ESP32 Boot Mode Message

jtrexr2
Posts: 4
Joined: Wed Apr 01, 2020 4:21 pm

ESP32 Boot Mode Message

Postby jtrexr2 » Wed Apr 01, 2020 5:47 pm

Hello,

I have developed a custom ESP32-based industrial sensing platform, and am running into the following issue on a new revision of our main product design. After successfully flashing our ESP32 using a CP2104-based PCB and using the pre-built msys make tools, we are able to boot into the software correctly. However, after a hard power cycle, the ESP32 stays in bootloader mode and prints the following message:

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rst:0x1 (POWERON_RESET),boot:0x5 (DOWNLOAD_BOOT(UART0/UART1/SDIO_FEI_REO_V2))
waiting for download
I've scoped the ESP_EN and GPIO0 lines to check their behavior, and from my interpretation of the boot modes, they are correct. I've attached a couple of photos showing this behavior, where the blue line is the ESP_EN line rising to 3V3, and the yellow line is GPIO0. In 0_1uF_en.jpg, the ESP_EN line has a 0.1uF capacitor to GND. I was worried about rise times and maybe the ESP32 sampling GPIO0 too early, so 1uF_en.jpg shows the result after I swapped this for a 1uF capacitor to GND.

According to the ESP32 Boot Mode Selection webpage, the example bootloader message should give the strapping register as

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boot: 0x3
, so I'm a little confused on why its is now a 0x5. Any insight or help would be greatly appreciated. If there's a better place to post this question, please let me know.
Attachments
0_1uf_en.jpg
0_1uf_en.jpg (1.16 MiB) Viewed 2755 times
1uf_en.jpg
1uf_en.jpg (1.14 MiB) Viewed 2755 times

ESP_Sprite
Posts: 3461
Joined: Thu Nov 26, 2015 4:08 am

Re: ESP32 Boot Mode Message

Postby ESP_Sprite » Thu Apr 02, 2020 7:47 am

Not that it should matter, but any idea why your EN line starts at 1.5V? Also, if you reset the chip by manually driving EN low, does it boot correctly?

Also, the difference between boot mode 3 and 5 is that GPIO15 is low at 3 and high at 5.

jtrexr2
Posts: 4
Joined: Wed Apr 01, 2020 4:21 pm

Re: ESP32 Boot Mode Message

Postby jtrexr2 » Mon Apr 06, 2020 4:36 pm

I will check the voltage level of the EN line, but it appears to only be an issue when a programmer is attached and we're attempted to flash/reset via the RTS/CTS.

Out of curiosity, could the changing behavior of GPIO15 cause any issues with boot?

chegewara
Posts: 1067
Joined: Wed Jun 14, 2017 9:00 pm

Re: ESP32 Boot Mode Message

Postby chegewara » Tue Apr 07, 2020 1:49 am


jtrexr2
Posts: 4
Joined: Wed Apr 01, 2020 4:21 pm

Re: ESP32 Boot Mode Message

Postby jtrexr2 » Tue Apr 07, 2020 2:37 pm

Thanks, I referenced the boot modes in my post. My main concern was whether the boot mode listed as 0x05 instead of 0x03 was indicative an issue that would prevent booting.

chegewara
Posts: 1067
Joined: Wed Jun 14, 2017 9:00 pm

Re: ESP32 Boot Mode Message

Postby chegewara » Wed Apr 08, 2020 7:43 am

0x02 - MTDO (GPIO15)
....
15 (MTDO) If driven Low, silences boot messages printed by the ROM bootloader. Has an internal pull-up, so unconnected = High = normal output.
As you can see its used to silence boot messages and can be either LOW or HIGH. Its very unlikely it will prevent booting unless there is bug in bootloader.

jtrexr2
Posts: 4
Joined: Wed Apr 01, 2020 4:21 pm

Re: ESP32 Boot Mode Message

Postby jtrexr2 » Wed Apr 08, 2020 3:16 pm

Yes thank you, that's the purpose of my question.

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