In my latest research project I’m using the NXP FRDM-MCXN947 board. As part of that project I have to collect and export application trace data for later analysis. In that project I’m using the the Tracealyzer product from Percepio.

In this article I describe different ways to export trace data from the embedded target: using generic GDB commands or with an trace exporter in VS Code.

Outline

With Tracealyzer, the application gets instrumented to record system actions. I can stream the data for example using SEGGER RTT. Or I can record data in a ring buffer.

Using a ring buffer has the advantage that I can record data without a debug session. Then I can connect with the debugger and get the latest data in the buffer. Alternatively I can set a breakpoint in the ‘buffer full’ (OnTraceWrap()) callback and store the data at that point.

In this article, I’m using VS Code with NXP LinkServer based debugging on the FRDM-MCXN947 board. It works fine with cortex-debug and mcuxpresso-debug extensions.

Ring Buffer Trace configuration

In my application, I’m using a ring buffer to record the trace data.

For this, I initialize the trace library with

vTraceEnable(TRC_START);

McuLib Configuration

In this project, I’m using the McuLib with the following configuration:

/* FreeRTOS */
#define McuLib_CONFIG_SDK_USE_FREERTOS              (1)
#define configUSE_TRACE_FACILITY                        (1)
#define configGENERATE_RUN_TIME_STATS                   (1)
#define configGENERATE_RUN_TIME_STATS_USE_TICKS         (1)

/* Tracealyzer */
#define configUSE_PERCEPIO_TRACE_HOOKS                  (1) /* Percepio Tracealyzer */
#define McuPercepio_CONFIG_START_TRACE_IN_STARTUP_MODE  TRC_INIT /* TRC_INIT: only initialize trace, start it later with */
#define McuPercepio_CONFIG_RECORDER_MODE                TRC_RECORDER_MODE_SNAPSHOT /*TRC_RECORDER_MODE_STREAMING*/
#if McuPercepio_CONFIG_RECORDER_MODE==TRC_RECORDER_MODE_SNAPSHOT
    /* overwrite defaults in trcSnapshotConfig.h */
    #define TRC_CFG_SNAPSHOT_MODE                      TRC_SNAPSHOT_MODE_RING_BUFFER /* TRC_SNAPSHOT_MODE_STOP_WHEN_FULL */
    #define TRC_CFG_EVENT_BUFFER_SIZE                  (50)
#endif

Writing data with GDB

One way to export the data is using the GDB ‘dump’ command.

The code below in the callback creates a GDB dump command in the form of

dump binary memory <file> <hexStartAddr> <hexEndAddr>

void McuPercepio_OnTraceWrap(void)
{
  uint8_t buf[64];
  #define TRACE_DUMP_FILE_NAME   "trc.dump"

  /* GDB: dump binary memory <file> <hexStartAddr> <hexEndAddr> */
  McuPercepio_vGetGDBDumpCommand(buf, sizeof(buf), (unsigned char*)TRACE_DUMP_FILE_NAME);
  /* Hint: set a breakpoint on the exit of this function. Then use a gdb/debug console to execute the command in buf:
     eval "%s", buf
  */
}

With this, I can set a breakpoint and use the GDB ‘eval’ command to execute the command in the buffer, exporting the data to a file:

However, there are subtle differences how to execute the command, depending on the VS Code extension used:

• cortex-debug:
  eval \"%s\",buf
• mcuxpresso-debug:
  eval "%s",buf

TraceExporter for VS Code

Percepio makes a VS Code extension available here: https://percepio.com/traceexporter-for-vs-code/. I’m using the version 0.3.1 at the time of this article.

You need to install the extension as .vsix file.

With the extension, I can halt the target anywhere and then press the ‘Save Trace’ button:

The additional benefit of the extension is that I can press a button to view the trace data:

Make sure that the Percepio Tracealyzer executable is present in the PATH. This opens the Percepio Tracealyzer application with the exported data:

Summary

Traditionally, I have used generic GDB commands to export trace data. This works with command-line gdb or even with GDB in VS Code code. But if using VS Code, the Percepio Tracealyzer extension comes handy. With a button click I can export the data and with another button I can analyze the data. Which makes everything very easy.

Beside of using the proposed exporting methods: another one would be using semihosting, see https://mcuoneclipse.com/2026/06/01/semihosting-with-linkserver-in-vs-code/.

Happy tracing 🙂

Links

• Percepio Tracealyzer: https://percepio.com/tracealyzer/
• NXP VS Code Extension: https://www.nxp.com/design/design-center/software/development-software/mcuxpresso-software-and-tools-/mcuxpresso-for-visual-studio-code:MCUXPRESSO-VSC
• TraceExporter for VS Code: https://percepio.com/traceexporter-for-vs-code/
• FRDM-MCXN947: https://www.nxp.com/design/design-center/development-boards-and-designs/FRDM-MCXN947
• McuLib: https://github.com/ErichStyger/McuLib