1 free interrupt (`extern { .. }`) is required to dispatch all soft tasks

[arrowcircle]

Hi! I am new to Rust and maybe asking stupid questions. I am trying to make simple blink with RTFM and stm32f103. This code didn't work before, but compiled fine.

I am trying to use code like this

#![no_std]
#![no_main]

extern crate stm32f1;
extern crate panic_halt;

use rtfm::app;
// use cortex_m_semihosting::hprintln;

#[app(device = stm32f1::stm32f103)]
const APP: () = {

    #[init(schedule = [led])]
    unsafe fn init() {
        hprintln!("Initializint perphs").unwrap();

        let peripherals = stm32f1::stm32f103::Peripherals::take().unwrap();
        let gpioc = &peripherals.GPIOC;
        let rcc = &peripherals.RCC;

        // enable the GPIO clock for IO port C
        hprintln!("Enabling GPIO").unwrap();
        rcc.apb2enr.write(|w| w.iopcen().set_bit());
        gpioc.crh.write(|w| {
            w.mode13().bits(0b11);
            w.cnf13().bits(0b00)
        });

        hprintln!("Starting loop").unwrap();

        schedule.led(Instant::now() + 2_000_000.cycles()).unwrap();
    }

    #[task(schedule = [led])]
    unsafe fn led() {
        hprintln!("Toggling LED").unwrap();
        gpioc.bsrr.write(|w| w.bs13().set_bit());
        cortex_m::asm::delay(2000000);
        gpioc.brr.write(|w| w.br13().set_bit());
        cortex_m::asm::delay(2000000);
        let now = Instant::now();
        schedule.led(now + 2_000_000.cycles()).unwrap();
    }
    extern "C" {
    }
};

Today I've done rustup update and now I get compilation error:

cargo build
   Compiling air v0.1.0 (/Users/ionbuggy/projects/rust/air)
error: 1 free interrupt (`extern { .. }`) is required to dispatch all soft tasks
  --> src/main.rs:10:1
   |
10 | #[app(device = stm32f1::stm32f103)]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

error: Could not compile `air`.

To learn more, run the command again with --verbose.

How should I fix this problem (and read about it more)? Or maybe there are some working blink examples with recent version of rtfm and stm32?

[knoby]

You are missing an interrupt to dispatch your task.
Try to add one interrupt from your hardware to the extern C block.

Also have a look at the documentation about tasks:

https://japaric.github.io/cortex-m-rtfm/book/en/by-example/tasks.html

[arrowcircle]

Thanks. What is general safe interrupt to use?

Now I have different error:

cargo build
   Compiling air v0.1.0 (/Users/ionbuggy/projects/rust/air)
error[E0425]: cannot find value `gpioc` in this scope
  --> src/main.rs:38:9
   |
38 |         gpioc.bsrr.write(|w| w.bs13().set_bit());
   |         ^^^^^ not found in this scope

error[E0425]: cannot find value `gpioc` in this scope
  --> src/main.rs:40:9
   |
40 |         gpioc.brr.write(|w| w.br13().set_bit());
   |         ^^^^^ not found in this scope

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0425`.
error: Could not compile `air`.

To learn more, run the command again with --verbose.

This code works ok without rtfm, but does not work with it. Any ideas?

[knoby]

Hey,

Regarding the question with the interrupts the answer is simple: use an interrupt that is not used in your application.

Your compilation problem is a little bit complicated. The complier does not know gpioc because you declared it in the init function and after that it is dropped.

Also I think your code will panic on the device because rt takes the peripherals.
Details can be found in the doc about the init function:
https://japaric.github.io/cortex-m-rtfm/book/en/by-example/app.html?highlight=Device#init

In your example you are modifying the registers by hand, so you can easily mess it up. I think it is a good idea to use a Hal crate for your device.

I did a similar example with the same device and a Hal crate: https://github.com/knoby/rustocopter/blob/012b12bb31aabd7b291d84544bb80e29f1e63c4c/src/main.rs

Here is some information about the idea of the embedded eco system: http://blog.japaric.io/brave-new-io/

[knoby]

There was a workshop about rtfm on the oxidize conf this year:

https://github.com/korken89/rtfm_workshop

[arrowcircle]

THanks for the answers. Thing is, that I am using this crate https://github.com/stm32-rs/stm32-rs because it support CAN bus for stm32. All other examples are using other crate without CAN bus support.