Wasm on ESP32-C3

This is a demonstration of running a WebAssembly interpreter (in this case wasmi) on the ESP32-C3 RISC-V Microcontroller. This is a very basic demonstration, where the runtime only provides a few functions to call from WebAssembly. A usage of the API is shown in the languages C, C++ and Rust. The runtime's functionality includes reading and writing to GPIOs and communication over a UART connection.

This demo is build upon Espressifs effort of porting the Rust standard library to their boards, running on the esp-idf development framework. In order to run the demonstration you would need to use the latest Rust nightly compiler. Further Instructions can be found under setup.

How this demo works

The compiled WASM application code will be flashed onto the board as part of a static variable in the Rust code (found in src/bytes.rs). At runtime these bytes will be loaded and executed. To show an example usage, this demo involves three subprojects in C, C++ and Rust, which all include a small abstraction of the runtimes API and a program that basically implements the following example control flow:

PROGRAM example_usage:
    pin_8 = Pin 8 (LED) as output
    pin_10 = Pin 10 as input

    uart = uart over pins 2 (rx) and 3 (tx)

    LOOP:
        pin_8.set_high()

        value_10 = pin_10.is_high()
        if value_10 then
            msg = "value 10 is hi"
        else
            msg = "value 10 is lo"
        end if

        print(msg)
        uart.write(msg)

        sleep(1 second)

        pin_8.set_low()
        sleep(1 second)
    end LOOP
end PROGRAM

Each executable contains a start functions that implements the above behaviour. When loaded, the runtime needs to resolve each API call. This is done via the Runtime struct defined in src/runtime.rs. The runtime object also holds information about the current state of the program, like opened UART connections and initialized Gpios.

Setup

If you don't have rustup installed yet, follow the instructions on the rustup.rs site. Then install the nightly Rust compiler toolchain via:

rustup install nightly
rustup component add rust-src --toolchain nightly

To build this project you also need a recent Clang compiler, the Clang getting started website explains the available install options.

It is also necessary to install the following cargo subcommands...

cargo install ldproxy # linker proxy, used by this project
cargo install espflash # for flashing the binary onto the board
cargo install espmonitor # for monitoring the system state and accessing stdout

... and the platform.io core package. Installation instructions can be found here.

After a succsefull installation of the tools you are ready to build the project:

cargo build --release

Then flash the binary with the following command:

espflash /dev/ttyUSB0 target/riscv32imc-esp-espidf/release/wasm-on-esp32c3

• Replace /dev/ttyUSB0 with the USB port where you've connected the board

Then monitor the app via:

espmonitor /dev/ttyUSB0

To build each application, follow the specific instructions.