ESP32 Forum

Dear,

I would like to ask how to enable the external JTAG(ESP-PROG). At default the efuse bits are set to EFUSE_STRAP_JTAG_SEL=1, FUSE_DIS_USB_JTAG=0, EFUSE_DIS_PAD_JTAG=0, this means that the selection is made on the state of GPIO3, for which we use a pull-up. This should mean "USB Serial/JTAG controller" is selected and I suppose its the external JTAG?

However, at this point the external JTAG didn't work, but after trying the on-chip JTAG, I could successfully connect. This was the first strange behaviour.

Then we have tried to set EFUSE_DIS_PAD_JTAG=1, which should set the external JTAG regardless to the state of GPIO3.

In the efuse table nothing matches exactly this name as it is stated in the datasheet and where the most similar have been:
DIS_USB_JTAG (BLOCK0) Disable usb_serial_jtag-to-jtag function = True R/W (0b1)
DIS_USB_SERIAL_JTAG (BLOCK0) Disable usb_serial_jtag module = False R/W (0b0)
and as it is visible we have set the DIS_USB_JTAG=1. After this we could neither anymore connect through the on-chip JTAG, neither the external JTAG.

Can you please speficfy which efuses are referred to the external JTAG and which to the on-chip, or where is the catch that its imposible to make the external JTAG work?

To my understanding, "USB Serial/JTAG controller" is the on-chip JTAG via ESP USB D+ D- pin. PAD_JTAG is external JTAG which connects to ESP32 TMS, TDI, TDO...
set EFUSE_DIS_PAD_JTAG=1 will permanently disable external JTAG,
set EFUSE_DIS_USB_JTAG=1 will permanently disable on-chip JTAG via USB.

To help anyone finding this later, EFUSE_STRAP_JTAG_SEL is 0 be default, not 1 as per the OP. By default, GPIO3 is ignored.