Espressif ESP32 Technical Reference Manual page 522

19 Watchdog Timers (WDT)
• Reset a CPU core
When the stage expires the designated CPU core will be reset. MWDT0 CPU reset only resets the PRO
CPU. MWDT1 CPU reset only resets the APP CPU. The RWDT CPU reset can reset either of them, or both,
or none, depending on configuration.
• Reset the main system
When the stage expires, the main system, including the MWDTs, will be reset. In this article, the main
system includes the CPU and all peripherals. The RTC is an exception to this, and it will not be reset.
• Reset the main system and RTC
When the stage expires the main system and the RTC will both be reset. This action is only available in the
RWDT.
• Disabled
This stage will have no effects on the system.
When software feeds the watchdog timer, it returns to stage 0 and its expiry counter restarts from 0.
19.3.1.2 Write Protection
Both the MWDTs, as well as the RWDT, can be protected from accidental writing. To accomplish this, they have a
write-key register (TIMGn_WDTWPROTECT_REG
On reset, these registers are initialized to the value 0x50D83AA1. When the value in this register is changed
from 0x50D83AA1, write protection is enabled. Writes to any WDT register, including the feeding register (but
excluding the write-key register itself), are ignored. The recommended procedure for accessing a WDT is:
1. Disable the write protection
2. Make the required modification or feed the watchdog
3. Re-enable the write protection
19.3.1.3 Flash Boot Protection
During flash booting, the MWDT in timer group 0 (TIMG0), as well as the RWDT, are automatically enabled. Stage
0 for the enabled MWDT is automatically configured to reset the system upon expiry; stage 0 for the RWDT resets
the RTC when it expires. After booting, the register TIMERS_WDT_FLASHBOOT_MOD_EN should be cleared to
stop the flash boot protection procedure for the MWDT, and RTC_CNTL_WDT_FLASHBOOT_MOD_EN should be
cleared to do the same for the RWDT. After this, the MWDT and RWDT can be configured by software.
19.3.1.4 Registers
The MWDT registers are part of the timer submodule and are described in the
RWDT registers are part of the RTC submodule and are described in the
Espressif Systems
for the MWDT, RTC_CNTL_WDTWPROTECT_REG
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for the RWDT.)
Timer Registers
RTC Registers section.
ESP32 TRM (Version 5.2)
section. The