1.. zephyr:code-sample:: esp32-xt-wdt
2   :name: XTAL32K Watchdog Timer (WDT)
3
4   Trigger watchdog interrupt on external 32K crystal failure.
5
6Overview
7********
8
9This sample shows how to work with XTAL32K Watchdog Timer (XT WDT) peripheral.
10To properly run this sample, you need to have a board with an external 32.728 Hz
11crystal oscillator connected to the XTAL_32K_P and XTAL_32K_N pins.
12
13The app will ask for the crystal removal to simulate a crystal failure and trigger
14the XT WDT interrupt. Internally the hardware switch the RTC SLOW clock source from
15ESP32_RTC_SLOW_CLK_SRC_XTAL32K to ESP32_RTC_SLOW_CLK_SRC_RC_SLOW (136 KHz for C3 and S3 /
169 KHz for S2).
17
18Supported SoCs
19**************
20
21The following SoCs supports the XT WDT peripheral:
22
23* ESP32-C3
24* ESP32-S2
25* ESP32-S3
26
27Building and Running
28********************
29
30Make sure you have your board connected over USB port and the external crystal is connected
31to pins XTAL_32K_P and XTAL_32K_N.
32
33.. code-block:: console
34
35   west build -p -b esp32s3_devkitm/esp32s3/procpu samples/boards/espressif/xt_wdt
36   west flash
37
38If using another supported Espressif board, replace the argument in the above
39command with a proper board name (e.g., ``esp32s2_saola``).
40
41Sample Output
42=============
43
44To check output of this sample, run ``west espressif monitor`` or any other serial
45console program (e.g., minicom, putty, screen, etc).
46This example uses ``west espressif monitor``, which automatically detects the serial
47port at ``/dev/ttyUSB0``:
48
49.. code-block:: console
50
51   $ west espressif monitor
52
53.. code-block:: console
54
55   *** Booting Zephyr OS build v3.6.0-3896-gb4a7f061524f ***
56   [00:00:01.287,000] <inf> xt_wdt_sample: XT WDT Sample on esp32s3_devkitm/esp32s3/procpu
57   [00:00:01.287,000] <inf> xt_wdt_sample: Current RTC SLOW clock rate: 32768 Hz
58   [00:00:01.287,000] <inf> xt_wdt_sample: Remove the external 32K crystal to trigger the watchdog
59   XT WDT callback
60   [00:00:03.554,000] <inf> xt_wdt_sample: Current RTC SLOW clock rate: 136000 Hz
61