Eclipse with GDB is great: it comes with a graphical front end for debugging. But sometimes it is all about to download a program. Is it really necessary to launch an IDE like Eclipse to program or quickly debug a board? With the GNU Debugger (GDB), the answer is ‘no’: GDB comes with a command line debugger which is designed exactly for this: providing a command line interface for programming/downloading and debugging, bypassing any GUI (Graphical User Interface).

Outline

In “OpenOCD/CMSIS-DAP Debugging with Eclipse and without an IDE” I have documented how this works with the combination of GDB+OpenOCD+CMSIS-DAP, but this works in a similar way with Segger J-Link and P&E Multilink, as both come with a GDB server implementation too (e.g. if I use the Freescale Kinetis Design Studio or a DIY Eclipse IDE).

What I need is:

• The GDB client: this comes with the GNU tools, e.g. the GNU ARM Embedded (launchpad).
• The GDB server (e.g. from P&E or Segger). Both come installed with the Kinetis Design Studio.
• And a board :-). I use here the FRDM-KL25Z board as it works with P&E, Segger, and OpenOCD/CMSIS-DAP GDB servers.

GDB Debugging Chain

To debug with GDB, I need a client, a server, a probe and of course a board:

The client is the gdb executable (arm-none-eabi-gdb.exe) on the host. It talks over a TCP/IP connection/port to the GDB server. The server is usually an executable running on the same machine, but it can run anywhere in the network too on a remote machine. Popular GDB servers are available from Segger, P&E or as well as open source (e.g. OpenOCD, see “OpenOCD/CMSIS-DAP Debugging with Eclipse and without an IDE“). Kinetis Design Studio v2.0.0 comes with all these three servers. The server needs to talk to the microcontroller/device/board using a JTAG/SWD connection: this can be a probe from vendors like Segger (J-Link, for example), P&E (USB Multilink, for example) or with CMSIS-DAP (e.g. on the FRDM-KL25Z board, see https:\\www.freescale.com\opensda). Both Segger and P&E provide firmware files for the FRDM boards to behave like a hardware probe, see “Segger J-Link Firmware for OpenSDAv2” and “New P&E OpenSDA Firmware v114“.

GDB Client

The GDB client for ARM is named arm-none-eabi-gdb.exe, and in the case of KDS V2.0.0 it is located inside the toolchain\bin folder:

start the GDB client with

arm-none-eabi-gdb.exe

The GDB client can be used with many GDB servers. The Segger and P&E specifics will be handled after this section.

P&E GDB Server

There is a GDB server from P&E available from http://www.pemicro.com/products/product_viewDetails.cfm?product_id=15320151. Alternatively, a P&E GDB server is included in the Freescale Kinetis Design Studio (KDS) (https://www.freescale.com/kds).

In case of KDS V2.0.0, the P&E GDB server is inside the eclipse\plugins\com.pemicro.debug.gdbjtag.pne folder. The folder name depends on the version, and there is a sub folder depending on Windows or Linux (win32 on Windows). The GDB server is named ‘pegdbserver_console.exe’:

The most important command line arguments are:

• -startserver: starts the server
• -device: specifies the device
• -devicelist: lists the supported devices

These and other command line options are documented in
<KDS_2.0.0>\pemicro\Kinetis_Design_Studio_Debug_Configuration_User_Guide.pdf

To find out the list of supported devices, use the -devicelist command:

💡 the real path to the P&E gdb server depends on your version installed. I’m using KDS v2.0.0

pegdbserver_console.exe -devicelist

I start the server for the device on the FRDM-KL25Z on a cmd/DOS prompt with

pegdbserver_console.exe -startserver -device=KL25Z128M4

and it will report something like this:

P&E GDB Server, Version 5.13.02.00
Copyright 2014, P&E Microcomputer Systems Inc, All rights reserved

Loading library C:\Freescale\KDS_2.0.0\eclipse\plugins\com.pemicro.debug.gdbjtag
.pne_1.1.8.201411191655\win32\gdi\unit_ngs_arm_internal.dll ... Done.

Command line arguments: -startserver -device=KL25Z128M4
Device selected is kl25z128m4
PE-ERROR: Unable to auto-detect debug hardware. Please specify on the command-line. Halting.

C:\Freescale\KDS_2.0.0>eclipse\plugins\com.pemicro.debug.gdbjtag.pne_1.1.8.20141
1191655\win32\pegdbserver_console.exe -startserver -device=KL25Z128M4

P&E GDB Server, Version 5.13.02.00
Copyright 2014, P&E Microcomputer Systems Inc, All rights reserved

Loading library C:\Freescale\KDS_2.0.0\eclipse\plugins\com.pemicro.debug.gdbjtag
.pne_1.1.8.201411191655\win32\gdi\unit_ngs_arm_internal.dll ... Done.

Command line arguments: -startserver -device=KL25Z128M4
Device selected is kl25z128m4
HW Auto-Selected : Interface=OPENSDA Port=DBA07E44   ; USB1 : OpenSDA (DBA07E44)

Connecting to target.
OpenSDA detected - Flash Version 1.14

Device is KL25Z128M4.

Mode is In-Circuit Debug.

'Kinetis' is a registered trademark of Freescale.

(C)opyright 2012, P&E Microcomputer Systems, Inc. (www.pemicro.com)
API version is 101

Server running on 127.0.0.1:7224

With this the server is running and waiting on port 7224 for a connection from the GDB client.

To connect to the P&E GDB server, use this in the gdb client:

target remote localhost:7224

Some monitor commands are documented here: http://www.pemicro.com/forums/forum.cfm?forum_topic_id=3990

💡 I have not found a formal document (yet?) about the P&E monitor commands supported. A tip is to look in the Eclipse debug console view for hints 🙂

_reset           ; Reset the MCU
_r0   ...  _r15  ; Change CPU register Value (param : longvalue)
_fill.w          ;Fill memory words (params : startaddr endaddr wordvalue)
_fill.l          ;Fill memory longwords (params : startaddr endaddr longwordvalue)
_pc              ;Set program counter (param: longvalue)

So to reset the microcontroller, use

monitor _reset

Then I can use the load and file commands to load my application for debug:

Below is the log of a debug session with P&E GDB Server using the ARM GDB client:

Segger GDB Server

There is a GDB server from Segger available from https://www.segger.com/jlink-gdb-server.html. Alternatively, a Segger GDB server is included in the Freescale Kinetis Design Studio (KDS) (https://www.freescale.com/kds). Segger has a GUI version (on Windows only, as far as I know) and a console/command line version. I’m using the command line version here.

The Segger GDB server is named JLinkGDBServerCL.exe and located in the C:\Freescale\KDS_2.0.0\segger folder.

Start it with

JLinkGDBServerCL.exe

The Segger GDB server expects a connection on port 2331. In the GDB client, I use

target remote localhost:2331

With

monitor reset

I can reset the target from the GDB client.

💡 Documentation will commands can be found here: https://www.segger.com/admin/uploads/productDocs/UM08005_JLinkGDBServer.pdf

Next, I select the device to be used:

monitor device = MKL25Z128xxx4

Then I can use the load and file commands to load my application for debug:

Below is the log of a debug session with Segger GDB Server using the ARM GDB client:

GDB Client Commands to Load/Program the Device

The following commands in the gdb client are generic for both P&E and Segger.

Load the application code with the load command:

load c:/tmp/KL25Z_blue.elf

Use the file command to load debug symbols in gdb:

file c:/tmp/KL25Z_blue.elf

Use the continue command to start/continue execution:

continue

With CTRL+C I can stop execution.

With the quit command I terminate the gdb session:

quit

💡 There are plenty of tips and trick for GDB available, see as well http://haifux.org/lectures/222/GDB_haifux_David_Khosid.pdf. For example you can put default commands into a .gdbinit file. Have as well a look https://sourceware.org/gdb/current/onlinedocs/gdb/ for a list of gdb commands.

Automation

Now if it is about to flash/program a bunch of boards, it is much easier to do this from a script, batch or command file. For example I create a text file with the following content:

# Segger: listen on port
target remote localhost:2331

# Segger: reset device
monitor reset

# Segger: specify flash of device
monitor device = MKL25Z128xxx4 

# load/flash application file
load c:/tmp/KL25Z_green.elf

# exit gdb
quit

Now with the GDB server running, I can launch the gdb client with the -x option, passing that command file to it:

💡 GDB uses a similar file named .gdbinit (if it exists) to be executed at gdb startup. So that would be a good place for common settings.

arm-none-eabi-gdb.exe -x gdb_flash.txt

That way it will flash my binary file to the board:

Be free to write your own script: that way you can add the download to your make file or anything else which uses a command line interface.

Summary

GDB comes with a nice command line interface, so no GUI or IDE is needed for debugging or just downloading/flashing an image to a device. The GNU tools come with a generic GDB client which needs to talk to a GDB server, which can be from P&E, Segger or something else like OpenOCD. The commands supported in the server differ from one GDB server to another. With little work, it is possible to setup a command line environment for programming and debugging which is very useful for automated testing or automation in general.

Happy Serving 🙂

Links:

• GDB commands: https://sourceware.org/gdb/current/onlinedocs/gdb/
• Segger GDB Server and Documentation: https://www.segger.com/jlink-gdb-server.html
• PE Micro GDB Server: http://www.pemicro.com/products/product_viewDetails.cfm?product_id=15320151
• Freescale Kinetis Design Studio download: https://www.freescale.com/kds
• Command line debugging with gdb: http://www.chemie.fu-berlin.de/chemnet/use/info/gdb/gdb_3.html and http://www.chemie.fu-berlin.de/chemnet/use/info/gdb/gdb_16.html#SEC143