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Add Raspberry Pi 4B & 5 baremetal examples (#67)
Provide new examples demonstrating how to run Swift Embedded on the Raspberry Pi 4B and 5 single-board computers, in a baremetal fashion, without an underlying operating system. The provided examples showcase how to blink the onboard green LED using Swift MMIO.
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‎.github/workflows/build-rpi-baremetal.yml

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name: Build Raspberry Pi Baremetal Examples
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on:
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push:
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branches: ["main"]
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pull_request:
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branches: ["main"]
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schedule:
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# Build on Mondays at 9am PST every week
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- cron: '0 17 * * 1'
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jobs:
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build-rpi-baremetal:
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runs-on: ubuntu-24.04
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strategy:
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fail-fast: false
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matrix:
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example: [rpi5-blink, rpi4b-blink]
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swift: [swift-DEVELOPMENT-SNAPSHOT-2024-12-04-a]
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steps:
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- name: Checkout repo
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uses: actions/checkout@v4
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- name: Install apt dependencies
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run: sudo apt-get -qq update && sudo apt-get -qq -y install make llvm
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- name: Install ${{ matrix.swift }}
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run: |
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wget -q https://download.swift.org/development/ubuntu2404/${{ matrix.swift }}/${{ matrix.swift }}-ubuntu24.04.tar.gz
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tar xzf ${{ matrix.swift }}-ubuntu24.04.tar.gz
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export PATH="`pwd`/${{ matrix.swift }}-ubuntu24.04/usr/bin/:$PATH"
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echo "PATH=$PATH" >> $GITHUB_ENV
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which swiftc
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swiftc --version
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- name: Build ${{ matrix.example }}
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run: |
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cd ${{ matrix.example }}
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make

‎README.md

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| [pico-blink](./pico-blink) | Raspberry Pi Pico | None | Blink an LED repeatedly. | <img width="300" src="https://github.com/apple/swift-embedded-examples/assets/1186214/f2c45c18-f9a4-48b4-a941-1298ecc942cb"> |
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| [pico-w-blink-sdk](./pico-w-blink-sdk) | Raspberry Pi Pico W | Pico SDK | Blink an LED to signal 'SOS' in Morse code repeatedly with Swift & the Pico SDK. | <img width="300" src="https://github.com/apple/swift-embedded-examples/assets/26223064/a4949a2e-1887-4325-8f5f-a681963c93d7"> |
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| [pico2-neopixel](./pico2-neopixel) | Raspberry Pi Pico 2 | None | Control Neopixel LEDs using the RP2350 PIO. | <img width="300" src="pico2-neopixel/assets/images/example.jpg"> |
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| [rpi4b-blink](./rpi4b-blink) | Raspberry Pi 4B | None | Blink the Pi's status green LED repeatedly using Swift MMIO. | <img width="300" src="rpi4b-blink/assets/rpi4.png"> |
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| [rpi5-blink](./rpi5-blink) | Raspberry Pi 5 | None | Blink the Pi's status green LED repeatedly with Swift MMIO. | <img width="300" src="rpi5-blink/assets/raspi5.png"> |
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| [stm32-blink](./stm32-blink) | STM32F746G-DISCO | None | Blink an LED repeatedly. | <img width="300" src="https://github.com/apple/swift-embedded-examples/assets/1186214/739e98fd-a438-4a64-a7aa-9dddee25034b"> |
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| [stm32-lcd-logo](./stm32-lcd-logo) | STM32F746G-DISCO | None | Animate the Swift Logo on the built-in LCD. | <img width="300" src="https://github.com/apple/swift-embedded-examples/assets/1186214/9e117d81-e808-493e-a20c-7284ea630f37"> |
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| [stm32-neopixel](./stm32-neopixel) | STM32F746G-DISCO | None | Control NeoPixel LEDs using SPI. | <img width="300" src="https://github.com/apple/swift-embedded-examples/assets/1186214/9c5d8f74-f8aa-4632-831e-212a3e35e75a"> |

‎rpi4b-blink/Makefile

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SWIFT_EXEC ?= $(shell if [ "$(shell uname)" = "Darwin" ]; then xcrun -f swift; else which swift; fi)
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CLANG ?= $(shell if [ "$(shell uname)" = "Darwin" ]; then xcrun -f clang; else which clang; fi)
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LLVM_OBJCOPY ?= $(shell if [ "$(shell uname)" = "Darwin" ]; then xcrun -f llvm-objcopy; else which llvm-objcopy; fi)
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BUILDROOT := $(shell $(SWIFT_EXEC) build --triple aarch64-none-none-elf -Xswiftc -Xfrontend -Xswiftc -disable-stack-protector --show-bin-path)
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.PHONY: all clean
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all: kernel8.img
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kernel8.img: kernel8.elf
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@echo "💾 Converting to binary kernel image with llvm-objcopy..."
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$(LLVM_OBJCOPY) -O binary kernel8.elf kernel8.img
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@echo ""
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@echo "🥳 Done! kernel8.img was saved to this directory."
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kernel8.elf: $(BUILDROOT)/libMainApp.a $(BUILDROOT)/Support.build/boot.S.o link.ld
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@echo "🔗 Linking with clang..."
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$(CLANG) --target=aarch64-elf -o kernel8.elf $< $^ -fuse-ld=lld -nostdlib -Wl,--unresolved-symbols=ignore-in-object-files -Wl,-T ./link.ld
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@echo ""
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$(BUILDROOT)/libMainApp.a $(BUILDROOT)/Support.build/boot.S.o:
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@echo "🛠️ Building with Swift Package Manager..."
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$(SWIFT_EXEC) build --triple aarch64-none-none-elf -Xswiftc -Xfrontend -Xswiftc -disable-stack-protector
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@echo ""
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clean:
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rm -rf kernel8.elf kernel8.img .build

‎rpi4b-blink/Package.swift

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// swift-tools-version: 6.1
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// The swift-tools-version declares the minimum version of Swift required to build this package.
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import PackageDescription
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let package = Package(
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name: "RPi4B-Blink",
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platforms: [
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.macOS(.v14)
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],
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products: [
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.library(
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name: "MainApp",
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type: .static,
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targets: ["MainApp"])
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],
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dependencies: [
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.package(
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url: "https://github.com/apple/swift-mmio.git",
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branch: "swift-embedded-examples")
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],
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targets: [
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.target(
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name: "MainApp",
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dependencies: [
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.product(name: "MMIO", package: "swift-mmio")
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],
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swiftSettings: [
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.enableExperimentalFeature("Embedded"),
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.unsafeFlags(["-Xfrontend", "-function-sections"]),
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]
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),
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.target(name: "Support"),
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]
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)

‎rpi4b-blink/README.md

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# rpi4b-blink
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<img src="assets/rpi4.png">
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## Requirements
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- A Raspberry Pi 4B board
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- An SD Card, with a Raspberry Pi OS installed (this way, we don't need to create the configuration files from scratch). You may backup `kernel8.img` and `config.txt` if you need the Linux install later, since we will change these files.
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- LLVM installed (`brew install llvm`) and added to PATH. This is needed to convert the resulted ELF file to binary image format using `llvm-objcopy`.
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## How to build and run this example:
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- Make sure you have a recent nightly Swift toolchain that has Embedded Swift support.
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- Build the program, then copy the kernel image to the SD card.
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``` console
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$ cd rpi4b-blink
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$ export TOOLCHAINS='<toolchain-identifier>' # Your Swift nightly toolchain identifier
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$ make
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$ cp kernel8.img /Volumes/bootfs
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```
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- If your original OS is not 64-bit, make sure to set `arm_64bit=1` in `config.txt`.
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- Place the SD card in your Raspberry Pi 4B, and connect it to power.
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- After the boot sequence, the green (ACT) led will start blinking in a regular pattern.
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‎rpi4b-blink/Sources/MainApp/MainApp.swift

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//===----------------------------------------------------------------------===//
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//
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// This source file is part of the Swift open source project
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//
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// Copyright (c) 2024 Apple Inc. and the Swift project authors.
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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//
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//===----------------------------------------------------------------------===//
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import MMIO
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@Register(bitWidth: 32)
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struct GPSET1 {
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@ReadWrite(bits: 10..<11, as: Bool.self)
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var set: SET
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}
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@Register(bitWidth: 32)
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struct GPCLR1 {
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@ReadWrite(bits: 10..<11, as: Bool.self)
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var clear: CLEAR
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}
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@Register(bitWidth: 32)
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struct GPFSEL4 {
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@ReadWrite(bits: 6..<7, as: Bool.self)
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var fsel42b1: FSEL42b1
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@ReadWrite(bits: 7..<8, as: Bool.self)
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var fsel42b2: FSEL42b2
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@ReadWrite(bits: 8..<9, as: Bool.self)
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var fsel42b3: FSEL42b3
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}
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@RegisterBlock
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struct GPIO {
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@RegisterBlock(offset: 0x200020)
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var gpset1: Register<GPSET1>
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@RegisterBlock(offset: 0x20002c)
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var gpclr1: Register<GPCLR1>
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@RegisterBlock(offset: 0x200010)
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var gpfsel4: Register<GPFSEL4>
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}
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let gpio = GPIO(unsafeAddress: 0xFE00_0000)
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func setLedOutput() {
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gpio.gpfsel4.modify {
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// setFunction Select 42 (fsel42) to 001
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$0.fsel42b1 = true
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$0.fsel42b2 = false
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$0.fsel42b3 = false
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}
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}
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func ledOn() {
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gpio.gpset1.modify {
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$0.set = true
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}
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}
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func ledOff() {
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gpio.gpclr1.modify {
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$0.clear = true
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}
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}
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@main
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struct Main {
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static func main() {
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setLedOutput()
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while true {
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ledOn()
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for _ in 1..<100000 {} // just a delay
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ledOff()
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for _ in 1..<100000 {} // just a delay
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}
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}
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}

‎rpi4b-blink/Sources/Support/boot.S

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//===----------------------------------------------------------------------===//
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//
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// This source file is part of the Swift open source project
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//
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// Copyright (c) 2024 Apple Inc. and the Swift project authors.
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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//
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//===----------------------------------------------------------------------===//
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.section ".text.boot"
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.global _start
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_start:
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// Check processor ID is zero (executing on main core), else hang
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mrs x1, mpidr_el1
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and x1, x1, #3
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cbz x1, 2f
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// We're not on the main core, so hang in an infinite wait loop
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1: wfe
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b 1b
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2: // We're on the main core!
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// Set stack to start below our code
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ldr x1, =_start
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mov sp, x1
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// Clean the BSS section
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ldr x1, =__bss_start // Start address
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ldr w2, =__bss_size // Size of the section
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3: cbz w2, 4f // Quit loop if zero
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str xzr, [x1], #8
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sub w2, w2, #1
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cbnz w2, 3b // Loop if non-zero
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// Jump to Swift!
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4: bl main
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// Halt if Swift returns
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b 1b

‎rpi4b-blink/Sources/Support/include/boot.h

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‎rpi4b-blink/assets/rpi4.png

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‎rpi4b-blink/link.ld

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SECTIONS
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{
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. = 0x80000; /* Kernel load address for AArch64 */
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.text : { KEEP(*(.text.boot)) *(.text .text.* .gnu.linkonce.t*) }
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.rodata : { *(.rodata .rodata.* .gnu.linkonce.r*) }
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PROVIDE(_data = .);
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.data : { *(.data .data.* .gnu.linkonce.d*) }
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.bss (NOLOAD) : {
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. = ALIGN(16);
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__bss_start = .;
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*(.bss .bss.*)
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*(COMMON)
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__bss_end = .;
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}
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_end = .;
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/DISCARD/ : { *(.comment) *(.gnu*) *(.note*) *(.eh_frame*) }
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}
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__bss_size = (__bss_end - __bss_start)>>3;

‎rpi5-blink/Makefile

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SWIFT_EXEC ?= $(shell if [ "$(shell uname)" = "Darwin" ]; then xcrun -f swift; else which swift; fi)
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CLANG ?= $(shell if [ "$(shell uname)" = "Darwin" ]; then xcrun -f clang; else which clang; fi)
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LLVM_OBJCOPY ?= $(shell if [ "$(shell uname)" = "Darwin" ]; then xcrun -f llvm-objcopy; else which llvm-objcopy; fi)
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BUILDROOT := $(shell $(SWIFT_EXEC) build --triple aarch64-none-none-elf -Xswiftc -Xfrontend -Xswiftc -disable-stack-protector --show-bin-path)
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.PHONY: all clean
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all: kernel8.img
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kernel8.img: kernel8.elf
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@echo "💾 Converting to binary kernel image with llvm-objcopy..."
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$(LLVM_OBJCOPY) -O binary kernel8.elf kernel8.img
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@echo ""
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@echo "🥳 Done! kernel8.img was saved to this directory."
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kernel8.elf: $(BUILDROOT)/libMainApp.a $(BUILDROOT)/Support.build/boot.S.o link.ld
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@echo "🔗 Linking with clang..."
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$(CLANG) --target=aarch64-elf -o kernel8.elf $< $^ -fuse-ld=lld -nostdlib -Wl,--unresolved-symbols=ignore-in-object-files -Wl,-T ./link.ld
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@echo ""
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$(BUILDROOT)/libMainApp.a $(BUILDROOT)/Support.build/boot.S.o:
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@echo "🛠️ Building with Swift Package Manager..."
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$(SWIFT_EXEC) build --triple aarch64-none-none-elf -Xswiftc -Xfrontend -Xswiftc -disable-stack-protector
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@echo ""
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clean:
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rm -rf kernel8.elf kernel8.img .build

‎rpi5-blink/Package.resolved

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{
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"originHash" : "193ca3f107e2c8dd2da5d091f6259f64b2cbfd6776d1c26bbcfb195b3a0b5045",
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"pins" : [
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{
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"identity" : "swift-argument-parser",
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"kind" : "remoteSourceControl",
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"location" : "https://github.com/apple/swift-argument-parser.git",
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"state" : {
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"revision" : "41982a3656a71c768319979febd796c6fd111d5c",
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"version" : "1.5.0"
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}
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},
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{
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"identity" : "swift-mmio",
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"kind" : "remoteSourceControl",
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"location" : "https://github.com/apple/swift-mmio.git",
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"state" : {
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"branch" : "swift-embedded-examples",
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"revision" : "06d96ed4916739f2edafde87f3951b2d2a04df65"
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}
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},
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{
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"identity" : "swift-syntax",
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"kind" : "remoteSourceControl",
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"location" : "https://github.com/swiftlang/swift-syntax.git",
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"state" : {
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"revision" : "0687f71944021d616d34d922343dcef086855920",
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"version" : "600.0.1"
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}
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}
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],
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"version" : 3
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}

‎rpi5-blink/Package.swift

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// swift-tools-version: 6.1
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// The swift-tools-version declares the minimum version of Swift required to build this package.
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import PackageDescription
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let package = Package(
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name: "RPi5-Blink",
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platforms: [
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.macOS(.v14)
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],
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products: [
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.library(
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name: "MainApp",
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type: .static,
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targets: ["MainApp"])
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],
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dependencies: [
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.package(
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url: "https://github.com/apple/swift-mmio.git",
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branch: "swift-embedded-examples")
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],
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targets: [
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.target(
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name: "MainApp",
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dependencies: [
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.product(name: "MMIO", package: "swift-mmio")
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],
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swiftSettings: [
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.enableExperimentalFeature("Embedded"),
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.unsafeFlags(["-Xfrontend", "-function-sections"]),
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]
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),
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.target(name: "Support"),
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]
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)

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