defmt ("de format", short for "deferred formatting") is a highly efficient logging framework that targets resource-constrained devices, like microcontrollers.
For more details about the framework check the book at https://defmt.ferrous-systems.com.
The git version of the defmt book can be viewed at https://defmt-next.ferrous-systems.com/.
The fastest way to get started with
defmt is to use our app-template to set up a new Cortex-M embedded project.
defmt in your existing project, follow our Application Setup guide.
defmt always compiles on the latest
stable rust release. This is enforced by our CI building and testing against this version.
It still might work on older rust versions, but this isn't ensured.
The following diagram illustrates the user-facing and internal crates of the defmt framework.
Tests are run using
cargo xtask -- although this is simply an alias (defined in
cargo run --package xtask --.
To see a list of options, see
xtask/src/main.rs, or run:
$ cargo xtask help
For example, to run all the tests, run:
$ cargo xtask test-all
You will need
qemu-system-arm installed and in your
$PATH for some of the tests (e.g.
If you think that our work is useful, consider sponsoring it via GitHub Sponsors.
Licensed under either of
at your option.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be licensed as above, without any additional terms or conditions.