Embedded Rust Basics.

There is a lot to learn, so let’s start simple.

1. Connect the board to your computer and access the first project:

   cd exercises/hello_world
   

2. Build, flash, and monitor the project with cargo run. You should see:

   ..
   0x4080082e - handle_interrupts
   at ??:??
   ..
   Commands:
       CTRL+R    Reset chip
       CTRL+C    Exit
   ..
   loop..!
   ..
   

   We will talk about the at ??:?? in the next chapter about panic!.

   The loop..! logs come from esp-println. They provide us with dbg!, print! and println!.

Build, flash and monitor?

The .cargo/config.toml includes this config:

[target.riscv32imac-unknown-none-elf] # our processor arch.
runner = "espflash flash --monitor"   # for `cargo run`.

Our cargo run is replaced by cargo build && espflash flash <elf_path> --monitor.

Note

This builds and flashes the binary. Then monitors for any logs. Without the --monitor it flashes and exits instead of waiting and printing logs.

Exercise

esp-println supports backends log and defmt which provide info!, warn! other macros. Let’s try adding them:

1. Uncomment the lines in src/main.rs and in Cargo.toml to enable log.
2. The log crate logging level is controlled with ESP_LOG under the [env] section in .cargo/config.toml.

   • Change the ESP_LOG variable to turn off all logs. Re-run cargo run --release, to test how it works.

   • Try with other levels, for example, with trace.

The exercises/hello_world/examples/hello_world.rs contains a solution.

You can run it with the following command cargo run --release --example hello_world. You should first fix the lines at the bottom of Cargo.toml.

Suggested Reading

• esp-println
• log this one you can just peek at to have a general idea.