Can't get RTT working on L15 using J-Link Plus.

RE: Can't get RTT working on L15 using J-Link Plus.

Johnny Nguyen — Tue, 17 Jun 2025 23:12:24 GMT

Hello,

Just keeping this ticket up to date,

I've provided a minimal project and .hex (link) that has debugging and RTT logging enabled with a j-link plus, as well as steps on setting up the debug session and logging.

Can you try to recreate my setup and remove hardware/tool setup ambiguity?

Best regards,

RE: Can't get RTT working on L15 using J-Link Plus.

Calvin T — Tue, 17 Jun 2025 17:01:42 GMT

So I tried launching from the debug menu instead (up in the top left corner of the debug menu):

...instead of from the nRF Connect menu. So...progress! Still--same results: the log messages don't come through when I step.

RE: Can't get RTT working on L15 using J-Link Plus.

Calvin T — Tue, 17 Jun 2025 16:38:45 GMT

Gave it a try. Does that script get invoked when you select >Debug Launch build under the "Actions" menu in the nRF Connect tab?

I get asked whether I want to debug the core or the boot loader. I select "core," and get the same results I've been having (i.e. no RTT):

I think it's invoking the script...at least, when I look at the debug console, I see the options we have in the script:

RE: Can't get RTT working on L15 using J-Link Plus.

Johnny Nguyen — Tue, 17 Jun 2025 15:25:49 GMT

Hi Calvin,

I tested RTT debugging & logging with MCUBoot + BLE and do not see the same issues with my j-link plus, with the config to the .exe that Simon mentioned earlier.

For example, I quickly wrote a BLE application, and modified my launch executable to…

{

    "version": "0.2.0",

    "configurations": [

        {

            "type": "nrf-connect",

            "request": "launch",

            "name": "Launch basicble",

            "config": "c:/nrf/basicble/build/basicble",

            "runToEntryPoint": "main",

            "gdbServer": {

                "address": "127.0.0.1:${port}",

                "args": {

                    "if": "SWD",

                    "speed": 4000,

                    "device": "${device}",

                    "select": "usb=${snr}",

                    "port": "${port}",

                    "rtos": "${rtosPlugin}",

                    "jlinkscriptfile": "${jlinkScript}",

                    "additionalArgs": [

                        "singlerun",

                        "nogui",

                        "halt",

                        "noir",

                        "silent"

                    ]

                }

            }

        }

    ]

}

And each time I step, RTT is still printing logs as I step through

(with a sdc assert if I sit in a bp too long, since it's a bluetooth application)

Could you try modifying your debug configuration to see if the problem persists?

BR,

RE: Can't get RTT working on L15 using J-Link Plus.

Calvin T — Mon, 16 Jun 2025 15:00:32 GMT

I think we're talking apples and oranges. The contents of the launch.json in the .vscode subdirectory are as follows:

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "type": "nrf-connect",
            "request": "launch",
            "name": "Launch the active build configuration",
            "config": "${activeConfig}",
            "runToEntryPoint": "main"
        }
    ]
}

There's no "executable." I'm using nRF Connect and Toolchain 3.0, just in case that makes a difference.

RE: Can't get RTT working on L15 using J-Link Plus.

Susheel Nuguru — Mon, 16 Jun 2025 12:42:16 GMT

[quote user="Calvin T"]There's a launch.json under .vscode. Is that what you mean?[/quote]

Yes,

When you find settings for example "executable, try adding rttConfig settings as below as mentioned in that thread I linked to.

{
  "name": "Debug nRF54L15 + RTT",
  "type": "cortex-debug",
  "request": "launch",
  "servertype": "jlink",
  "device": "nRF54L15",
  "cwd": "${workspaceFolder}",
  "executable": "${workspaceFolder}/build/zephyr/zephyr.elf",
  "rttConfig": {
    "enabled": true,
    "address": "auto",
    "decoders": [
      { "type": "console", "port": 0 }
    ]
  }
}

RE: Can't get RTT working on L15 using J-Link Plus.

Calvin T — Fri, 13 Jun 2025 21:39:35 GMT

I'm sorry, I'm not sure I understand. There's a launch.json under .vscode. Is that what you mean? Or is there another file somewhere that is the vscode launch config you are referring to?

RE: Can't get RTT working on L15 using J-Link Plus.

Susheel Nuguru — Wed, 11 Jun 2025 19:47:43 GMT

We have seen some success like in this thread when you add rttconfig in vscode launch config. with address set to auto. Can you give it a try?

RE: Can't get RTT working on L15 using J-Link Plus.

Calvin T — Fri, 06 Jun 2025 21:49:07 GMT

Hi Simon,

We've discovered more information. The location of the RTT seems to shift around from the Boot loader to the Core. Here's a snapshot of the mcuboot and core map files. It appears that something is adding nrf_kmu_reserved_push_area to the core version, which is causing the RTT memory area to get remapped.

We are able to use J-Link RTT Viewer to explicitly set the RTT memory, but we have to disconnect and reconnect each time we run in order to get it to work. I haven't figured out a way to make it work in the nRF Connect IDE.

Please advise.

RE: Can't get RTT working on L15 using J-Link Plus.

Simonr — Thu, 05 Jun 2025 06:08:18 GMT

I think you might be looking in the wrong place here. The RTT terminal in VS Code selects a generic M33 as the target in the gdb server, and needs to be changed to nRF54L15. Here are some images:

Best regards,

Simon

RE: Can't get RTT working on L15 using J-Link Plus.

Calvin T — Tue, 03 Jun 2025 14:57:07 GMT

No worries, Simon.

Here's my launch directive:

"launch": {

"version": "0.2.0",

"configurations": [

{

"type": "nrf-connect",

"request": "launch",

"name": "Launch core",

"config": "${workspaceFolder}/core/build/core",

"runToEntryPoint": "main"

}

]

}

As you can see, there's no serverArgs directive.

RE: Can't get RTT working on L15 using J-Link Plus.

Simonr — Mon, 02 Jun 2025 05:29:23 GMT

Hmm, okay that's strange. Can you check out this ticket and try my colleague Amanda's suggestion as there seem to have been some changes to RTT logging on the latest VS Code extension versions. RTT debugging not working on nrfConnect for vs Code 2025.4.106

Let me know if that makes a difference for you or not. Sorry about the late reply by the way, but last week had a bank holiday here in Norway, so we've been a bit short staffed.

Best regards,

Simon

RE: Can't get RTT working on L15 using J-Link Plus.

Riley-Cameron — Tue, 27 May 2025 17:25:58 GMT

Hello Simon,

I am one of Calvin's coworkers. We were able to get RTT working again after a normal flash, however when debugging (with & without reflashing) RTT does not work at all.

Do you have any advice for getting RTT to come through during debugging?

Thanks!

Riley

RE: Can't get RTT working on L15 using J-Link Plus.

Calvin T — Tue, 27 May 2025 16:00:22 GMT

CONFIG_LOG_BACKEND_RTT is set to Y.

Yes, the same exact project and setup was used. We're using dev boards from the same rev. Further, I've tried with multiple different dev boards. We're using our own dev boards, but the boards aren't complicated and they work fine with my colleague's setup.

I can't swap boards with him easily, because he's in Italy at the moment. However, I'm having another engineer here in the office try. I'll update as soon as we have some results.

RE: Can't get RTT working on L15 using J-Link Plus.

Simonr — Mon, 26 May 2025 06:37:40 GMT

Okay, nothing obvious in the differences on the systems. What sample project are you trying to run, and can you confirm the CONFIG_LOG_BACKEND_RTT is set to Y in your project? It should default to Y if CONFIG_SHELL_LOG_BACKEND is not enabled, and if the following dependencies are set correctly:

CONFIG_USE_SEGGER_RTT && !CONFIG_LOG_FRONTEND_ONLY && !CONFIG_LOG_MODE_MINIMAL && CONFIG_LOG

Did your colleague also use the same exact project and setup to get it up and running? And are you using the same nRF54L15 DKs? If not, what version numbering is there on the DKs? I can also try to recreate this on my end if you let me know what steps you've done.

Best regards,

Simon

RE: Can't get RTT working on L15 using J-Link Plus.

Calvin T — Fri, 23 May 2025 14:40:02 GMT

And, yes--this was done through the nRF Connect extension.

RE: Can't get RTT working on L15 using J-Link Plus.

Calvin T — Fri, 23 May 2025 14:32:28 GMT

My system:

nrfutil:

91 0.5.0 Not installed
ble-sniffer 0.16.2 Not installed
completion 1.4.0 1.5.0 Upgradeable
device 2.11.0 2.11.0 Installed
npm 0.3.0 Not installed
nrf5sdk-tools 1.0.1 1.1.0 Upgradeable
sdk-manager 1.3.0 Not installed
suit 0.9.0 Not installed
toolchain-manager 0.15.0 Not installed
trace 4.0.1 Not installed

Segger J-Link 8.32

J-Link Compact PLUS V12.00

Jesse's system:

nrfutil:

91 0.5.0 Not installed

ble-sniffer 0.16.2 Not installed

completion 1.5.0 1.5.0 Installed

device 2.7.12 2.11.0 Upgradeable

npm 0.3.0 Not installed

nrf5sdk-tools 1.1.0 1.1.0 Installed

sdk-manager 1.3.0 Not installed

suit 0.9.0 Not installed

toolchain-manager 0.15.0 Not installed

trace 4.0.1 Not installed

Segger J-Link 8.28

J-link Compact PLUS V11.00

RE: Can't get RTT working on L15 using J-Link Plus.

Simonr — Thu, 22 May 2025 13:48:06 GMT

Please confirm what version of the J-Link firmware is installed on your computer. I assume this log is within the VS Code extension, correct, or do you use a dedicated J-Link RTT viewer here? Also compare J-Link version your colleague has.

Best regards,

Simon

RE: Can't get RTT working on L15 using J-Link Plus.

Calvin T — Wed, 21 May 2025 20:51:41 GMT

Oh--my colleague who is able to make it work is using the same codebase, but they're on a Mac. I'm using a Windows box.

RE: Can't get RTT working on L15 using J-Link Plus.

Calvin T — Wed, 21 May 2025 20:48:00 GMT

J-Link firmware is v12.00, dated April 1st 2025.