Espressif ESP32 Technical Reference Manual page 521

19 Watchdog Timers (WDT)
19 Watchdog Timers (WDT)
19.1 Introduction
The ESP32 has three watchdog timers: one in each of the two timer modules (called Main System Watchdog
Timer, or MWDT) and one in the RTC module (which is called the RTC Watchdog Timer, or RWDT). These
watchdog timers are intended to recover from an unforeseen fault, causing the application program to abandon
its normal sequence. A watchdog timer has four stages. Each stage may take one out of three or four actions
upon the expiry of a programmed period of time for this stage, unless the watchdog is fed or disabled. The
actions are: interrupt, CPU reset, core reset and system reset. Only the RWDT can trigger the system reset, and
is able to reset the entire chip and the main system including the RTC itself. A timeout value can be set for each
stage individually.
During flash boot, the RWDT and the first MWDT start automatically in order to detect and recover from booting
problems.
19.2 Features
• Four stages, each of which can be configured or disabled separately
• Programmable time period for each stage
• One out of three or four possible actions (interrupt, CPU reset, core reset and system reset) upon the
expiry of each stage
• 32-bit expiry counter
• Write protection, to prevent the RWDT and MWDT configuration from being inadvertently altered.
• Flash boot protection
If the boot process from an SPI flash does not complete within a predetermined period of time, the watch-
dog will reboot the entire main system.
19.3 Functional Description
19.3.1 Clock
The RWDT is clocked from the RTC slow clock RTC_SLOW_CLK. The MWDT clock source is derived from the
APB clock APB_CLK via a pre-MWDT 16-bit configurable prescaler. For either watchdog, the clock source
is fed into the 32-bit expiry counter. When this counter reaches the timeout value of the current stage, the
action configured for the stage will execute, the expiry counter will be reset and the next stage will become
active.
19.3.1.1 Operating Procedure
When a watchdog timer is enabled, it will proceed in loops from stage 0 to stage 3, then back to stage 0 and
start again. The expiry action and time period for each stage can be configured individually.
Every stage can be configured for one of the following actions when the expiry timer reaches the stage's timeout
value:
• Trigger an interrupt
When the stage expires an interrupt is triggered.
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