ESP32 Forum

Hi,

We are exploring programming the device(with WROOM module on it) using Jtag.

And this is what we are seeing.
The flash has to be first erased by doing "esptool.py erase_flash".
And then we can program the device using Jtag.
If we try to program brand new WROOM module using Jtag, it will fail with
------
Info : J-Link V10 compiled Jan 7 2019 14:00:10
Info : Hardware version: 10.10
Info : VTarget = 3.333 V
Info : clock speed 14000 kHz
Error: JTAG scan chain interrogation failed: all ones
------

So the WROOM module comes with default app programmed.
Is there a possibility that the default app interferes Jtag operation?
If so is there a way to work around?
We'd only want to use Jtag as a programming tool.

Can you also please confirm that
if we use ESP32 chip and SPI flash,instead of using WROOM module,
will we be able to program the SPI flash using Jtag from the beginning?

Thank you.

WROOM modules come with AT command application loaded, and that application configures GPIOs 12-15 as SPI slave interface, which makes it impossible to use JTAG.

If you are placing an order directly with Espressif, you may ask to get the modules programmed in a different way, i think.

Does this mean that JTAG debugging also is not possible unless / until the AT application has been removed via "esptool.py erase_flash?"

Secondly, how would one restore the AT application in future, should that be desired?