Access peripherals from different modules

[keymusic]

Hi Rust experts and AVR fans,

First of all: Thank you for providing this Rust abstraction layer for the AVR controllers. The examples are very helpful to get started.

For some years I have been using these 8-bit controllers in several applications. I wrote code in Assembler, C, C++ and with the Arduino framework.
The last months I spent some time to learn Rust. I am particularly interested in embedded applications.
I could successfully implement a small application on an Arduino with LEDs, push-buttons and some serial output.
Now, I try to refactor the application and move code to dedicated modules:

• one module for LEDs
• one module for push-buttons
• one module for serial output

The main function should initialize these modules.

I did not manage it to to use different peripherals in different modules.
If I understand it correctly, only one function can take all the peripherals.

let dp = arduino_hal::Peripherals::take().unwrap();
let pins = arduino_hal::pins!(dp);

So, for the serial peripheral I did it similarly as described in #115 where Rahix proposed a solution on 2022-01-28.

In the main code I pass the serial peripheral to my console module:

let serial = arduino_hal::default_serial!(dp, pins, 57600);
console::console::init(serial);

But I get the following messages

warning: Linking globals named 'DEVICE_PERIPHERALS': symbol multiply defined!

error: failed to load bitcode of module "avr_device-f61410d5a9432922.avr_device.2c1c7d05340c00bc-cgu.0.rcgu.o":

Main questions:

1. How can I fix this error?
2. Is it possible at all to move the ownership for certain peripherals to modules in other files?

Further questions:
3. What is the granularity level for peripherals? Can I move the ownership of a certain port or pin to another function or module?
4. Do you have further example code where peripherals are accessed from different modules?

Thanks for any hints.
michaeL

[stappersg]

How can I fix this error?

😄 plus https://duckduckgo.com/?t=ftsa&q=rust++error%3A+failed+to+load+bitcode+of+module&ia=web

Another approach could be providing a "git clone URL" to make reproducing the error possible.

[keymusic]

Thank you, @stappersg, for your prompt suggestions. - Sorry, for my delayed response.

I wrote a simple application which demonstrates my problem. It also appears if the macro for serial console output is implemented in the file where it is used.

Please have a look at https://github.com/keymusic/advent_wreath/blob/linker_error/src/main.rs.

When I call cargo build I get the following messages:

warning: Linking globals named 'DEVICE_PERIPHERALS': symbol multiply defined!
error: failed to load bitcode of module "avr_device-f61410d5a9432922.avr_device.2c1c7d05340c00bc-cgu.0.rcgu.o":
warning: advent_wreath (bin "advent_wreath") generated 1 warning

[Rahix]

Hi,

I think you are running into a very nasty cargo behavior that isn't obvious at all: Looking at your dependencies here:

[dependencies.avr-device]
version = "0.6.0"
features = ["atmega328p"]

[dependencies.arduino-hal]
git = "https://github.com/rahix/avr-hal"
rev = "190f2c3cb8d29e10f71119352b912369dc5a1fb7"
features = ["arduino-uno"]

While you are depending on avr-device=0.6, the version of arduino-hal you are pulling in specifies this:

avr-hal/arduino-hal/Cargo.toml

Lines 54 to 55 in 190f2c3

	[dependencies.avr-device]
	version = "0.5.1"

Cargo now adds both versions of avr-device to your dependency tree to satisfy these requirements. But because avr-device is a low-level crate, it defines things like hardware singletons, as expressed by the DEVICE_PERIPHERALS symbol. Because two versions of avr-device try to define this symbol, you get the error you are observing.

The fix is simple, just depend on avr-device=0.5.1 in your crate as well.

[keymusic]

Hi Rahix,

Thank you very much for your support. Yes, this was the reason. The fix was as simple as you have described.
I think, it would have tanken me a long time to find the cause, if I had found the it at all.
With your explanations, it is totally plausible, why the linker error occurs.

[Rahix]

Regarding your other questions:

Is it possible at all to move the ownership for certain peripherals to modules in other files?

The common pattern is to initialize peripherals in main() and then move them into the respective module struct.

What is the granularity level for peripherals? Can I move the ownership of a certain port or pin to another function or module?

After initializing the Pins struct with the pins!() macro, you can move individual pins to whereever you like.

Do you have further example code where peripherals are accessed from different modules?

Not really, I am afraid. But it shouldn't be too difficult to figure out: Just create structs for each "module" and move the required peripherals into those structs.

[keymusic]

Also thanks for these conceptual explanations.
Maybe I find some time after the Christmas Holidays ("between the years") to play around with this.
Please have a good festive season!