ESP32 Boot Mode Message

[jtrexr2]

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.

[ESP_Sprite]

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]

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]

https://github.com/espressif/esptool/wi ... -Selection

[jtrexr2]

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]

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]

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