Some STM32 do not like JTAG debugging

[Uwe Bonnes]

Beside my Nucleo-H7S3L8 board, I have other boards where the MCU can do JTAG and have JTAG pin accessible, but neither STM32CubeProgrammer not OpenOCD and other programmers can detect/attach  via JTAG. SWD works works fine on these boards

Here the output of the Log window of STM32CubeProgrammer of two similar boards with  STM32L412KB chips with full JTAG connections, NJRST pin is left unconnected. First I connected the jtag-detectable board, than the undetectable:

15:44:20 : STM32CubeProgrammer API v2.16.0 | Linux-64Bits 
  15:44:26 : UR connection mode is defined with the HWrst reset mode
  15:44:26 : ST-LINK SN  : 51FF6D064888524933312587
  15:44:26 : ST-LINK FW  : V2J43S7
  15:44:26 : Board       : --
  15:44:26 : Voltage     : 3,24V
  15:44:26 : JTAG freq   : 9000 KHz
  15:44:26 : Connect mode: Under Reset
  15:44:26 : Reset mode  : Hardware reset
  15:44:26 : Device ID   : 0x464
  15:44:26 : Revision ID : Rev A
  15:44:26 : Debug in Low Power mode enabled.
  15:44:26 : UPLOADING OPTION BYTES DATA ...
  15:44:26 :   Bank          : 0x00
  15:44:26 :   Address       : 0x40022020
  15:44:26 :   Size          : 20 Bytes
  15:44:26 : UPLOADING ...
  15:44:26 :   Size          : 1024 Bytes
  15:44:26 :   Address       : 0x8000000
  15:44:26 : Read progress:
  15:44:26 : Data read successfully
  15:44:26 : Time elapsed during the read operation is: 00:00:00.006
  15:44:43 : Error: Unable to get core ID
  15:44:43 : Error: Unable to get core ID
  15:44:43 : Error: Unable to get core ID
  15:44:43 : Warning: Connection to device 0x464 is lost
  15:44:44 : Disconnected from device.
--- Connect to other board!
  15:44:55 : UR connection mode is defined with the HWrst reset mode
  15:44:55 : ST-LINK SN  : 51FF6D064888524933312587
  15:44:55 : ST-LINK FW  : V2J43S7
  15:44:55 : Board       : --
  15:44:55 : Voltage     : 3,26V
  15:44:55 : ST-LINK error (DEV_UNKNOWN_MCU_TARGET)
  15:44:55 : ST-LINK SN  : 51FF6D064888524933312587
  15:44:55 : ST-LINK FW  : V2J43S7
  15:44:55 : Board       : --
  15:44:55 : Voltage     : 3,26V
  15:44:55 : Error: ST-LINK error (DEV_UNKNOWN_MCU_TARGET)

 On both boards, e.g. openocd with a low level debugger can detect the chain via JTAG, but the undetectable board on the next access to a DP  register all high bits are returned, also for the ACK bits.

[MNapi]

what kind of st link are you using ?

I had bunch oft those cheap knock offs from eBay, some work, some did not.

Since I got original STLINK-V3, I have never had problem with connection.

the same goes for ST Links which come with original boards always work

ST does not give source code to make own ST link so all of the are some hacked copies which do not seem to works 100%.

[Andrew Neil]

Does your app "steal"  any of the GPIO pins needed for JTAG ?

---

@Uwe Bonnes wrote:

NJRST pin is left unconnected. .

---

Does connecting it fix the problem?

[Uwe Bonnes · Accepted solution]

A real white external STLink.

But my fault: The board revision that did not do JTAG has reused TDI. So at least the problem with STM32L412 is solved. I should have looked at the schematic mor carefully!

[Uwe Bonnes]

And now I see that SB27 on Nucleo-H7S3L8 is DNF and so JTAG is not possible w/o modification on NUCLEO-H7S3L8 too.

[Uwe Bonnes]

Bootloader code and a startup firmware is available on the net. After initial programming, ST updater can keep that thing  up-to-date. But clones with different or wrong wiring float around ...