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Updated 003.0 Building a crate for AVR #44

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Updated 003.0 Building a crate for AVR #44

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22 changes: 11 additions & 11 deletions src/003-building-a-crate-for-avr.md
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Expand Up @@ -4,40 +4,40 @@ After setting up the compiler, you may use it to generate assembly or machine co

## Choosing a `--target`

The Rust nightly compiler includes a built-in target for ATmega328 named `avr-unknown-gnu-atmega328`
The Rust nightly compiler includes a built-in target for ATmega328 named `avr-unknown-gnu-atmega328`.

If you wish to target a microcontroller other than ATmega328, or you want to change any of the
default builtin options like the linking parameters, then you will need to export the builtin
default built-in options like the linking parameters, then you will need to export the built-in
`avr-unknown-gnu-atmega328` target to a custom target specification JSON file and modify
it to suit your needs.

This target can be adapted to other microcontrollers as per the instructions in [3.1. The built-in `avr-unknown-gnu-atmega328` target](./003.1-the-avr-unknown-gnu-atmega328-target.md).

In summary, there are two options:

* Use `rustc --target=avr-unknown-gnu-atmega328` to use the default, builtin GCC based target for ATmega328
* Or use `rustc --target=my-custom-avr-target.json` with either a JSON file adapted from the builtin
* Use `rustc --target=avr-unknown-gnu-atmega328` to use the default, built-in GCC based target for ATmega328
* Or use `rustc --target=my-custom-avr-target.json` with either a JSON file adapted from the built-in
`avr-unknown-gnu-atmega328` target above, or otherwise build the file you wish manually to avoid the
default path entirely.

## Make sure you use the nightly version of Rust, not the default stable channel
## Using the right Rust compiler

The best way to ensure a crate is using the Nightly compiler is to run `rustup override set nightly` inside a terminal
within the root directory of the crate. After this is done, `cargo` will by-default use the AVR-enabled Nightly compiler
Make sure you use the `nightly` version of Rust, not the default stable channel.
The best way to ensure a crate is using the `nightly` compiler is to run `rustup override set nightly` inside a terminal
within the root directory of the crate. After this is done, `cargo` will by default use the AVR-enabled Nightly compiler
any time `cargo` is used within the directory tree of the crate.

## Compiling a crate

To compile and link an executable crate for AVR, run the following:
Depending on the option you selected from above, you can compile and link the executable crate for AVR with either of the commands below.

Using the builtin `avr-unknown-gnu-atmega328` target:
If you used the builtin `avr-unknown-gnu-atmega328` target, run:

```bash
cargo build -Z build-std=core --target avr-unknown-gnu-atmega328 --release
```

Using a custom target specification JSON:

If you used a custom target specification JSON, run:

```bash
cargo build -Z build-std=core --target /path/to/my-custom-avr-target.json --release
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