RTIC app crate that avoids lto = "thin"?

[psentee]

I'm starting a Teensy4 project, and I want to use RTIC (new shiny 2.0 if it matters), starting with the rtic_usb_log example, and it works – as long as I set release profile to exactly lto = "thin" in my Cargo.toml. With lto = false or lto = true/"fat" it tails to build with Linking globals named 'USB_OTG1': symbol multiply defined!. This happens with both GNU ld and lld.

I found some cryptic comment about default features of teensy4-hal conflicting with rtic and LTO being able to sort it out (in practice, only "thin" LTO). I haven't been able to find any examples of how to set teensy4-rs features to work with rtic, or any features in its Cargo.toml that look like they could do the trick.

I found some historical mentions of patching cortex-m-rt in the app to point at teensy4-rt crate that doesn't exist nowadays. Also, found some mentions of a replacement/patched cortex-m-rt crate that has been removed from this repo in the meantime. I'm confused and have no idea what can I do to make it work other than blindly setting lto = "thin" without understanding what I'm doing and giving up on full LTO.

Any hints?

ETA: my code is here: https://github.com/psentee/teensy4-rs-example – it fails to build with Linking globals named 'USB_OTG1': symbol multiply defined! and after switching to lto = "thin" it builds fine.

[mciantyre]

Sorry for the trouble, and thanks for the example code. Could you give psentee/teensy4-rs-example#1 a test?

The BSP's usb-logging feature provides a convenience for non-RTIC users. When enabled, the BSP defines USB_OTG1. This results in a duplicate definition once an RTIC application also defines USB_OTG1. By disabling usb-logging, we remove the BSP convenience, allowing users to manage USB logging and USB_OTG1 however they want.

Let me know if that works. If it does, I'll make sure to note this in the BSP documentation.

[psentee]

Besides docs, it might be helpful to add a comment in the rtic_usb_log example to explain that this code does not use the usb-logging feature – this part was not obvious to me (the code was doing USB logging, so I assumed it was necessary).

[psentee]

That fixes the problem, thank you! And I forgot to thank you for all the work on imxrt and teensy4 support! I have hacked together a Rust teensy4 project back in 2019, it was an uphill battle and I can only imagine the amount of work that went into the imxrt-rs/teensy4-rs ecosystem.