Sample Rust app for Epsilon

This is a sample EADK app for the NumWorks calculator which uses a C "harness" to run a Rust application.

Why?

NumWorks provide a pure Rust sample application themselves, but it had some problems for me:

• Calculator crash and reset when trying to call eadk_display_draw_string
• Intermittent crashes or unexpected behaviour when drawing to the screen

On the contrary, I had no issues using the Epsilon C example app.

My best guesses are either: Rust's compiler toolchain making decisions about memory allocation which NumWorks doesn't like; or an EABI incompatibility between Epsilon's EADK libraries and Rust.

So I decided to create a new sample application based on that C example, which compiles and links a Rust static library. EADK APIs are usable through a provided eadk_bridge, which wraps EADK functions with "simpler" signatures to reduce the chance of EABI problems.

// Original EADK API
typedef struct {
  uint16_t x;
  uint16_t y;
  uint16_t width;
  uint16_t height;
} eadk_rect_t;
typedef uint16_t eadk_color_t;
eadk_display_push_rect_uniform(eadk_rect_t rect, eadk_color_t color);

// Wrapped `eadk_bridge` API
eadk_bridge__display_push_rect_uniform(uint16_t x, uint16_t y, uint16_t width, uint16_t height, uint16_t color);

Features

Most of the important EADK APIs are broken out into nice, high-level Rust APIs. For example:

display::write_string(
  "Hello from Rust!",
  Point { x: 50, y: 50 },
  Font::Large,
  Color::BLACK,
  Color::WHITE,
);

timing::msleep(1000);

There is also a GlobalAlloc implementation, so you can use the alloc crate.

Compatibility

This was developed/tested on:

• nwlink 0.0.17, running on Node 18.19.0
• Rust 1.71.0-nightly (c609da59d 2023-04-18)
• NumWorks N0120, running Epsilon 21.3.0

Usage

The same dependencies apply as the Epsilon C example app which this is derived from.

Once installed, you can build an NWA and run it on your calculator:

make build  # Build Rust and C parts into NWA
make check  # Ensure that NWA links successfully
make run    # Upload to calculator

Layout

src includes C source code, including the main and eadk_bridge definitions. You probably don't need to edit any of the C files in here, besides the app name in main.c.

rs contains the Rust code. In lib.rs you'll find the entry point, rs_main.