24.6 Generated resets and interrupts
The watchdog generates a reset in the following events, also referred to as exceptions:
• A watchdog time-out
• Failure to unlock the watchdog within WCT time after system reset deassertion
• No update of the control and configuration registers within the WCT window after
unlocking. At least one of the following registers must be written to within the WCT
window to avoid reset:
• WDOG_ST_CTRL_H, WDOG_ST_CTRL_L
• WDOG_TO_VAL_H, WDOG_TO_VAL_L
• WDOG_WIN_H, WDOG_WIN_L
• WDOG_PRESCALER
• A value other than the unlock sequence or the refresh sequence is written to the
unlock and/or refresh registers, respectively.
• A gap of more than 20 bus cycles exists between the writes of two values of the
unlock sequence.
• A gap of more than 20 bus cycles exists between the writes of two values of the
refresh sequence.
The watchdog can also generate an interrupt. If IRQ_RST_EN is set, then on the above
mentioned events WDOG_ST_CTRL_L[INT_FLG] is set, generating an interrupt. A
watchdog reset is also generated WCT time later to ensure the watchdog is fault tolerant.
The interrupt can be cleared by writing 1 to INT_FLG.
The gap of WCT between interrupt and reset means that the WDOG time-out value must
be greater than WCT. Otherwise, if the interrupt was generated due to a time-out, a
second consecutive time-out will occur in that WCT gap. This will trigger the backup
reset generator to generate a reset to the system, prematurely ending the interrupt service
routine execution. Also, jobs such as counting the number of watchdog resets would not
be done.
24.7 Memory map and register definition
This section consists of the memory map and register descriptions.
Generated resets and interrupts
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Freescale Semiconductor, Inc.
