JTAG detection failed for i.mx8mplus

[Bhardwaj]

We have been working on i.mx8mplus EVK while debugging getting an failed to connect to the target error. while debugging we observed on each and every pin of JTAG in oscilloscope then we found that TDO pin is 0.5v continuously. Do this create any issue?

             IDLE                   Debugging

-----------------------------------------------

VTRF: 1.8V(high)              1.8V(high)

TMS: 0V(low)                  high low(changing)

TCK: 0V(low)                  depends on CLK values

TDI: 1.8V(high)                data

TDO: 0.5V                        0.5V

Reset: 1.8V(high)           1.8V(high)

[Manuel_Salas]

Hello @Bhardwaj 

I hope you are doing very well.

Yes, the TDO signal must be aligned to the VTref ≈ 1.8 V.

Which debugger are you using?

According to the reference manual, the recommended procedure to start the JTAG controller is:

Also, you can try to follow the AN14367 (Debugging Cortex-A U-Boot and Native RTOS on i.MX 8M Plus and i.MX 93 EVKs).

Best regards,

Salas.

[Bhardwaj]

For JTAG Remote Control , What are the hardware changes to modify on  I.MX8MPLUS EVK?  

[Manuel_Salas]

Hello @Bhardwaj 

The JTAG Remote Control is controlled by signal REMOTE_SEL from FTDI IC.

You can take a look to this link about of remote debugging (i.MX93 as Example).

Best regards,

Salas.

[Bhardwaj]

hi salas,

we are using the prebuilt image given for SD card and booted the board from SD card. After stopping in uboot we have given the commands.

As you said we enabled the REMOTE_SEL pin using the below command

sudo .././bcu_Ubuntu20 set_gpio remote_en 1 -board=imx8mpevk

Then we have given the below command to check the remote debug is working or not

sudo src/openocd -s ./tcl -f interface/ftdi/imx8mp-evk.cfg -f board/imx8mp-evk.cfg

but we got the below mentioned error

Open On-Chip Debugger 0.12.0+dev-02241-g3fd975941 (2025-10-17-08:16)
Licensed under GNU GPL v2
For bug reports, read
http://openocd.org/doc/doxygen/bugs.html
Info : [imx8mp.a53.0] Hardware thread awareness created
Info : Listening on port 6666 for tcl connections
Info : Listening on port 4444 for telnet connections
Info : clock speed 1000 kHz
Error: JTAG scan chain interrogation failed: all zeroes
Error: Check JTAG interface, timings, target power, etc.
Error: Trying to use configured scan chain anyway...
Error: imx8mp.cpu: IR capture error; saw 0x00 not 0x01
Warn : Bypassing JTAG setup events due to errors
Error: Invalid ACK (0) in DAP response

we have observed the data is going on TDI and clock on TCK pin but no data is observed on TDO. The TDO pin is continuously low.

1. Why we are unable to connect the board in remote debug?

2. Do we need to enable any other pin in hardware?

3. what is the register should i read for jtag is enabled or disabled ?

4. we have worked on jtag debugging with remote debug and without debug(it means with JTAG Probe) , in both cases TDO is not responding correctly (data is not transfaring).

What should be the reasons for TDO behaving like that?

[Manuel_Salas]

Hello @Bhardwaj 

It make me think you have a hardware issue in your board.

Are you able to test the same in another board?

Best regards,

Salas.

[Bhardwaj]

Hi salas,

We are using Dstream-st debugger. We are doing the procedure mentioned in document. I have a doubt that

does the cortex-a53 can be detected after boot or not using jtag?

If not, can i know the procedure how the processor boot flow and when should i connect to target through jtag?