Raspberry Pi 4B & 5 baremetal blink example

.github/workflows/build-rpi-baremetal.yml

@@ -0,0 +1,31 @@
+name: Build Raspberry Pi Baremetal Examples
+
+on:
+  push:
+    branches: ["main"]
+  pull_request:
+    branches: ["main"]
+  schedule:
+    # Build on Mondays at 9am PST every week
+    - cron:  '0 17 * * 1'
+
+jobs:
+  build-pico-sdk:
+    runs-on: ubuntu-22.04
+    container: swiftlang/swift:nightly-main-jammy
+    strategy:
+      fail-fast: false
+      matrix:
+        example: [rpi5-blink, rpi4b-blink]
+
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v4
+
+      - name: Install apt dependencies
+        run: apt-get -qq update && apt-get -qq -y install make llvm
+
+      - name: Build ${{ matrix.example }}
+        run: |
+          cd ${{ matrix.example }}
+          make

README.md

@@ -43,6 +43,8 @@ Each example in this repository contains build and deployment instructions, howe
 | [nrfx-blink-sdk](./nrfx-blink-sdk) | nRF52840-DK | Zephyr SDK | Blink an LED repeatedly with Swift & Zephyr. | <img width="300" src="https://github.com/apple/swift-embedded-examples/assets/1186214/ae3ff153-dd33-4460-8a08-4eac442bf7b0"> |
 | [esp32-led-strip-sdk](./esp32-led-strip-sdk) | ESP32-C6-DevKitC-1 | ESP-IDF SDK | Control NeoPixel LEDs with Swift & the ESP-IDF. | <img width="300" src="https://github.com/apple/swift-embedded-examples/assets/1186214/15f8a3e0-953e-426d-ad2d-3902baf859be"> |
 | [esp32-led-blink-sdk](./esp32-led-blink-sdk) | ESP32-C6-Bug | ESP-IDF SDK | Blink an LED repeatedly with Swift & the ESP-IDF. | <img width="300" src="esp32-led-blink-sdk/assets/images/ledon.jpg"> |
+| [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"> |
+| [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"> |
 
 Note that the SDK integration examples (Pico SDK, Zephyr SDK, etc.) are not recommendations or endorsement, the same is true for build system choice (Make, CMake, SwiftPM, shell scripts). Embedded Swift aims to be versatile and to allow for integration into more existing SDKs and build systems, and the example projects are merely showing the possibilities.
 

rpi4b-blink/Makefile

@@ -0,0 +1,28 @@
+SWIFT_EXEC ?= $(shell if [ "$(shell uname)" = "Darwin" ]; then xcrun -f swift; else which swift; fi)
+CLANG ?= $(shell if [ "$(shell uname)" = "Darwin" ]; then xcrun -f clang; else which clang; fi)
+LLVM_OBJCOPY ?= $(shell if [ "$(shell uname)" = "Darwin" ]; then xcrun -f llvm-objcopy; else which llvm-objcopy; fi)
+
+BUILDROOT := $(shell $(SWIFT_EXEC) build --triple aarch64-none-none-elf -Xswiftc -Xfrontend -Xswiftc -disable-stack-protector --show-bin-path)
+
+.PHONY: all clean
+
+all: kernel8.img
+
+kernel8.img: kernel8.elf
+	@echo "💾 Converting to binary kernel image with llvm-objcopy..."
+	$(LLVM_OBJCOPY) -O binary kernel8.elf kernel8.img
+	@echo ""
+	@echo "🥳 Done! kernel8.img was saved to this directory."
+
+kernel8.elf: $(BUILDROOT)/libMainApp.a $(BUILDROOT)/Support.build/boot.S.o link.ld
+	@echo "🔗 Linking with clang..."
+	$(CLANG) --target=aarch64-elf -o kernel8.elf $< $^ -fuse-ld=lld -nostdlib -Wl,--unresolved-symbols=ignore-in-object-files -Wl,-T ./link.ld
+	@echo ""
+
+$(BUILDROOT)/libMainApp.a $(BUILDROOT)/Support.build/boot.S.o: 
+	@echo "🛠️  Building with Swift Package Manager..."
+	$(SWIFT_EXEC) build --triple aarch64-none-none-elf -Xswiftc -Xfrontend -Xswiftc -disable-stack-protector
+	@echo ""
+
+clean:
+	rm -rf kernel8.elf kernel8.img .build

rpi4b-blink/Package.swift

@@ -0,0 +1,36 @@
+// swift-tools-version: 6.1
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+  name: "RPi4B-Blink",
+  platforms: [
+    .macOS(.v14)
+  ],
+  products: [
+    .library(
+      name: "MainApp",
+      type: .static,
+      targets: ["MainApp"])
+  ],
+  dependencies: [
+    .package(
+      url: "https://github.com/apple/swift-mmio.git",
+      branch: "swift-embedded-examples")
+  ],
+  targets: [
+    .target(
+      name: "MainApp",
+      dependencies: [
+        .product(name: "MMIO", package: "swift-mmio")
+      ],
+      swiftSettings: [
+        .enableExperimentalFeature("Embedded"),
+        .unsafeFlags(["-Xfrontend", "-function-sections"]),
+      ]
+    ),
+    .target(name: "Support"),
+
+  ]
+)

rpi4b-blink/README.md

@@ -0,0 +1,24 @@
+# rpi4b-blink
+
+<img src="assets/rpi4.png">
+
+## Requirements
+
+- A Raspberry Pi 4B board
+- 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.
+- 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`.
+
+## How to build and run this example:
+
+- Make sure you have a recent nightly Swift toolchain that has Embedded Swift support.
+- Build the program, then copy the kernel image to the SD card.
+``` console
+$ cd rpi4b-blink
+$ export TOOLCHAINS='<toolchain-identifier>' # Your Swift nightly toolchain identifier
+$ make
+$ cp kernel8.img /Volumes/bootfs
+```
+- If your original OS is not 64-bit, make sure to set `arm_64bit=1` in `config.txt`.
+- Place the SD card in your Raspberry Pi 4B, and connect it to power.
+- After the boot sequence, the green (ACT) led will start blinking in a regular pattern.
+

rpi4b-blink/Sources/MainApp/MainApp.swift

@@ -0,0 +1,82 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2024 Apple Inc. and the Swift project authors.
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+import MMIO
+
+@Register(bitWidth: 32)
+struct GPSET1 {
+  @ReadWrite(bits: 10..<11, as: Bool.self)
+  var set: SET
+}
+
+@Register(bitWidth: 32)
+struct GPCLR1 {
+  @ReadWrite(bits: 10..<11, as: Bool.self)
+  var clear: CLEAR
+}
+
+@Register(bitWidth: 32)
+struct GPFSEL4 {
+  @ReadWrite(bits: 6..<7, as: Bool.self)
+  var fsel42b1: FSEL42b1
+  @ReadWrite(bits: 7..<8, as: Bool.self)
+  var fsel42b2: FSEL42b2
+  @ReadWrite(bits: 8..<9, as: Bool.self)
+  var fsel42b3: FSEL42b3
+}
+
+@RegisterBlock
+struct GPIO {
+  @RegisterBlock(offset: 0x200020)
+  var gpset1: Register<GPSET1>
+  @RegisterBlock(offset: 0x20002c)
+  var gpclr1: Register<GPCLR1>
+  @RegisterBlock(offset: 0x200010)
+  var gpfsel4: Register<GPFSEL4>
+}
+
+let gpio = GPIO(unsafeAddress: 0xFE00_0000)
+
+func setLedOutput() {
+  gpio.gpfsel4.modify {
+    // setFunction Select 42 (fsel42) to 001
+    $0.fsel42b1 = true
+    $0.fsel42b2 = false
+    $0.fsel42b3 = false
+  }
+}
+
+func ledOn() {
+  gpio.gpset1.modify {
+    $0.set = true
+  }
+}
+
+func ledOff() {
+  gpio.gpclr1.modify {
+    $0.clear = true
+  }
+}
+
+@main
+struct Main {
+
+  static func main() {
+    setLedOutput()
+
+    while true {
+      ledOn()
+      for _ in 1..<100000 {}  // just a delay
+      ledOff()
+      for _ in 1..<100000 {}  // just a delay
+    }
+  }
+}

rpi4b-blink/Sources/Support/boot.S

@@ -0,0 +1,41 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2024 Apple Inc. and the Swift project authors.
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+.section ".text.boot"
+
+.global _start
+
+_start:
+    // Check processor ID is zero (executing on main core), else hang
+    mrs     x1, mpidr_el1
+    and     x1, x1, #3
+    cbz     x1, 2f
+    // We're not on the main core, so hang in an infinite wait loop
+1:  wfe
+    b       1b
+2:  // We're on the main core!
+
+    // Set stack to start below our code
+    ldr     x1, =_start
+    mov     sp, x1
+
+    // Clean the BSS section
+    ldr     x1, =__bss_start     // Start address
+    ldr     w2, =__bss_size      // Size of the section
+3:  cbz     w2, 4f               // Quit loop if zero
+    str     xzr, [x1], #8
+    sub     w2, w2, #1
+    cbnz    w2, 3b               // Loop if non-zero
+
+    // Jump to Swift!
+4:  bl      main
+    // Halt if Swift returns
+    b       1b

rpi4b-blink/link.ld

@@ -0,0 +1,19 @@
+SECTIONS
+{
+    . = 0x80000;     /* Kernel load address for AArch64 */
+    .text : { KEEP(*(.text.boot)) *(.text .text.* .gnu.linkonce.t*) }
+    .rodata : { *(.rodata .rodata.* .gnu.linkonce.r*) }
+    PROVIDE(_data = .);
+    .data : { *(.data .data.* .gnu.linkonce.d*) }
+    .bss (NOLOAD) : {
+        . = ALIGN(16);
+        __bss_start = .;
+        *(.bss .bss.*)
+        *(COMMON)
+        __bss_end = .;
+    }
+    _end = .;
+
+   /DISCARD/ : { *(.comment) *(.gnu*) *(.note*) *(.eh_frame*) }
+}
+__bss_size = (__bss_end - __bss_start)>>3;

rpi5-blink/Makefile

@@ -0,0 +1,28 @@
+SWIFT_EXEC ?= $(shell if [ "$(shell uname)" = "Darwin" ]; then xcrun -f swift; else which swift; fi)
+CLANG ?= $(shell if [ "$(shell uname)" = "Darwin" ]; then xcrun -f clang; else which clang; fi)
+LLVM_OBJCOPY ?= $(shell if [ "$(shell uname)" = "Darwin" ]; then xcrun -f llvm-objcopy; else which llvm-objcopy; fi)
+
+BUILDROOT := $(shell $(SWIFT_EXEC) build --triple aarch64-none-none-elf -Xswiftc -Xfrontend -Xswiftc -disable-stack-protector --show-bin-path)
+
+.PHONY: all clean
+
+all: kernel8.img
+
+kernel8.img: kernel8.elf
+	@echo "💾 Converting to binary kernel image with llvm-objcopy..."
+	$(LLVM_OBJCOPY) -O binary kernel8.elf kernel8.img
+	@echo ""
+	@echo "🥳 Done! kernel8.img was saved to this directory."
+
+kernel8.elf: $(BUILDROOT)/libMainApp.a $(BUILDROOT)/Support.build/boot.S.o link.ld
+	@echo "🔗 Linking with clang..."
+	$(CLANG) --target=aarch64-elf -o kernel8.elf $< $^ -fuse-ld=lld -nostdlib -Wl,--unresolved-symbols=ignore-in-object-files -Wl,-T ./link.ld
+	@echo ""
+
+$(BUILDROOT)/libMainApp.a $(BUILDROOT)/Support.build/boot.S.o: 
+	@echo "🛠️  Building with Swift Package Manager..."
+	$(SWIFT_EXEC) build --triple aarch64-none-none-elf -Xswiftc -Xfrontend -Xswiftc -disable-stack-protector
+	@echo ""
+
+clean:
+	rm -rf kernel8.elf kernel8.img .build

rpi5-blink/Package.resolved

@@ -0,0 +1,33 @@
+{
+  "originHash" : "193ca3f107e2c8dd2da5d091f6259f64b2cbfd6776d1c26bbcfb195b3a0b5045",
+  "pins" : [
+    {
+      "identity" : "swift-argument-parser",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/apple/swift-argument-parser.git",
+      "state" : {
+        "revision" : "41982a3656a71c768319979febd796c6fd111d5c",
+        "version" : "1.5.0"
+      }
+    },
+    {
+      "identity" : "swift-mmio",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/apple/swift-mmio.git",
+      "state" : {
+        "branch" : "swift-embedded-examples",
+        "revision" : "06d96ed4916739f2edafde87f3951b2d2a04df65"
+      }
+    },
+    {
+      "identity" : "swift-syntax",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/swiftlang/swift-syntax.git",
+      "state" : {
+        "revision" : "0687f71944021d616d34d922343dcef086855920",
+        "version" : "600.0.1"
+      }
+    }
+  ],
+  "version" : 3
+}

rpi5-blink/Package.swift

@@ -0,0 +1,36 @@
+// swift-tools-version: 6.1
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+  name: "RPi5-Blink",
+  platforms: [
+    .macOS(.v14)
+  ],
+  products: [
+    .library(
+      name: "MainApp",
+      type: .static,
+      targets: ["MainApp"])
+  ],
+  dependencies: [
+    .package(
+      url: "https://github.com/apple/swift-mmio.git",
+      branch: "swift-embedded-examples")
+  ],
+  targets: [
+    .target(
+      name: "MainApp",
+      dependencies: [
+        .product(name: "MMIO", package: "swift-mmio")
+      ],
+      swiftSettings: [
+        .enableExperimentalFeature("Embedded"),
+        .unsafeFlags(["-Xfrontend", "-function-sections"]),
+      ]
+    ),
+    .target(name: "Support"),
+
+  ]
+)