( )

Re-enable the WDT disabled by a previous wdt_disable( ).

Example:

wdt_reEnable ( );

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Demo Program

The following example initializes the WDT for a timeout of 2 seconds, after which, in the loop(), it performs a for structure with a delay() of one second at each iteration, but sending a wdt_reset() command to the WDT to avoid the restart. At the end of the for structure, the wdt is first disabled then, after a 3 second delay(), is enabled again and, finally, a 4 second delay() is performed which causes the MCU to restart so, all that following the last delay(), is never executed.

#include <wdt_samd21.h>

void setup() {
   delay ( 500 );
   //
   Serial.begin ( 9600 );
   while ( !Serial ) {
      delay ( 100 );
   }
   //
   // Initialze WDT with a 2 sec. timeout
   wdt_init ( WDT_CONFIG_PER_2K );
}

void loop() {
   for ( byte i = 0; i < 5; i++ ) {
      // wait a second
      delay ( 1000 );
      // write on the serial port
      Serial.print ( "Iteration " );
      Serial.print ( i + 1 );
      Serial.println ( " of 5" );
      // "feed" the WDT to avoid restart
      wdt_reset();
   }
   //
   // now disable wdt and wait ...
   wdt_disable();
   Serial.println( "wdt disabled ..." );
   Serial.println ( "Now waiting for 3 seconds ..." );
   delay(3000);
   //
   // ... then reEnable the wdt ...
   wdt_reEnable();
   Serial.println( "wdt reEnabled ..." );
   //
   // ... and wait 4 seconds ... the WDT should restart the board
   Serial.println ( "Now waiting for 4 seconds ..." );
   delay ( 4000 );
   //
   Serial.println ( "*** You will never see this message printed ***" );
   delay ( 1000 );
}

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