Made an example for the SSD1306 OLED display

ssd1306_oled_display/.cargo/config

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+[target.'cfg(all(target_arch = "arm", target_os = "none"))']
+runner = "probe-run-rp --chip RP2040"
+
+rustflags = [
+  "-C", "linker=flip-link",
+  "-C", "link-arg=--nmagic",
+  "-C", "link-arg=-Tlink.x",
+  "-C", "link-arg=-Tdefmt.x",
+
+  # Code-size optimizations.
+  #   trap unreachable can save a lot of space, but requires nightly compiler.
+  #   uncomment the next line if you wish to enable it
+  # "-Z", "trap-unreachable=no",
+  "-C", "inline-threshold=5",
+  "-C", "no-vectorize-loops",
+]
+
+[build]
+target = "thumbv6m-none-eabi"

ssd1306_oled_display/.gitignore

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+**/*.rs.bk
+.#*
+.gdb_history
+Cargo.lock
+target/
+
+# editor files
+.vscode/*
+!.vscode/*.md
+!.vscode/*.svd
+!.vscode/launch.json
+!.vscode/tasks.json
+!.vscode/extensions.json
+!.vscode/settings.json
+
+*.history

ssd1306_oled_display/Cargo.toml

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+[package]
+authors = ["Weird Constructor"]
+edition = "2018"
+readme = "README.md"
+name = "rp2040-ws2812-led-cube"
+version = "0.1.0"
+resolver = "2"
+
+[dependencies]
+cortex-m = "0.7.3"
+cortex-m-rt = "0.7.0"
+embedded-hal = { version = "0.2.5", features=["unproven"] }
+embedded-time = "0.12.0"
+
+defmt = "0.2.0"
+defmt-rtt = "0.2.0"
+panic-probe = { version = "0.2.0", features = ["print-defmt"] }
+
+#rp2040-hal = { git = "https://github.com/rp-rs/rp-hal", branch="main", features=["rt"] }
+rp2040-boot2 = { git = "https://github.com/rp-rs/rp2040-boot2-rs", branch="main" }
+pico = { git = "https://github.com/rp-rs/rp-hal.git", branch="main" }
+
+ssd1306 = "0.7.0"
+embedded-graphics = "0.7.1"
+
+nb = "1.0"
+
+[features]
+default = [
+    "defmt-default",
+]
+defmt-default = []
+defmt-trace = []
+defmt-debug = []
+defmt-info = []
+defmt-warn = []
+defmt-error = []
+
+# cargo build/run
+[profile.dev]
+codegen-units = 1
+debug = 2
+debug-assertions = true
+incremental = false
+opt-level = 3
+overflow-checks = true
+
+# cargo build/run --release
+[profile.release]
+codegen-units = 1
+debug = 2
+debug-assertions = false
+incremental = false
+lto = 'fat'
+opt-level = 3
+overflow-checks = false
+
+# do not optimize proc-macro crates = faster builds from scratch
+[profile.dev.build-override]
+codegen-units = 8
+debug = false
+debug-assertions = false
+opt-level = 0
+overflow-checks = false
+
+[profile.release.build-override]
+codegen-units = 8
+debug = false
+debug-assertions = false
+opt-level = 0
+overflow-checks = false
+
+# cargo test
+[profile.test]
+codegen-units = 1
+debug = 2
+debug-assertions = true
+incremental = false
+opt-level = 3
+overflow-checks = true
+
+# cargo test --release
+[profile.bench]
+codegen-units = 1
+debug = 2
+debug-assertions = false
+incremental = false
+lto = 'fat'
+opt-level = 3
+
+[dependencies.num-traits]
+version = "0.2.14"
+default-features = false

ssd1306_oled_display/build.rs

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+//! This build script copies the `memory.x` file from the crate root into
+//! a directory where the linker can always find it at build time.
+//! For many projects this is optional, as the linker always searches the
+//! project root directory -- wherever `Cargo.toml` is. However, if you
+//! are using a workspace or have a more complicated build setup, this
+//! build script becomes required. Additionally, by requesting that
+//! Cargo re-run the build script whenever `memory.x` is changed,
+//! updating `memory.x` ensures a rebuild of the application with the
+//! new memory settings.
+
+use std::env;
+use std::fs::File;
+use std::io::Write;
+use std::path::PathBuf;
+
+fn main() {
+    // Put `memory.x` in our output directory and ensure it's
+    // on the linker search path.
+    let out = &PathBuf::from(env::var_os("OUT_DIR").unwrap());
+    File::create(out.join("memory.x"))
+        .unwrap()
+        .write_all(include_bytes!("memory.x"))
+        .unwrap();
+    println!("cargo:rustc-link-search={}", out.display());
+
+    // By default, Cargo will re-run a build script whenever
+    // any file in the project changes. By specifying `memory.x`
+    // here, we ensure the build script is only re-run when
+    // `memory.x` is changed.
+    println!("cargo:rerun-if-changed=memory.x");
+}

ssd1306_oled_display/memory.x

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+MEMORY {
+    BOOT2 : ORIGIN = 0x10000000, LENGTH = 0x100
+    FLASH : ORIGIN = 0x10000100, LENGTH = 2048K - 0x100
+    RAM   : ORIGIN = 0x20000000, LENGTH = 256K
+}
+
+SECTIONS {
+    /* ### Boot loader */
+    .boot2 ORIGIN(BOOT2) :
+    {
+        KEEP(*(.boot2));
+    } > BOOT2
+} INSERT BEFORE .text;

ssd1306_oled_display/src/main.rs

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+#![no_std]
+#![no_main]
+
+use cortex_m_rt::entry;
+use defmt::*;
+use defmt_rtt as _;
+use embedded_time::duration::*;
+use embedded_time::rate::Extensions;
+use embedded_hal::timer::CountDown;
+use panic_probe as _;
+
+use embedded_hal::adc::OneShot;
+use embedded_hal::blocking::i2c::Write;
+use pico::hal::{
+    pac,
+    clocks::{Clock, init_clocks_and_plls},
+    sio::Sio,
+    adc::Adc,
+    gpio,
+    i2c::I2C,
+    watchdog::Watchdog,
+    timer::Timer,
+};
+use embedded_graphics::{
+    mono_font::{ascii::FONT_9X18_BOLD, MonoTextStyleBuilder},
+    pixelcolor::BinaryColor,
+    prelude::*,
+    text::{Baseline, Text},
+};
+use ssd1306::{prelude::*, I2CDisplayInterface, Ssd1306};
+
+use pico::hal::pio::PIOExt;
+
+#[link_section = ".boot2"]
+#[used]
+pub static BOOT2: [u8; 256] = rp2040_boot2::BOOT_LOADER_W25Q080;
+
+struct FmtBuf {
+    buf: [u8; 64],
+    ptr: usize,
+}
+
+impl FmtBuf {
+    fn new() -> Self {
+        Self { buf: [0; 64], ptr: 0 }
+    }
+
+    fn as_str(&self) -> &str {
+        unsafe {
+            core::str::from_utf8_unchecked(&self.buf[0..self.ptr])
+        }
+    }
+}
+
+impl core::fmt::Write for FmtBuf {
+    fn write_str(&mut self, s: &str) -> core::fmt::Result {
+        let len = s.len();
+        self.buf[self.ptr..(self.ptr + len)].copy_from_slice(s.as_bytes());
+        self.ptr += len;
+        Ok(())
+    }
+}
+
+
+#[entry]
+fn main() -> ! {
+    info!("Program start");
+    let mut pac      = pac::Peripherals::take().unwrap();
+    let _core         = pac::CorePeripherals::take().unwrap();
+    let mut watchdog = Watchdog::new(pac.WATCHDOG);
+    let sio          = Sio::new(pac.SIO);
+
+    // External high-speed crystal on the pico board is 12Mhz
+    let external_xtal_freq_hz = 12_000_000u32;
+    let clocks =
+        init_clocks_and_plls(
+            external_xtal_freq_hz,
+            pac.XOSC,
+            pac.CLOCKS,
+            pac.PLL_SYS,
+            pac.PLL_USB,
+            &mut pac.RESETS,
+            &mut watchdog)
+        .ok()
+        .unwrap();
+
+    let pins = pico::Pins::new(
+        pac.IO_BANK0,
+        pac.PADS_BANK0,
+        sio.gpio_bank0,
+        &mut pac.RESETS,
+    );
+
+    // Configure two pins as being I²C, not GPIO
+    let sda_pin = pins.gpio16.into_mode::<gpio::FunctionI2C>();
+    let scl_pin = pins.gpio17.into_mode::<gpio::FunctionI2C>();
+
+    // Create the I²C drive, using the two pre-configured pins. This will fail
+    // at compile time if the pins are in the wrong mode, or if this I²C
+    // peripheral isn't available on these pins!
+    let mut i2c = I2C::i2c0(
+        pac.I2C0,
+        sda_pin,
+        scl_pin,
+        400.kHz(),
+        &mut pac.RESETS,
+        clocks.peripheral_clock,
+    );
+
+    let interface = I2CDisplayInterface::new(i2c);
+    let mut display =
+        Ssd1306::new(interface, DisplaySize128x64, DisplayRotation::Rotate0)
+        .into_buffered_graphics_mode();
+    display.init().unwrap();
+
+    let text_style = MonoTextStyleBuilder::new()
+        .font(&FONT_9X18_BOLD)
+        .text_color(BinaryColor::On)
+        .build();
+
+    let timer = Timer::new(pac.TIMER, &mut pac.RESETS);
+    let mut delay = timer.count_down();
+
+    let mut count = 0;
+
+    loop {
+        let mut buf = FmtBuf::new();
+        core::fmt::write(&mut buf, format_args!("counter: {}", count));
+
+        count += 1;
+
+        display.clear();
+        Text::with_baseline("Hello world!", Point::zero(), text_style, Baseline::Top)
+            .draw(&mut display)
+            .unwrap();
+
+        Text::with_baseline("Hello Rust!", Point::new(0, 16), text_style, Baseline::Top)
+            .draw(&mut display)
+            .unwrap();
+
+        Text::with_baseline(buf.as_str(), Point::new(0, 32), text_style, Baseline::Top)
+            .draw(&mut display)
+            .unwrap();
+        display.flush().unwrap();
+
+
+        delay.start(500.milliseconds());
+        let _ = nb::block!(delay.wait());
+    }
+}