Logging

Ariel OS supports logging on all platforms and it is enabled by default with the logging-facade laze module. Logging offers a set of macros that print on the debug console with helpful logging formatting.

Logging

Within Rust code, import ariel_os::log items, then use Ariel OS logging macros:

use ariel_os::log::info;

#[ariel_os::task(autostart)]
async fn main() {
    info!("Hello!");
}

Filtering Logs

In Ariel OS, the log level defaults to info. It can be configured using the laze variable LOG. Depending on the logger, it may be possible to configure different levels per crate or per module.

Example:

$ laze build -C examples/log --builders nrf52840dk -DLOG=info run

Logging Facades and Loggers

Ariel OS supports multiple logging facades and loggers. Only one of them may be enabled at a time; if none of them are enabled, logging statements become no-operations. Enabling either the defmt or log laze modules allows selecting which logging facade and logger is used. defmt should be preferred when possible as it results in smaller binaries.

Tip

The defmt laze module is favored and enabled by default when possible for the target. Applications that specifically depend on it still need to explicitly select it to make the dependency explicit and increase robustness to potential future changes.

The precise set of formatting operations and traits required on formatted data depends on the selected backend. There are some wrapper structs available in the ariel_os::log module that help represent some types in a portable way; in particular, this includes Debug2Format and Display2Format, which (while defeating some of defmt’s optimizations) come in handy when debugging third party types.

defmt

See the defmt documentation for general info on the defmt’s facade and logger.

The defmt logger supports configuring the log level per crate and per module, as follows:

$ laze build -C examples/log --builders nrf52840dk -DLOG=info,ariel_os_rt=trace run

Note: On Cortex-M devices, the order of ariel_os::log::println!() output and defmt log output is not deterministic.

log

Ariel OS’s logger for log supports configuring the log level globally, but does not currently support per-crate filtering.