i.MX 8M Plus debug mode not working

[Gfrari]

I would like to access the internal registers via the ARM DAP using JTAG. The following is written in the Reference Manual::

- Debug mode: JTAG_MOD == 0, DAP is the only TAP controller in the daisy chain
- Test mode: JTAG_MOD == 1, SJC is the only TAP controller in the daisy chain.

I was able to successfully test the test mode (JTAG_MOD = 1). The instruction register length is 5 bit (IRSHIFT) and I was also able to read the device ID (DRSHIFT).

Unfortunately the debug mode (JTAG_MOD = 0) does not work. The instruction register length is still 5 bit and not 4 bit as expected for the ARM DAP. Also the Device ID is still the same and not the ARM ID as expected.

It looks as if the switch to the debug mode not working.

The BOOT_MODE0-3 pins are all = 1.

Are there any other conditions that have to be fulfilled to use the debug mode?

Many thanks

[Alejandro_Salas]

Hello @Gfrari 

I hope you are doing well.

I would like to ask, which device are you using to boot the i.MX8MP?

You can see on the Reference Manuel there is not an option to BOOT_MODE0-3 = 1:

Could you please double check this?

Also, please check the JTAG_MOD pin is really in 0 state and is not fluctuating.

Best regards,

Salas.

[Gfrari]

Hello @Alejandro_Salas 

thanks for your reply.

I got the information for the BOOT_MODE0-3 pins from here:

https://community.nxp.com/t5/i-MX-Processors/i-MX8M-Plus-Coresight-Access/m-p/1932863

And the JTAG_MOD pin is really 0.

Best regards

[Alejandro_Salas]

Hello,

Sure, the BOOT_MODE pines are 0b1111 to enter to Boundary Scan mode, please take a look to the chapter 5.4 Boundary scan operation of the IMX8MPHDG (attached).

Best regards,

Salas.

[Gfrari]

Hello,
as i already mentioned in the initial request, the JTAG Boundary Scan Mode is already working.
I need to get the "DEBUG" Mode (JTAG to the Core Logic) running. Therefor the JTAG_MOD Signal has to be 0.
The reference manual says that in JTAG_MOD = 0 mode, the ARM DAP is the only TAP in the chain. But this does not work.
As i sad, it seems like the chain selection with the JTAG_MOD does not work correctly. The Chain Length does not change from 5 to 4 and the DRSHIFT shows that still the SJC Idcode is loaded. The Chip is complete "new", which means currently is no valid boot image programmed in the flash.
It feels like a missbehaviour from the chip, or a currently unknown condition to get the ARM DAP in the chain. The information from the reference manuals are not working.
Best Regards