Lib.rs

This library contains a driver for E-Paper Modules with Controller GDE021A1 ((172x72 B/W Pixel via SPI)).

It uses the embedded graphics library for the optional graphics support.

A 2018-edition compatible version (Rust 1.31+) is needed.

Resource Needs

• The GED021A1 ePaper Display is Black/White (4 gray levels per pixel)
• Each Pixel value is encoded by 2 bit.
• Before the ePaper display is refreshed all data is written into RAM. A RAM cache storage of (2 bit per 172 x 72 Pixels equals to) 3096 Bytes is mandatory.
• Besides the RAM only the typical SPI peripherals (clock, CLK pin MOSI pin,) and additional arbitrary GPIO pins (Data/Command, Busy, Reset) are needed.

Usage

For example, the initialize sequence is like (on a Cortex MCU, using the embedded hal crate)

Set the default compile target in e.g .cargo/config file to

[build]
target = "thumbv6m-none-eabi"    # Cortex-M0 and Cortex-M0+

in order to support Cortex-M0.

    let dp = pac::Peripherals::take().unwrap();
    let cp = cortex_m::Peripherals::take().unwrap();

    // Configure the clock.
    let mut rcc = dp.RCC.freeze(Config::hsi16());

    // Acquire the GPIOx peripheral.
    // This also enables the clock for GPIOx in the RCC register.
    let gpioa = dp.GPIOA.split(&mut rcc);
    let gpiob = dp.GPIOB.split(&mut rcc);

    // The GPIO's
    let chip_sel = gpioa.pa15.into_push_pull_output();
    let data_cmd = gpiob.pb11.into_push_pull_output();
    let reset = gpiob.pb2.into_push_pull_output();
    let busy = gpiob.pb8.into_pull_up_input();

    // The SPI
    let mosi = gpiob.pb5;
    let clk = gpiob.pb3;
    let spi = dp.SPI1.spi((clk, NoMiso, mosi), MODE_0, 1_000_000.hz(), &mut rcc);

    // the time delay
    let mut delay = cp.SYST.delay(rcc.clocks);

    // and finally the display structure
    let mut disp =  GDE021A1::new(spi, reset, Some(chip_sel), data_cmd, busy);
    // initialize the display
    disp.init(&mut delay).expect("could not init display");

Once the display is initialized it can be used using the embedded graphics library like e.g. like

    // all pixels turn white
    disp.clear();

    // draw some fancy stuff and graphics via embedded graphics api
    let elem =  Circle::new(Point::new(140, 36), 25)
         .into_styled(PrimitiveStyle::with_fill(BinaryColor::On));
    elem.draw(&mut disp);
    let elem = Text::new("Hello Rust!", Point::new(1, 8))
        .into_styled(TextStyle::new(Font6x8, BinaryColor::On));
    elem.draw(&mut disp);

    // refresh the epaper
    disp.refresh(&mut delay).expect("could not flush display");

Testing

The embedded target is most likely very different from the host. and pre-configured in your .cargo/config file. However, test (specifically in CI environment run on host)

Thus, tests can savely run by specifying your host target like

cargo test --target=x86_64-unknown-linux-gnu

Interface

Credits

• Waveshare EPD driver
• SSD1306 OLED display driver
• Sample C++ Source from STM
• GDE021A1 Specification
• GxEPD in C++