Crate defmt_rtt 

defmt global logger over RTT.

NOTE when using this crate it’s not possible to use (link to) the rtt-target crate

To use this crate, link to it by importing it somewhere in your project.

// src/main.rs or src/bin/my-app.rs
use defmt_rtt as _;

Blocking/Non-blocking

probe-rs puts RTT into blocking-mode, to avoid losing data.

As an effect this implementation may block forever if probe-rs disconnects at runtime. This is because the RTT buffer will fill up and writing will eventually halt the program execution.

defmt::flush would also block forever in that case.

If losing data is not an concern you can disable blocking mode by enabling the feature disable-blocking-mode

Critical section implementation

This crate uses critical-section to ensure only one thread is writing to the buffer at a time. You must import a crate that provides a critical-section implementation suitable for the current target. See the critical-section README for details.

For example, for single-core privileged-mode Cortex-M targets, you can add the following to your Cargo.toml.

[dependencies]
cortex-m = { version = "0.7.6", features = ["critical-section-single-core"]}

With feature drop-on-contention you do not need a critical section implementation and interrupts are not disabled. Instead, when execution contexts collide, frames are dropped. This mode is for bare-metal Cortex-M use where thread mode is a single execution context. It is not correct on RTOS or other multi-thread-mode systems because all thread-mode tasks share IPSR == 0, which can misidentify ownership and panic. It can be combined with disable-blocking-mode, in which case frames that do not already fit are dropped. Because the public write cursor advances only once at frame end, every encoded frame in this mode must fit within the RTT ring’s usable capacity (BUF_SIZE - 1); oversized frames are dropped even in blocking mode.

Functions

in_blocking_mode

Report whether the SEGGER RTT up channel is in blocking mode.