Change Log

All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog and this project adheres to Semantic Versioning.

Cargo Workspaces

#1011 Add a Cargo.lock to the root workspace to support reproducible binary crate builds such as defmt-print. Resolves [#1000]

Packages

We have several packages which live in this repository. Changes are tracked separately.

defmt
defmt-macros
defmt-print
defmt-decoder
defmt-parser
defmt-rtt
defmt-itm
defmt-semihosting
panic-probe
defmt-test
defmt-test-macros
defmt-json-schema
qemu-run
defmt-elf2table
defmt-logger

defmt

A highly efficient logging framework that targets resource-constrained devices, like microcontrollers

defmt-next

#974 Ensure typechecking is still performed on disabled log statement.
#960 Fix Format not accepting multiple helper attribute instances
#937 add support for #[defmt(transparent)] on Format derive
#959 Missing "unstable-test" cfg in tests module
#956 Link LICENSE-* in the crate folder
#955 Allow using the defmt/alloc feature on bare metal ESP32-S2
#972 Fix logic bug in env_filter
#1007 defmt: impl Format for core::fmt::Error
#983 Add Format implementation for core::num::Wrapping<T>
#1022 Re-fix accidental breaking change in Format macro
#1041 Ignore RUSTSEC-2026-0009
#1052 Pin UI tests to host MSRV

defmt-v1.0.1 (2025-04-01)

#954 Fix accidental breaking change in Format macro

defmt-v1.0.0 (2025-04-01)

#909 First 1.0 stable release 🎉
#940 defmt-print: Allow reading from a serial port
#938 Emit option_env!("DEFMT_LOG") so rustc depinfo can track it
#935 Add note in book's setup chapter to clarify staticlib setup
#914 Add cargo-deny as a CI action to check crate security and licensing

defmt-v0.3.100 (2025-04-01)

#909 Re-exports defmt-1.0.0

defmt-v0.3.10 (2024-11-29)

#902 Minor change to Format impl for core::panic::PanicInfo, eliding a lifetime specifier to satisfy Clippy 1.83.
#899 Pin the defmt-macro crate to avoid incompatible versions being used together

defmt-v0.3.9 (2024-11-27)

#889 Add script for book hosting
#887 Fix interning example in the book
#884 Upgrade dependencies: notify is now at v7, thiserror is now at v2
#883 Mark decoder and parser not as unstable anymore
#880 Merge function calls emitted by the macro to save space.
#874 defmt: Fix doc test
#872 defmt: Add expect! as alias for unwrap! for discoverability
#871 Set MSRV to Rust 1.76
#869 macros: Add missing type hints
#865 defmt: Replace proc-macro-error with proc-macro-error2
#858 defmt: Implement "passthrough" trait impls for *2Format wrappers
#857 Add an octal display hint (:o)
#856 defmt: Add a Format impl for PanicInfo and related types.
#852 CI: Update mdbook to v0.4.40
#848 decoder: add optional one-line format
#847 decoder: Fix log format width specifier not working as expected
#845 decoder: fix println!() records being printed with formatting
#843 defmt: Sort IDs of log msgs by severity to allow runtime filtering by severity
#822 CI: Run cargo semver-checks on every PR

defmt-v0.3.8 (2024-05-17)

#840 defmt: Support pre-1.77
#839 CI: Fix tests
#838 defmt: Switch to Cargo instruction compatible with older versions of Cargo

defmt-v0.3.7 (2024-05-13 (yanked))

#831 CI: Fix CI
#830 book: Add section about feature-gated derive Format
#821 Clean up
#813 doc: add note for the alloc feature flag
#812 defmt: Add a feature to stop linking a default panic handler
#811 book: Add some examples for byte slice/array hints as well
#805 defmt: Drop ip_in_core feature and re-enable nightly snapshot tests

defmt-v0.3.6 (2024-02-05)

#804 CI: Remove mdbook strategy
#803 CI: Disable nightly qemu-snapshot tests
#789 defmt: Add support for new time-related display hints

defmt-v0.3.5 (2023-06-19)

#758 defmt-print: Tidy up
#757 defmt-print: Allow reading from a tcp port
#756 CI: Switch from bors to merge queue
#753 demft Add Format impls for core::ptr::NonNull and fn(Args...) -> Ret (up to 12 arguments)

defmt-v0.3.4 (2023-04-05)

#747 Bump wire version

defmt-v0.3.3 (2023-03-29 (yanked))

#744 defmt-parser: Clean and simplify
#743 defmt-parser: Simplify tests with rstest
#740 Snapshot tests for core::net
#739 xtask: Clean up
#737 panic-probe: Add hard_fault() for use in defmt::panic_handler
#733 defmt: Add formatting for core::net with the ip_in_core feature
#603 defmt: Raw pointers now print as 0x1234 instead of 1234
#536 defmt-parser: Switch to using an enum for errors, and add some help text pointing you to the defmt docs if you use the wrong type specifier in a format string.

defmt-v0.3.2 (2022-05-31)

#669 Refine docs for --json flag

defmt-v0.3.1 (2022-03-10)

Added

#662 #[derive(Format)] now accepts attribute fields to format fields using the Debug2Format adapter instead of a Format implementation.
#661 Add tests for Cell types
#656 Implement defmt::Format for Cell and RefCell
#630 Add test instructions to README.md

Changed

#659 mark extern::acquire() and extern::release() as unsafe. this is not a breaking change; this is an internal API
#640 use crate critical-section in defmt-rtt
#634 update ELF parsing dependencies
#633 make RTT buffer size configurable
#626 Make errror message more meaningful in case of version-mismatch

defmt-v0.3.0 (2021-11-09)

#618 Support #[ignore] attribute in defmt_test
#621 Readme Diagram: Replace duplicate defmt-itm with defmt-rtt
#617 Add display hint to output u64 as ISO8601 time
#620 Tidy up: remove unused code and dependencies
#619 Update all crates to rust edition 2021! 🎉
#610 defmt-print: Log if malformed frame gets skipped
#547 Migration guide v0.2.x to v0.3.0
#604 defmt-test: #[cfg(test)] the #[defmt_test::tests] module
#616 Update user guide part of the book
#615 Document how to deal with backward compatibility breakage
#614 Bugfix: decoder breaks with pipe symbol
#605 Properly handle the off pseudo-level in presence of nested logging directives
#611 Fix cargo doc-warnings
#608 decoder: Fix that defmt::println! shows leading space when timestamps are disabled
#601 Move crate defmt to defmt/
#600 Run snapshot & backcompat tests in dev mode only
#519 Target-side env_logger-like env filter
#592 xtask: add backward compability test
#598 defmt-print: Recover from decoding-errors
#569 Add defmt println! macro
#580 Structure defmt::export
#594 panic-probe: use UDF instruction on nested panics
#591 Remove timestamps from snapshot test
#585 Add xtask option to run a single snapshot test by name
#589 Implement Format for arrays of any length
#587 Tweak inline attributes to remove machine code duplication
#574 Refactor rtt [1/2]
#584 Remove outdated doc "you may only call write! once"
#581 Add impl for alloc::Layout
#579 defmt-rtt: fix check for blocking RTT
#577 Fix typo in cfg of encoding-feature-compile_error!
#578 qemu: Allow dead code
#550 Added defmt::flush()
#570 Support referring to Self in bitflags constants
#568 Encoding docs.
#564 Make order of bitflags values deterministic
#561 Remove unused cortex-m-rt in panic-probe a=Dirbaio
#562 Remove call to fill in user survey from README
#560 Update cortex-m-rt crate from 0.6 to 0.7
#557 Add impl for TryFromSliceError
#556 Add impl for TryFromIntError
#551 Display git version & date to introduction section
#540 Separate "crate version" from "wire format version
#545 Revert "build.rs: Obtain version from macro; simplify"
#539 Add optional rzCOBS encoding+framing
#518 build.rs: Obtain version from macro; simplify
#543 CI: Temporarily drop backward-compatibility check
#542 snapshot-tests: Test alternate hint for bitfields
#538 Fix wrong bit count in comment.
#537 snapshot-tests: Delete :? hint without impact
#531 refactor the macros crate
#534 Attribute test progress message to the test in question;
#535 Don't print leading space when timestamp is absent
#529 Refactor user-guide of book
#528 Support bitflags
#533 Adds add for user survey into readme.
#527 book: Add logo and support text to introduction
#526 decoder: Simplify tests
#359 Implement precedence of inner display hint
#523 Minimize dependencies
#508 [5/n] Format trait v2
#522 Replace µs hint with us
#521 [3/n] Remove u24
#516 xtask: Only install additional targets for tests that require them
#512 Add overwrite option for xtask cross results.
#514 extend raw pointer implementation to include !Format types
#513 book/duplicates.md: discriminator -> disambiguator
#507 [2/n] - Remove code-size-costly optimizations
#505 [1/n] - Logger trait v2.

defmt-v0.2.3 (2021-06-17)

Added

#499 Illustrate structure of the defmt crates
#503 Add alternate hint ('#')
#509 impl Format for NonZero*

Changed

#488 Structure impl Formats into multiple files
#496 Bump build-dep semver to 1.0
#489 Structure lib
#500 book: fix leftover old formatting syntax; typos
#510 CI: Don't install MacOS dependency which is included by default

Fixed

#497 macros: match unused vars if logging is disabled

defmt-v0.2.2 (2021-05-20)

Added

#446 Add usage examples for Debug2Format, Display2Format
#464 impl<T> Format for {*const, *mut} T where T: Format + ?Sized
#472 impl Format for the core::{iter, ops, slice} structs
#473 impl Format for all the Cows
#478 add dbg! macro

Changed

#477 Disable logging calls via conditional compilation when all defmt features are disabled

defmt-v0.2.1 (2021-03-08)

Added

#403 Add knurling logo to API docs

Fixed

#413 Fix docs-rs build, by disabling feature "unstable-test"
#427 Drop outdated note about defmt v0.2.0 from book

defmt-v0.2.0 (2021-02-19)

Added

#284 Implement support for i128 and u128 types
#291 Allows using defmt on x86 platforms by making the test suite use an internal Cargo feature
#293 Make defmt attributes forward input attributes
#294 Permits use items inside #[defmt_test::tests] modules
#296 Allows skipping the defmt version check in order to make development easier
#302 derive(Format) now supports more than 256 variants
#304 impl Format for chars
#313 Add display hints
#323 Merge Uxx(u64) (Ixx(i64)) and U128(u128) (u128(i128)) data variants
#327 impl<T> Format for PhantomData<T>
#329 Document safety of implementation detail functions
#335 Add the defmt-itm crate
#338 Add defmt-logger and defmt-print crates
#343 Customizable timestamps
#347 Document the grammar of defmts current format parameter syntax
#351 Allow tools to distinguish user-controlled format strings from generated ones
#354 Add f64 support
#376 Make defmt-logger more configurable, remove probe-run strings
#377 defmt-test: support returning Result from tests
#382 impl Format for Infallible
#391 impl Format for core::time::Duration

Changed

#297 Improves the output formatting and includes a progress indicator
#299 Test embedded test runner (defmt-test) as part of our CI setup
#300 #[derive] now uses built-in primitive formatting for primitive references
#303 Employ the help of [bors]
#305 Formatter is now passed by value, i.e. consumed during formatting
#308 compile-fail test new Formatter move semantics
#312 str fields in structs are now treated as a native type by the encoder instead of going through the Format trait
#325 Update our UI tests to work with the latest stable release
#331 Add more compile-fail tests
#332 Improve Format trait docs
#333 Hide Formatter's inner field
#334 Fix dead link in parser docs
#337 Improve diagnostics on double write!
#339 Make leb64 encoding fully safe (while at the same time reducing its code footprint)
#340 Stream core::fmt adapters
#345 Reduce code size by avoiding 64-bit arithmetic in LEB encoding
#350 panic-probe now uses defmts Display2Format to log panic messages. In consequence, panic messages won't get truncated anymore.
#355 Clarify the docs on Write::write
#352 Do not display full version with --help. Thanks to [Javier-varez]!
#354 Support f64 floating point numbers.
#355 Clarify docs on Write::write.
#363 Improve test coverage on basic defmt usage on std rust
#364 Split firmware code into separate workspace
#368 defmt-itm: Raise compile error on armv6m
#369 Move bors.toml to .github/
#371 Link to git version of defmt book
#372 Update Printers section in defmt book
#373 Improve information in Cargo.toml
#379 Make link to defmt book clickable
#380 Merge crates elf2table and logger into decoder
#383 defmt-test: Modify attributes in place and handle #[cfg]
#384 pin unstable path dependencies
#385 defmt_decoder: Skip allocation of datastructure for raw symbols of the table entries in fn get_locations
#386, #392 Refactor decoder
- rename mod logger to log
- make fn parse_*, fn get_locations, fn decode methods of struct Table
- various simplifications and restructuring of internal code
#387 CI: bump timeout to 20 minutes
#389 defmt_decoder: Bump deps object and gimli

Fixed

#301 Fix the nightly builds after a linked_list_allocator feature change
#310, #311 remove the runtime check (and matching tests) if the write! macro was called multiple times as this can no longer happen since write! now consumes the Formatter due to #305.
#321 ASCII hint (:a) is now respected when used together with the Format trait (=? and =[?]).
#342 Fix a data corruption issue when using bools in write!
#357 Fix issue preventing defmt from compiling on MacOS.

defmt-v0.1.3 (2020-11-30)

Fixed

#290 fixed cross compilation to ARMv6-M and other targets that have no CAS (Compare-and-Swap) primitives when the "alloc" feature is enabled

defmt-v0.1.2 (2020-11-26)

Added

#263 #276 add and document write! macro
#273 #280 add and document unwrap! macro
#266 add panic!-like and assert!-like macros which will log the panic message using defmt and then call core::panic! (by default)
#267, #281 add Debug2Format and Display2Format adapters
#279 started adding notes about feature availability (e.g. "defmt 0.1.2 and up")

Changed

#257 code size optimizations
#265 updated the 'how we deal with duplicated format strings' section of our implementation notes

Fixed

#264 probe-run doesn't panic if log message is not UTF-8
#269 fixes compiler error that was thrown when using defmt::panic within e.g. a match expression
#272 braces in format args passed to the new defmt::panic! and defmt::assert! macros do not cause unexpected errors anymore

defmt-v0.1.1 (2020-11-16)

Fixed

#259 crates.io version of defmt crates no longer require git to be built

defmt-v0.1.0 (2020-11-11)

Initial release

defmt-macros

Macros for defmt

defmt-macros-next

#1044: Add support for bound attribute via a #[defmt(bound(T: MyCustomBound))]
#956: Link LICENSE-* in the crate folder

defmt-macros-v1.0.1 (2025-04-01)

#954: Fix accidental breaking change in Format macro

defmt-macros-v1.0.0 (2025-04-01)

#948 Add support for specifying the defmt crate path for the Format derive via a #[defmt(crate = path )] helper attribute
#909 First 1.0 stable release 🎉

defmt-macros-v0.4.0 (2024-11-29)

#899 Just a major version bump to stop it being used by older defmt versions.

defmt-macros-v0.3.10 (2024-11-27)

defmt-macros-v0.3.9 (2024-05-14)

#835 macros: Fix some defmt crate name usage

defmt-macros-v0.3.8 (2024-05-13)

defmt-macros-v0.3.7 (2024-03-05)

defmt-macros-v0.3.6 (2023-08-01)

defmt-macros-v0.3.5 (2023-05-05)

#750 Add support for decoding wire format version 3

defmt-macros-v0.3.4 (2023-03-29)

defmt-macros-v0.3.3 (2022-10-07)

defmt-macros-v0.3.2 (2022-03-10)

defmt-macros-v0.3.1 (2021-11-26)

defmt-macros-v0.3.0 (2021-11-26)

defmt-macros-v0.2.3 (2021-06-21)

defmt-macros-v0.2.2 (2021-06-01)

defmt-macros-v0.2.1 (2021-05-21)

defmt-macros-v0.2.0 (2021-02-19)

defmt-macros-v0.1.1 (2020-11-26)

defmt-macros-v0.1.0 (2020-11-30)

Initial release

defmt-print

A tool that decodes defmt logs and prints them to the console

defmt-print-next

No changes

defmt-print-v1.1.0 (2026-01-20)

#985 Add --set-addr option to actively set the _SEGGER_RTT address
#952 Support sending dtr on connection for serial port input
#965 Also support --log-format=online or --log-format=default
#986 Bump MSRV to 1.81
#1028 Bump MSRV to 1.83

defmt-print-v1.0.0 (2025-04-01)

#909 First 1.0 stable release 🎉

defmt-print-v0.3.13 (2024-11-27)

#807 Add watch_elf flag to allow ELF file reload without restarting defmt-print
#855 defmt-print: Now uses tokio to make tcp and stdin reads async (in preparation for a watch elf flag)

defmt-print-v0.3.12 (2024-05-13)

defmt-print-v0.3.11 (2024-03-05)

defmt-print-v0.3.10 (2023-10-04)

defmt-print-v0.3.9 (2023-08-01)

defmt-print-v0.3.8 (2023-08-01)

defmt-print-v0.3.7 (2023-05-05)

#750 Add support for decoding wire format version 3

defmt-print-v0.3.6 (2023-04-05)

defmt-print-v0.3.5 (2023-03-29)

defmt-print-v0.3.4 (2023-01-24)

#719 defmt-print: Fix panic

defmt-print-v0.3.3 (2022-10-07)

#703 defmt-print: Update to clap 4.0.
#682 defmt-print: exit when stdin is closed

defmt-print-v0.3.2 (2022-03-10)

defmt-print-v0.3.0 (2021-11-10)

defmt-print-v0.2.2 (2021-06-21)

defmt-print-v0.2.1 (2021-05-21)

defmt-print-v0.2.0 (2021-02-19)

[defmt-print-v0.1.0] (2021-01-15)

Initial release

defmt-decoder

Decodes defmt log frames

defmt-decoder-next

defmt-decoder-v1.1.0 (2026-01-20)

#1004 decoder: add Send + Sync bound to returned StreamDecoder
#990 improve version mismatch error message, don't mention probe-run.
#986 Bump MSRV to 1.81
#966 Add Frame::fragments() and Frame::display_fragments()
#958 Update to object 0.36
#1028 Bump MSRV to 1.83
#1036 Impl serde::{Serialize, Deserialize} and Clone on Table and related types

defmt-decoder-v1.0.0 (2025-04-01)

#909 First 1.0 stable release 🎉
#902 Minor change to impl StreamDecoder for Raw and Rzcobs, eliding a lifetime specifier to satisfy Clippy 1.83. No observable change.
#916 Support the ":cbor" display hint, adding new dependency cbor-edn.

defmt-decoder-v0.4.0 (2024-11-27)

defmt-decoder-v0.3.11 (2024-05-13)

defmt-decoder-v0.3.10 (2024-03-05)

defmt-decoder-v0.3.9 (2023-10-04)

defmt-decoder-v0.3.8 (2023-08-01)

defmt-decoder-v0.3.7 (2023-05-05)

defmt-decoder-v0.3.6 (2023-04-05)

defmt-decoder-v0.3.5 (2023-03-29)

defmt-decoder-v0.3.4 (2023-01-24)

#726 Remove difference in favor of dissimilar
#725 Replace chrono with time

defmt-decoder-v0.3.3 (2022-08-09)

#681 Make use of i/o locking being static since rust 1.61.

defmt-decoder-v0.3.2 (2022-03-10)

defmt-decoder-v0.3.1 (2021-11-26)

defmt-decoder-v0.3.0 (2021-11-10)

defmt-decoder-v0.2.2 (2021-06-21)

defmt-decoder-v0.2.1 (2021-05-21)

defmt-decoder-v0.2.0 (2021-02-19)

defmt-decoder-v0.1.4 (2020-11-26)

defmt-decoder-v0.1.3 (2020-11-30)

defmt-decoder-v0.1.0 (2020-11-30)

Initial release

defmt-parser

Parsing library for defmt format strings

defmt-parser-next

#956 Link LICENSE-* in the crate folder
#1028 Clarify that MSRV is 1.76

defmt-parser-v1.0.0 (2025-04-01)

#916 Mark DisplayHint as non_exhaustive. This is a breaking change.
#916 Add display hint ":cbor", indicating RFC8949 encoded data to be displayed in diagnostic notation.
#909 First 1.0 stable release 🎉

defmt-parser-v0.4.1 (2024-11-27)

#897 Added its own README

defmt-parser-v0.4.0 (2024-11-27)

defmt-parser-v0.3.4 (2024-03-05)

defmt-parser-v0.3.3 (2023-05-05)

defmt-parser-v0.3.2 (2023-03-29)

defmt-parser-v0.3.1 (2022-03-10)

defmt-parser-v0.3.0 (2021-11-10)

defmt-parser-v0.2.2 (2021-06-21)

defmt-parser-v0.2.1 (2021-05-21)

defmt-parser-v0.2.0 (2021-02-19)

defmt-parser-v0.1.0 (2020-11-30)

Initial release

defmt-rtt

Transmit defmt log messages over the RTT (Real-Time Transfer) protocol

defmt-rtt-next

#1006 Fix available_buffer_size ignoring available buffer space when read < write
#1013 Switch to fixed 32-bit types, to support 64-bit targets

defmt-rtt-v1.1.0 (2025-10-09)

#968 Add in_blocking_mode public method

defmt-rtt-v1.0.0 (2025-04-01)

#909 First 1.0 stable release 🎉

defmt-rtt-v0.4.2 (2025-03-27)

#902 Use core::ptr::addr_of_mut! instead of &mut on mutable statics. No observable change.
#901 defmt-rtt: Update to critical-section 1.2
#915 Introduced disable-blocking-mode feature
#949 Re-worked to remove all usage of static mut
#950 Removed some redundant checks from write and flush