External RTC 32768Hz crystal

[chriselef]

Hello all,

The module is an ESP32-WROOM-32 (ESP32D0WDQ6 (revision 1))
On a new product we need to use the RTC for deep sleep wake up, time keeping and sensing some buttons on RTC_GPIOs for forced wake ups from deep sleep.
The problem is that some times the crystal fails to start (?) resulting the module to not wake up when we trigger the RTC_GPIOs.

This does not happen to all modules.. We have modules bought different time periods but all report as ESP32D0WDQ6 (revision 1).
The "older" ones seem to not having this problem.. The latest ones do have this problem (I dont know how to figure out the product generation)

The crystal that we use now is :

https://www.digikey.com/product-detail/ ... ND/1237004

I have tried various load capacitors and the values that gave somehow a more stable behaviour was 18pf.
In menuconfig I have these values :
RTC clock source (External 32kHz crystal) --->
(3000) Number of cycles for RTC_SLOW_CLK calibration
(300) Bootstrap cycles for external 32kHz crystal

When the problem occurs I get in console :
-------------------------------------------------------------------------------------
I (0) cpu_start: App cpu up.
I (564) heap_init: Initializing. RAM available for dynamic allocation:
I (564) heap_init: At 3FFAE6E0 len 00001920 (6 KiB): DRAM
I (564) heap_init: At 3FFB9B90 len 00026470 (153 KiB): DRAM
I (565) heap_init: At 3FFE0440 len 00003AE0 (14 KiB): D/IRAM
I (565) heap_init: At 3FFE4350 len 0001BCB0 (111 KiB): D/IRAM
I (565) heap_init: At 40092438 len 0000DBC8 (54 KiB): IRAM
I (566) cpu_start: Pro cpu start user code
W (801) clk: 32 kHz XTAL not found, switching to internal 150 kHz oscillator
I (31) cpu_start: Starting scheduler on PRO CPU.
I (0) cpu_start: Starting scheduler on APP CPU.
...................................................................................................

the IDF Version is : v3.3-beta1-328-gabea9e4

I did found some other devs with this problem in the forum but no solution..
Have someone found a solution to this ?

thanks
Chris