Cortex-M JTAG Debugging (Verdin/Mallow)

Technical Support
1

I have an iMX8M Plus on a Mallow carier board. The board exposes the pins for a JTAG connector (X11). The document Cortex-M JTAG Debugging | Toradex Developer Center specifies in the supported HW that for a Verdin iMX8M Plus I would need a Verdin Devlopment Board or Dahlia carrier board.

This means that even soldering the missing connector on the Mallow board I would not have access to JTAG debugging via a J-Link probe?

Best regards

2

Hi, I’m the Toradex AI Assistant.

I might make mistakes or occasionally get you wrong. Our support team will step in if needed.

The documentation shows that JTAG debugging for Cortex-M on iMX8M Plus modules is supported on specific carrier boards(1). According to the official documentation, the supported boards include:

  • Verdin Development Board - X56 connector(1)
  • Dahlia Carrier Board - X8 connector(1)(2)

The Mallow carrier board is not explicitly listed in the supported hardware table for Cortex-M JTAG debugging(1). However, this doesn’t necessarily mean JTAG won’t work if you solder the connector.

Key Considerations

The JTAG interface operates at 1.8V(2) and requires specific signal routing and pull-up/pull-down configurations. For example, the Dahlia board shows these requirements(2):

  • JTAG_1_VREF: +1.8V reference output
  • JTAG_1_TCK: Pull-down on SOM
  • Standard 10-pin 1.27mm header connector

Potential Issues

If the Mallow board exposes the JTAG pins but isn’t officially supported, there could be:

  • Missing voltage level translation
  • Incorrect pull-up/pull-down resistor configurations
  • Signal integrity issues
  • Missing reference voltage output

Recommendation

Before proceeding with soldering, I’d recommend checking the Mallow carrier board schematic to verify:

  1. The JTAG signals are properly routed from the SODIMM connector
  2. Appropriate voltage levels and pull resistors are implemented
  3. The pinout matches the standard ARM JTAG 20-pin or Cortex Debug 10-pin connector

You can find carrier board design data and schematics on the Toradex Developer Website to compare the JTAG implementation between supported boards and the Mallow board.

Best regards, Toradex AI Assistant.

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3

As noted by AI, the Mallow board is not listed as compatible in the document you mentioned because the JTAG connector (X18) is not assembled by default. The Mallow X11 is not a JTAG connector, but a debug UART header.

If you solder the X18 header, you can use a J-Link with the Mallow board.

5

I mixed the connector names. I was actually referring to X18. I will in any case mount both connectors.

About the UART, I read that on iMX8M Plus, UART4 (the default debug channel for M7) in not available when linux is running because of a conflict with the BT/wifi drivers. Is there a workaroud for that or there is no other way to have access to the debug messages from the M7?

Best regards

6

On modules with Wi-Fi/Bluetooth, the UART_4 is shared with the Bluetooth UART. This means the UART_4 can only be used externally, if the Bluetooth UART is not in use.
In practice, to make this UART available for the M core, you need to remove all references to it from the Linux device tree.