avr-rust/Lobby

Carl Peto

@carlos4242

agreed... otherwise there's nowhere for me to put bugs...

Or for Ayke to record them if they are just affecting the TinyGo frontend.

oh actually... https://bugs.llvm.org/enter_bug.cgi that's probably good enough?

Jake Goulding

@shepmaster

yeah, ideally with the reduced Rust/Swift/Go and the corresponding reduced LLVM IR

Carl Peto

@carlos4242

True. It’s quite buggy. The thing I like is you are the only people I have on gitter. When I get a message on gitter I know it’s AVR rust related, focused and not “chatter”! :)

Wojciech Niedźwiedź

@Niedzwiedzw

hey

so I can use standard rust and compile for say arduino from now on?

Wojciech Niedźwiedź

@Niedzwiedzw

how do I load it onto the board? :D I have arduino uno

Wojciech Niedźwiedź

@Niedzwiedzw

yeah, I did it!!

https://github.com/Niedzwiedzw/blink great job guys

such satisfaction :D

Carl Peto

@carlos4242

Should be a lot less niche now. We’ll see if a lot of folks get into it. Maybe you can post a video of you getting blink working. Like a simple howto. And tweet it to spread the word?

Jake Goulding

@shepmaster

@dylanmckay I finally remembered what the last fix i needed to get futures running — https://reviews.llvm.org/D82536

As the function pointer relocation of the executor vtable isn't correct

Jake Goulding

@shepmaster

For those who haven’t seen it https://book.avr-rust.com/

Ben Schattinger

@lights0123

I have UART and SPI working with async/await: https://github.com/lights0123/async-avr

I'll have a blog post about it published in a little while, but that runs on yesterday's nightly just fine

Ayke

@aykevl

Unfortunately, https://reviews.llvm.org/D82536 is invalid. I've abandoned it to indicate the current state. However, it may be good enough for you when you replace STT_NOTYPE with STT_FUNC.

Ben Schattinger

@lights0123

https://lights0123.com/blog/2020/07/25/async-await-for-avr-with-rust/

Plecra

@Plecra

Has anyone managed to get the https://book.avr-rust.com/002.1-installing-required-third-party-tools.html running on WSL?

Jake Goulding

@shepmaster

@lights0123 how are you avoiding the LLVM error that @aykevl and I are talking about? It makes the function pointers in the vtable incorrect.

Jake Goulding

@shepmaster

See my code here https://github.com/shepmaster/rust-arduino-blink-led-no-core-with-cargo/blob/master/src/main.rs

Jake Goulding

@shepmaster

@Plecra what problem (s) are you experiencing?

Plecra

@Plecra

I haven't tried it yet ^^ I was following the Rust-AVR book, and it doesn't have any instructions for using the toolchain on windows

I thought someone might've already given it a shot, and it'd be nice to hear how that went

Ayke

@aykevl

@Plecra WSL is basically just Linux, so any instructions for Linux should work

(there might be some exceptions around external devices)

Ben Schattinger

@lights0123

@shepmaster I just... don't? This works just fine for me:

#[export_name = "__vector_18"]
pub unsafe extern "avr-interrupt" fn __vector_18() {
    let mut led: atmega328p_hal::port::portb::PB5<Output> = unsafe { core::mem::zeroed() };
    led.set_high();
}

Ayke

@aykevl

@lights0123 it's possible the compiler managed to optimize away the indirection, this can happen especially when the program is very small

Compilers try to eliminate function pointer calls as function pointers are really hard to optimize.

Ben Schattinger

@lights0123

This works too

#[export_name = "__vector_18"]
pub unsafe extern "avr-interrupt" fn __vector_18() {
    test();
}

#[inline(never)]
fn test() {
    let mut led: atmega328p_hal::port::portb::PB5<Output> = unsafe { core::mem::zeroed() };
    led.set_high();
}

but I don't know how much it actually respects #[inline(never)]

Ayke

@aykevl

The set_high can still be inlined, for example

(I don't really know Rust but I'm assuming it works similar to C here)

Ben Schattinger

@lights0123

yeah but wouldn't that function boundary of test produce the same error?

Ayke

@aykevl

no, that's a direct call

Ben Schattinger

@lights0123

it's a call within a call?

Ayke

@aykevl

an indirect call is a function pointer, whenever you're storing a reference to a function and calling it elsewhere

closures are also a kind of function pointer (not sure whether Rust has them tbh)

Ben Schattinger

@lights0123

yeah it does have closures

Ok, I get it now—is there a problem with the VTable for Futures? I've totally skipped over Wakers for now and am just busy-loop polling.

Ayke

@aykevl

That's a bit out of my Rust knowledge, but normally a vtable is basically an array of function pointers that is usually stored as a global (for virtual functions in C++ for example). Calling a method from a vtable means doing an indirect call (as you're not directly calling the function, but loading the function address from the vtable and calling the function through that).

Again, the compiler will try to optimize the vtable away if possible, which may definitely happen in small programs

You could try looking at the disassembly, if you have any experience with that.

Ben Schattinger

@lights0123

Yep, I just ran into the same problem. When trying to clone a Waker, which calls a function defined in a manual VTable, my Arduino just crashes and doesn't respond.

Jake Goulding

@shepmaster

Yup. That’s because the relocation is invalid and you are jumping to the wrong place.

@aykevl maybe you could ping @dylanmckay for tips on where to look to emit the right assembly?

Jonah Dahlquist

@jonahbron

Hey I just saw that AVR-Rust has been upstreamed, super exciting!

I'm having trouble building though, issues with avr-gcc.

It seems like there avr-gcc flags being set that aren't supported by the one I have installed. Any ideas how to configure how avr-gcc gets called?

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