GPIO32 and GPIO33 on DevkitC V4 (Wroom)

stefanct
Posts: 5
Joined: Sun Mar 18, 2018 1:48 pm

GPIO32 and GPIO33 on DevkitC V4 (Wroom)

Postby stefanct » Sun Mar 18, 2018 3:41 pm

Hi,
I was unable to confidently derive from (the schematics in) the documentation if there is a 32kHz crystal attached to the RTC GPIO pins 32 and 33 of the ESP32 DevkitC V4. In earlier versions of the Wroom datasheet (ESP-WROOM-03 Specifications, Version 1.0, 2015.12) there is one depicted but not in the current version. Can you please clarify in which models there is (n)one?

The reason why I was investigating this question at all was because I was trying to use the pins as GPIOs and noticed very erratic behavior (exceptions, reboot loops etc) when doing so. Eventually I came to the conclusion that the RTC GPIO pins have to be switched to general general purpose pins (thanks to some bits in the forum). To use them I had to configure them normally with gpio_config() but additionally change their functionality with rtc_gpio_deinit(). As far as I can tell this changes bits 17 and 18 of RTCIO_XTAL_32K_PAD_REG to 0. However, according to the datasheet this is the reset value (Register 4.52 in the ESP32 Technical Reference Manual, Version 2.9). So I conclude that something in the firmware generated by the IDF enables the RTC muxing before my application starts. This seems to be a bug to me if the RTC functionality cannot/is not used anyway on my hardware and should be more clearly documented as it was very surprising. What is responsible for the RTC functionality to be enabled by default?

ESP_igrr
Posts: 1596
Joined: Tue Dec 01, 2015 8:37 am

Re: GPIO32 and GPIO33 on DevkitC V4 (Wroom)

Postby ESP_igrr » Sun Mar 18, 2018 4:44 pm

Hi stefanct,
stefanct wrote:Can you please clarify in which models there is (n)one?
DevKitC board (all versions of them) come with ESP-WROOM32 module, not ESP-WROOM03. None of the versions of ESP-WROOM32 came with a 32k XTAL. DevKitC boards don't come with 32k XTAL installed either.
stefanct wrote:As far as I can tell this changes bits 17 and 18 of RTCIO_XTAL_32K_PAD_REG to 0. However, according to the datasheet this is the reset value (Register 4.52 in the ESP32 Technical Reference Manual, Version 2.9).
With default settings in sdkconfig file, RTCIO_XTAL_32K_PAD_REG is set to 0x84100010 at application startup (app_main), so both these bits are 0. If you add a line

printf("RTC_IO_XTAL_32K_PAD_REG=0x%08x\n", REG_READ(RTC_IO_XTAL_32K_PAD_REG));

near the top of app_main, (and also include "soc/rtc_io_reg.h"), do you see a different value?
(Note that a long time ago, before IDF version 2.0-rc1, some startup code indeed initialized GPIOs 32 and 33 as RTC IOs. As far as I can tell, this is no longer the case.)

stefanct
Posts: 5
Joined: Sun Mar 18, 2018 1:48 pm

Re: GPIO32 and GPIO33 on DevkitC V4 (Wroom)

Postby stefanct » Sun Mar 18, 2018 6:29 pm

ESP_igrr wrote:
stefanct wrote:Can you please clarify in which models there is (n)one?
DevKitC board (all versions of them) come with ESP-WROOM32 module, not ESP-WROOM03. None of the versions of ESP-WROOM32 came with a 32k XTAL. DevKitC boards don't come with 32k XTAL installed either.
Oh, I was not aware that "03" was a model name. Everything's clear now. Sorry.
ESP_igrr wrote:
stefanct wrote:As far as I can tell this changes bits 17 and 18 of RTCIO_XTAL_32K_PAD_REG to 0. However, according to the datasheet this is the reset value (Register 4.52 in the ESP32 Technical Reference Manual, Version 2.9).
With default settings in sdkconfig file, RTCIO_XTAL_32K_PAD_REG is set to 0x84100010 at application startup (app_main), so both these bits are 0. If you add a line

printf("RTC_IO_XTAL_32K_PAD_REG=0x%08x\n", REG_READ(RTC_IO_XTAL_32K_PAD_REG));

near the top of app_main, (and also include "soc/rtc_io_reg.h"), do you see a different value?
(Note that a long time ago, before IDF version 2.0-rc1, some startup code indeed initialized GPIOs 32 and 33 as RTC IOs. As far as I can tell, this is no longer the case.)
Interesting. I do indeed now get the same readout before and after calling rtc_gpio_deinit() (RTC_IO_XTAL_32K_PAD_REG=0x84100010) but I have updated IDF in the meantime unfortunately because I was relatively sure about it - but did not actually check the register values. But the update was only from the state of the master branch on github about a month ago to the current HEAD version. I'll try to investigate and reproduce the problem. Thanks for your insights so far!

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