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Post Chunks with GDB

In the following tutorial we will walk through how to post chunks directly to the Memfault cloud using the memfault GDB commands included in the memfault-firmware-sdk.

This is typically most helpful as a quick way to test that data collection is working prior to implementing the data transport path.

Prerequisites#

  • You need to have a way to debug your product with GDB as part of your development setup
  • The GDB version you are using needs to have the GDB Python API enabled. (It's generally the default or there is a -py version of GDB which has it included.)
  • You need to compile your firmware with debug symbol information (i.e -g CFLAG)
note

Even if you are using other compilers such as ARMCC or IAR, you can load the ELF (.out, .elf) generated and debug it in GDB as well.

Launch GDB and connect debugger#

For example:

$ arm-none-eabi-gdb-py my_app.elf --ex="target remote :3333"
(gdb)

Load Memfault GDB script#

Copy and paste and run the following in gdb:

python exec('try:\n from urllib2 import urlopen\nexcept:\n from urllib.request import urlopen'); exec(urlopen('https://mflt.io/memfault-gdb-script').read())
tip

Some GDB versions do not support Python scripting by default. If you see a message like "Python scripting is not supported in this copy of GDB", you might be able to run an alternative GDB binary with a -py suffix, for example arm-none-eabi-gdb-py.

Register Handler#

Copy the command below and paste it into GDB and hit enter. This will load a handler which automatically posts data to Memfault whenever memfault_data_export_dump_chunks is called.

memfault install_chunk_handler --verbose --project-key <YOUR_PROJECT_KEY>
note

memfault_data_export_dump_chunks() needs to be called by your port as part of a CLI command or periodic task in order for the data to be extracted. For example:

#include "memfault/components.h"
int export_data_cli_command(int argc, char *argv[]) {
memfault_data_export_dump_chunks();
return 0;
}
void some_periodic_task(void) {
memfault_data_export_dump_chunks();
}

Try It Out!#

Now, every time memfault_data_export_dump_chunks is called, the data passed as a parameter to the function will automatically be posted to the Memfault cloud. You don't have to do anything else! You will see logs print in the gdb CLI as data is posted:

(gdb) Continuing.
Successfully posted 45 bytes of chunk data
Successfully posted 53 bytes of chunk data
[...]