ESP32 Forum

I am trying to figure out how to boot the ESP32-S3-WROOM-1 to download mode mode from USB JTAG and have read in the documentation that boot behavior is also controlled by the eFuse registers, in particular the following: EFUSE_DIS_USB_JTAG, EFUSE_DIS_PAD_JTAG, and EFUSE_STRAP_JTAG_SEL. However, I don't know if I need to set those values using the eFuse peripheral or if they have default values which will allow me to boot to download mode setting the USB JTAG as the boot source.

I could not find default values for eFuse in the reference manual, but I might have missed it.

Are the default values known and if so what are they for the following registers?
EFUSE_DIS_USB_JTAG, EFUSE_DIS_PAD_JTAG, and EFUSE_STRAP_JTAG_SEL

Can I assume that if the following strapping pins are set as follows the device will boot to JTAG USB?
GPIO0 = 0
GPIO46 = 0
GPIO3 = 1

Thank you in advance

Normally, eFuses are always 0 as you can only make it 1 by blowing them, but once they're blown you can never revert them to 0.

From the factory, the S3 will by default have the USB-jtag-serial device active. (But do note that an application can swap that for the DWC-USB device for the runtime of that application, e.g. if it uses TinyUSB. But given the default fuses, resetting to bootloader will always show the USB-serial-JTAG device again.)

Thank you for the reply. That makes sense. If the default configuration configures enables booting to USB JTAG, then what is the reason to have the gpio3 strapping pin?

That GPIO is indeed only relevant if EFUSE_STRAP_JTAG_SEL is blown.

That makes sense. Thank you.