`global_logger` + printer for non-realtime logging?

[twitchyliquid64]

Afaict all the existing global loggers assume you are one with the uC via RTT or semihosting or similar. Are you aware of any logger, or plans for one, that would support yeeting the log frames into memory / SD card, and then decoding them later?

[twitchyliquid64]

One potential challenge: with probe run or similar its quite impossible to decode the log frames against the wrong ELF, but thats definitely an easy mistake to make when copying around files. Is there any kind of 'unique marker' or similar that gets written to the log frames at the beginning, and is also present in the ELF?

[MathiasKoch]

I have created this to eventually be used at my workplace: https://github.com/BlackbirdHQ/defmt-persist

I would be happy to see it gain some OS adoption, and are more than happy to take contributions.

It is still a WIP, and currently hangs a bit on a few blockers, main ones being:

• embedded-storage repo (in progress: Storage Traits for on and off board storage rust-embedded/embedded-hal#241 (comment))
• Framing options in defmt (Functions in defmt::Write to allow encoding and framing #185)

Basically I make use of an embedded-storage trait to work as storage space (stack/heap, SD-card, file system, flash storage etc), where i implement a BIP style circular buffer on top, with the first N bytes allocated as header.
I then store each log message with a CRC checksum in a COBS encoded format, making it easy to distinguish frames from each other, and some functions to retreive the log frames afterwards (how you then transfer the frames are up to you. Could be RTT, semihosting, network, etc. In my case I am using MQTT)

I have a small static queue to make sure we can move the long running workload of writing to storage, into some low priority idle function, inspired a bit by cortex-m-funnel.

So basically:

#[global_logger] ---> queue ---> Storage ---> Transport
                              ^ In idle     ^ On request

[twitchyliquid64]

Nice! I've started on a global logger that just puts everything into a circular buffer, with the aim that user-code will service the buffer and send it to the computer via UART. It didnt work however and I need to debug it, so I'm keen to use the queue/buffer bits of defmt-persist instead :)

My current focus is on the formatting hints PR, but let me know if theres anything I can help with I can circle back to and help out!

[MathiasKoch]

Yeah, i already added that to defmt-persist, but i probably should add a few examples...

If you have a look in https://github.com/BlackbirdHQ/defmt-persist/blob/master/src/stack.rs, i have basically implemented the Storage traits needed for defmt-persist on any regular &'static [u8]

I do hope we can push for the storage traits to reach some release, where i don't have to tie the crate to a git dependency

[jonas-schievink]

We have now published defmt-print, a command-line tool that decodes defmt frames from stdin. This should be helpful for custom defmt pipelines, including decoding log frames "post-mortem".

[jonas-schievink]

Given that all pieces you need to implement arbitrary defmt storage and transport solutions are now in place, closing this as fixed.