CONFIG WATCHDOG

Action

Configures the watchdog timer.

 

 

Syntax

CONFIG WATCHDOG = time

 

 

Remarks

Time

The interval constant in mS the watchdog timer will count to before it will reset your program.     Possible settings : 16 , 32, 64 , 128 , 256 , 512 , 1024 and 2048. Some newer chips : 4096, 8192.   The XMEGA has a 1 KHz clocked watchdog. For Xmega the following value in millisecond need to be used : 8 ,16,32,64,125,250,500,1000,2000,4000,8000 So 2000 will sets a timeout of 2 seconds.

 

Note that some new AVR's might have additional reset values such as 4096 and 8192.

 

When the WD is started, a reset will occur after the specified number of mS.

With 2048, a reset will occur after 2 seconds, so you need to reset the WD in your programs periodically with the RESET WATCHDOG statement.

 

Some AVR's might have the WD timer enabled by default. You can change this with the Fuse Bits.

 

After the CONFIG WATCHDOG statement, the watchdog timer is disabled. You can also use CONFIG WATCHDOG to change the time out value. This will stop the watchdog timer and load the new value.

After a CONFIG WATCHDOG, you always need to start the Watchdog with the START WATCHDOG statement.

 

Most new AVR chips have an MCUSR register that contains some flags. One of the flags is the WDRF bit. This bit is set when the chip was reset by a Watchdog overflow. The CONFIG WATCHDOG will clear this bit, providing that the register and bit is available in the micro.

When it is important to examine at startup if the micro was reset by a Watchdog overflow, you need to examine this MCUSR.WDRF flag before you use CONFIG WATCHDOG, since that will clear the flag.

 

For chips that have an enhanced WD timer, the WD timer is cleared as part of the chip initialize procedure. This because otherwise  the WD timer will only work once. If it is important that you know the cause of the reset, you can read the register R0 before you run other code.

 

When the chip resets, the status registers with the reset cause bits is saved into register R0.

This is done because the compiler need to reset these flags since otherwise they can not occur again. And before clearing the bits, the status is saved into register R0.

Using the GETREG() function, you can read the cause if there is a need to do so.

 

The sample below demonstrates how to store the WDRF bit if you need it, and print it later.

 

 

See also

START WATCHDOG , STOP WATCHDOG , RESET WATCHDOG

 

 

Example

'-----------------------------------------------------------------------------------------
'name : watchd.bas
'copyright : (c) 1995-2008, MCS Electronics
'purpose : demonstrates the watchdog timer
'micro : Mega88
'suited for demo : yes
'commercial addon needed : no
'-----------------------------------------------------------------------------------------
 
$regfile = "m88def.dat" ' specify the used micro
$crystal = 8000000 ' used crystal frequency
$baud = 19200 ' use baud rate
$hwstack = 32 ' default use 32 for the hardware stack
$swstack = 32 ' default use 32 for the SW stack
$framesize = 40 ' default use 40 for the frame space
Dim B As Byte
Dim Wdbit As Bit
Dim bWD As Byte
 
bWD=peek(0) ' read the wd flag
Print "Watchdog test" 
If bwd.wdrf = 1 Then ' there was a WD overflow
 Wdbit = 1 'store the flag
End If
 
Config Watchdog = 2048 'reset after 2048 mSec
If Wdbit = 1 Then 'just print it now since it is important that CONFIG WATCHDOG runs early as possible
 Print "Micro was reset by Watchdog overflow"
End If
 
Start Watchdog 'start the watchdog timer
Dim I As Word
For I = 1 To 1000
 Waitms 100
 Print I 'print value
 B = Inkey() ' get a key from the serial port
 If B = 65 Then 'letter A pressed
 Stop Watchdog ' test if the WD will stop
 Elseif B = 66 Then 'letter B pressed
 Config Watchdog = 4096 'reconfig to 4 sec
 Start Watchdog 'CONFIG WATCHDOG will disable the WD so start it
 Elseif B = 67 Then 'C pressed
 Config Watchdog = 8192 ' some have 8 sec timer
 'observe that the WD timer is OFF
 Elseif B = 68 Then 'D pressed
 Start Watchdog ' start it
 End If
 'Reset Watchdog
 'you will notice that the for next doesnt finish because of the reset
 'when you unmark the RESET WATCHDOG statement it will finish because the
 'wd-timer is reset before it reaches 2048 msec
 'When you press 'A' you will see that the WD will stop
 'When you press 'B' you will see that the WD will time out after 4 Sec
 'When you press 'C' you will see the WD will stop
 'When you press 'D' you will see the WD will start again timing out after 8 secs
Next
End
 
And this shows how to read the register r0:
Dim Breset As Byte
Breset = Peek(0)
When you show this value on an LCD display you will see a value of 7 the first time, and later a value of 15 when the WD reset occured.

Xmega Example

'----------------------------------------------------------------
' (c) 1995-2010, MCS
' xm128-WD.bas
' This sample demonstrates the Xmega128A1 Watchdog
'-----------------------------------------------------------------
 
$regfile = "xm128a1def.dat"
$crystal = 32000000
$hwstack = 64
$swstack = 64
$framesize = 64
 
'First Enable The Osc Of Your Choice
Config Osc = Enabled , 32mhzosc = Enabled
 
'configure the systemclock
Config Sysclock = 32mhz , Prescalea = 1 , Prescalebc = 1_1
 
Config Com1 = 19200 , Mode = Asynchroneous , Parity = None , Stopbits = 1 , Databits = 8
Config Input1 = Cr , Echo = Crlf ' CR is used for input, we echo back CR and LF
 
Open "COM1:" For Binary As #1
' ^^^^ change from COM1-COM8
 
Print #1 , "Xmega revision:" ; Mcu_revid ' make sure it is 7 or higher !!! lower revs have many flaws
 
Config Watchdog = 4000 'after 4 seconds a reset will occur if the watchdog is enabled
'possible value : 8 ,16,32,64,125,250,500,1000,2000,4000,8000
'these values are clock cycles, based on a 1 KHz clock !!!
 
Dim W As Word , B As Byte
Do
 W = W + 1
Print W
Waitms 500
 B = Inkey()
If B = "a" Then
 Start Watchdog
 Print "start"
Elseif B = "b" Then
 Stop Watchdog
 Print "stop"
Elseif B = "c" Then
 Config Watchdog = 8000
 Print "8 sec"
Elseif B = "d" Then
 Reset Watchdog
 Print "reset"
End If
Loop

Languages	English • Deutsch