ESP32 - JTAG Non-Functional w/ Stock Firmware

tiradedepirate
Posts: 8
Joined: Tue Jan 15, 2019 5:12 am

ESP32 - JTAG Non-Functional w/ Stock Firmware

Postby tiradedepirate » Sun Oct 06, 2019 8:53 pm

Hello Everyone,

I purchased 4 raw ESP32-WROOM-32 modules from Digi-key, soldered them to my hardware, and then attempt to flash them over the JTAG interface. Every attempt of programming the module left me with the dreaded all ones seen blah blah blah error.

All of the existing documentation online suggested a hardware fault so I went into hardware troubleshooting mode until I became fully confident the hardware was not an issue. After much thrashing around, I finally noticed the module were pre-programmed as they were dumping data over the UART port. I managed to re-flash the hardware using the UART interface instead and then the JTAG interface was accessible.

This left me with the following understanding:
1. It's possible for the firmware to "brick" the JTAG interface
2. ESP32 modules from espressif can potentially come with firmware pre-installed.

I have a few questions:
1. Can the existing OpenOCD scripts be modified to some how latch the JTAG interface before the user application disables it? I'm looking how to avoid this issue in manufacturing without switching to the UART interface. I'm also concerned with users potentially locking themselves out of the product if they incorrectly program the device.
2. Can Espressif please add a warning / disclaimer to their Github page for JTAG or the ESP32's datasheet.

Thanks,
Tyler

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krzychb
Posts: 232
Joined: Sat Oct 01, 2016 9:05 am
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Re: ESP32 - JTAG Non-Functional w/ Stock Firmware

Postby krzychb » Mon Oct 07, 2019 4:49 am

tiradedepirate wrote: 1. Can the existing OpenOCD scripts be modified to some how latch the JTAG interface before the user application disables it? I'm looking how to avoid this issue in manufacturing without switching to the UART interface. I'm also concerned with users potentially locking themselves out of the product if they incorrectly program the device.
2. Can Espressif please add a warning / disclaimer to their Github page for JTAG or the ESP32's datasheet.

Hello tiradedepirate,

1. I do not think so. Please see https://esp32.com/viewtopic.php?f=13&t= ... 837#p49837

2. Yes, JTAG documentation will be updated!

Sorry for the headache and thank you for taking time to document this issue!

tiradedepirate
Posts: 8
Joined: Tue Jan 15, 2019 5:12 am

Re: ESP32 - JTAG Non-Functional w/ Stock Firmware

Postby tiradedepirate » Mon Oct 07, 2019 5:30 pm

Thanks @krzychb for the quick reply. :)
I found another post which the author said he could erase the firmware via JTAG, and then program.

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