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DEBUG.md

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Debugging and Flashing nRF5x

Downloading the JLink Utilities

The JLink Software and Documntation Pack is the place to get Segger debug utilities at the time of this writing. OSX, Linux, Windows, even ARM Linux versions are there. Quite impressive. I use the OSX version. The Linux version is nearly identical.

Jlink Commander (on OSX and Linux this is called JLinkExe)

See script nrf/scripts/jlink-nrf

  • OSX: /Applications/SEGGER/JLink/JLinkExe
  • Linux: /opt/segger/jlink (or where ever ...)

JLinkRTTClient

Note that JLinkRTTClient is a telnet program. Telnet seems to work just as well.

To get the Jlink RTT Client running, JLink Commander JLinkExe or the JLink GDB Server JLinkGDBServer needs to be running first.

A script nrf/scripts/jlink-nrf provides a short cut for the command line invocation. After running JLinkExe the JLinkRTTClient can be started and will find the telnet port to connect. Starting JLinkRTTClient first does not seem to work.

If JLinkExe is terminated then JLinkClient will need to restart.

JLinkRTTLogger

JLinkRTTLogger works in a similar manner as JLinkClient, however JLinkRTTLogger uses the default Segger RTT channel 1 and these projects use channel 0. JLinkRTTLogger seems to reconnect properly with the starting and stoppping of JLinkExe; unlike JLinkClient.

jlink_rules.mak

  • Provides several rules for programming the nRF52 development boards.

    • Only the nRF52832/PCA10040 is supported right now.
    • It should not be hard to support the nRF52840/PCA10056.

  • make jlink-help provides rule specific command information.

  • To program the application onto the nRF52 board: make flash

    Note: This rule has a dependency on TARGET_NAME.hex (where TARGET_NAME is project name being built.) So building this target will update the compile object files, elf .out and .hex files, but not the .lst and .dump.txt files. The makefile rules could use a little tweaking here. Use the rule make all to insure all of the final targets are up to date.

Note: Attempting to flash the nRF boards while the jlink RTT client is attached causes the NRF boards to hang. If this happens, drop the RTT client and disconnect the board USB. Reconnect the USB and start over.

.segger_sn file

When initiating multipe gdb servers through the use of JLinkGDBServer the target device may be specified on the command line using Segger SWD interface hardware serial number. To make this process more conenient I incorporate files .segger_sn in the ble_central and ble_peripheral working directories. Since these files will be different for each user they are not checked in. Instead you will find them in the .gitignore file for this project. If the files do not exist then the jlink_rules.mak will ignore them by not including them. If they do exist then the Segger serial number specified by the .segger_sn file will be the target of the debug session.

The SWD interface hardware Serial Number is a 9 digit numeric value usually prominently displayed on Segger hardware. This value may be obtained from the JLink Commander JLinkExe tool. With only target connected, run JLinkExe and it will connect and display the serial number. The JLinkExe command conf will show the serial number again.

Typical .segger_sn contents are:

# nrf/ble_central/.segger_sn
# Assign the SEGGER Serial Number used for debugging the ble_central project.
SEGGER_SN=123456789

The format is Makefile syntax.

More information is available in my github gist: JLinkGDBServer Multiple Sessions

gdb

  • jlink_rules.mak

    Provides a rules for programming and running the gdb server on the NRF board. Again, right now the nRF52832/PCA10040 is set with symbols in this file as is the softdevice s132.

    The jlink-rules.mak contains gdb specific settings in the JLINK_GDB_OPTS symbol. Change these as needed.

  • gdb initialization

    The gdb server setting must be matched with the gdb client settings. Using a gdb initialization file makes connecting and setting up gdb faster and easier. Each project which runs under gdb contains a gdb-init file which is checked into git. An example:

      target remote localhost:2331
  file _build/<targetname.out>
  load
  monitor reset

    It should be noted that the ble_central/gdb-init file differs from the others; its port assignment is 2431. This matches the GDB_PORT value set in the Makefile which is used by jlink-rules.mak. This allows for simultaneous debugging of the ble_peripheral and ble_central projects.

    There is a Makefile target gdb-server which can be invoked:

      $ make gdb-server

    Which will start the gdb server. Once started, the server can be attached to using:

      $ <path>/gcc-arm-none-eabi/bin/arm-none-eabi-gdb --quiet --command=./gdb-init

JLinkRTTClient

The logger class within the nrf projects uses the JLinkRTTClient for outputting debug, info, warning and error information. There is a Makefile target rttc which should allow you to easily get the RTTC output in a shell:

$ make rttc

Monitor Mode Debugging

When you halt the Noridc softdevice, typically through a break point in the debugger, guess what happens: Noridc throws you an assert via an interrupt into their softdevice handler and the only way to recover is through a reset of your device.

There is a work-around call monitor mode debugging. Monitor Mode Debugging with J-Link and GDB/Eclipse

Disclaimer: I have yet to try this.