Running Swift without an OS

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8IBUTSVOOJOHCFIJOEUIJT import SwiftUI // We start here @main struct MyApp: App { var body: some Scene { WindowGroup { ContentView() } } } 8IBU)BQQFOT#FIJOE!NBJO

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&WFSZUIJOHJTBNFNPSZSFBEPSXSJUF "MMDPOUSPMMFEUISPVHINFNPSZ CPU Read Write Memory

.FNPSZ.BQQFE*0 "MMDPOUSPMMFEUISPVHINFNPSZ >_ OLED

0x1000_0000 Flash Code, Boot2, Vector Table 0x2000_0000 RAM Variables, Stack
0x4000_0000 Peripherals 0xD000_0000 SIO 0xE000_0000 System UART Serial I2C Display PWM Sound, LED GPIO LED on/off SysTick Timer .FNPSZ.BQQFE*0 "MMDPOUSPMMFEUISPVHINFNPSZ >_ OLED

0x1000_0000 Flash Code, Boot2, Vector Table 0x2000_0000 RAM Variables, Stack
0x4000_0000 Peripherals 0xD000_0000 SIO 0xE000_0000 System UART Serial I2C Display PWM Sound, LED GPIO LED on/off SysTick Timer .FNPSZ.BQQFE*0 "MMDPOUSPMMFEUISPVHINFNPSZ >_ OLED CPU

.FNPSZ.BQQFE*0 4BNFNFDIBOJTNPOGVMM04 BMMEFWJDFJTKVTUBOBEESFTT iOS / macOS Your App UIKit /
SwiftUI / Foundation macOS / iOS Kernel Device Drivers Memory-Mapped I/O Bare Metal Your App No frameworks No OS No drivers Memory-Mapped I/O Display Network Storage Audio Sensors

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3FTFU)BOEMFS .FNPSZJOJUJBMJ[BUJPO "QQMJDBUJPONBJO 4XJGUXPSMECFHJOTIFSF Flash (ROM) 0x1000_0000 .boot2 0x1000_0100 .vector .text ...

)PX4XJGU1MBDFT$PEFBU'JYFE"EESFTTFT !TFDUJPO !VTFE BOE!D @section(".boot2") // ← place at fixed
address @used // ← don't optimize away let boot2: (...) = (0xB3, 0x21, ...) @section(".vector") // ← place at fixed address @used // ← don't optimize away let vectorTable: ( UInt32, // [0] Initial stack pointer @convention(c) () -> Void, // [1] Reset handler ... ) = ( 0x2004_0000, // Top of RAM resetHandler, // First function to call ... )

)PX4XJGU1MBDFT$PEFBU'JYFE"EESFTTFT !TFDUJPO !VTFE BOE!D Main.swift Board.swift Startup.swift Source Files Compiler
swiftc .o Main.o Board.o Startup.o Object Files (addresses not yet assigned) Linker ld memmap.ld Linker Script 01 10 .boot2 .text code + vector table .data .bss Binary (firmware.uf2) (addresses assigned)

)PX4XJGU1MBDFT$PEFBU'JYFE"EESFTTFT !TFDUJPO !VTFE BOE!D @section(".boot2") // ← place at fixed
address @used // ← don't optimize away let boot2: (...) = (0xB3, 0x21, ...) @section(".vector") // ← place at fixed address @used // ← don't optimize away let vectorTable: ( UInt32, // [0] Initial stack pointer @convention(c) () -> Void, // [1] Reset handler ... ) = ( 0x2004_0000, // Top of RAM resetHandler, // First function to call ... )

)PX4XJGU1MBDFT$PEFBU'JYFE"EESFTTFT !TFDUJPO !VTFE BOE!D let vectorTable: ( UInt32, // [0]
Initial stack pointer @convention(c) () -> Void, // [1] Reset handler ... ) = ( 0x2004_0000, // Top of RAM resetHandler, // First function to call ... ) @c // ← C calling convention func resetHandler() { ... }

MEMORY { ROM(rx) : ORIGIN = 0x10000000, LENGTH = 2048k
RAM(rwx) : ORIGIN = 0x20000000, LENGTH = 256k } SECTIONS { .boot2 : { KEEP(*(.boot2)) } > ROM .text : { *(.vector) *(.text*) } > ROM ... } -JOLFS4DSJQU 8IFSF4FDUJPOT(P

RAM(rwx) : ORIGIN = 0x20000000, LENGTH = 256k } SECTIONS { .boot2 : { KEEP(*(.boot2)) } > ROM .text : { *(.vector) *(.text*) } > ROM ... } -JOLFS4DSJQU 8IFSF4FDUJPOT(P Flash (ROM) RAM

RAM(rwx) : ORIGIN = 0x20000000, LENGTH = 256k } SECTIONS { .boot2 : { KEEP(*(.boot2)) } > ROM .text : { *(.vector) *(.text*) } > ROM ... } -JOLFS4DSJQU 8IFSF4FDUJPOT(P Flash (ROM) RAM @section(".boot2") @section(".vector")

8IBUUIF7FDUPS5BCMF4FUT6Q 4UBDL1PJOUFS3FTFU)BOEMFS Flash (ROM) Boot2 Vector Table [0] Stack Pointer
[1] Reset Handler .text (code) .data (initial values) ... RAM .data .bss (free) Stack

[1] Reset Handler .text (code) .data (initial values) ... RAM .data .bss (free) Stack <>4FUVQUIFTUBDL

[1] Reset Handler .text (code) .data (initial values) ... RAM .data .bss (free) Stack <>4FUVQUIFTUBDL <>$BMMTSFTFUIBOEMFS

@c func resetHandler() { Application.main() // ← You call main()
yourself } @main struct Application { static func main() { // Your application code starts here } } 'JOBMMZ NBJO /PPOFDBMMTJUGPSZPV

@c func resetHandler() { Application.main() } @main struct Application {
static func main() { // Unreset IO_BANK0 Register(address: 0x4000_C000).clear(1 << 5) while Register(address: 0x4000_C008).load() & (1 << 5) == 0 {} // Configure GPIO25 (on-board LED) Register(address: 0x4001_4000 + 0x04 + 25 * 8).store(5) Register(address: 0xD000_0024).store(1 << 25) Register(address: 0xD000_001C).store(1 << 25) // Flip the bit to turn on while true { for _ in 0..<500_000 { _ = Register(address: 0xD000_0000).load() // Delay } Register(address: 0xD000_001C).store(1 << 25) // Flip the bit to toggle } } }

import _Volatile struct Register { let address: UInt32 /// Reads
the register value. @inline(__always) func load() -> UInt32 { VolatileMappedRegister<UInt32>(unsafeBitPattern: UInt(address)).load() } /// Writes a value to the register. @inline(__always) func store(_ value: UInt32) { VolatileMappedRegister<UInt32>(unsafeBitPattern: UInt(address)).store(value) } ... }

static func main() { // Unreset IO_BANK0 Register(address: 0x4000_C000).clear(1 << 5) while Register(address: 0x4000_C008).load() & (1 << 5) == 0 {} // Configure GPIO25 (on-board LED) Register(address: 0x4001_4000 + 0x04 + 25 * 8).store(5) Register(address: 0xD000_0024).store(1 << 25) Register(address: 0xD000_001C).store(1 << 25) // Flip the bit to turn on while true { for _ in 0..<500_000 { _ = Register(address: 0xD000_0000).load() // Delay } Register(address: 0xD000_001C).store(1 << 25) // Flip the bit to toggle } } }

static func main() { // Unreset IO_BANK0 Register(address: resetsReset).clear(1 << ioBank0) while Register(address: resetsDone).load() & (1 << ioBank0) == 0 {} // Configure GPIO25 (on-board LED) Register(address: ioBankBase + ctrlOffset + ledPin * pinStride).store(funcSIO) Register(address: sioOutputEnableSet).store(1 << ledPin) Register(address: sioOutputXor).store(1 << ledPin) // Flip the bit to turn on while true { for _ in 0..<500_000 { _ = Register(address: sioBase).load() // Delay } Register(address: sioOutputXor).store(1 << ledPin) // Flip the bit to toggle } } }

.FNPSZ4FDUJPO*OJUJBMJ[BUJPO .BLJOHHMPCBMTUBUJDWBSJBCMFTVTBCMF static let sioBase: UInt32 = 0xD000_0000 // non-zero
initial value static let ledPin: UInt32 = 25 // non-zero initial value static var counter: UInt32 = 0 // zero initial value static var name: String? // nil = zero in memory ROM (Flash) .text (code) .data 0xD000_0000 25 ... .bss (size info only, no data stored) counter, name, ... ...

.FNPSZ4FDUJPO*OJUJBMJ[BUJPO .BLJOHHMPCBMTUBUJDWBSJBCMFTVTBCMF UInt32 = 0xD000_0000 e Int32 = 25 e
UInt32 = 0 ing? ROM (Flash) .text (code) .data 0xD000_0000 25 ... .bss (size info only, no data stored) counter, name, ... ... RAM .data (variables) .bss (zero-filled) ...

.FNPSZ4FDUJPO*OJUJBMJ[BUJPO .BLJOHHMPCBMTUBUJDWBSJBCMFTVTBCMF Startup.swift @_extern(c, "__data_start") var __data_start: UInt8 @_extern(c, "__data_end")
var __data_end: UInt8 @_extern(c, "__bss_end") var __bss_end: UInt8 // Linker symbols → RAM addresses RAM .data (variables) __data_start __data_end .bss (zero-filled) __bss_end ...

func initializeMemorySections() { ... // Copy initial values from ROM
to RAM var src = dataOrigin var dst = dataStart while dst != dataEnd { dst.pointee = src.pointee dst = dst.advanced(by: 1) src = src.advanced(by: 1) } // Zero out the rest while dst != bssEnd { dst.pointee = 0 dst = dst.advanced(by: 1) } } JOJUJBMJ[F.FNPSZ4FDUJPOT $PQZBOE[FSP fi MM

func initializeMemorySections() { ... // Copy initial values from ROM
to RAM var src = dataOrigin var dst = dataStart while dst != dataEnd { dst.pointee = src.pointee dst = dst.advanced(by: 1) src = src.advanced(by: 1) } // Zero out the rest while dst != bssEnd { dst.pointee = 0 dst = dst.advanced(by: 1) } } JOJUJBMJ[F.FNPSZ4FDUJPOT $PQZBOE[FSP fi MM @_extern(c, "__data_origin") var __data_origin: UInt8 @_extern(c, "__data_start") var __data_start: UInt8 @_extern(c, "__data_end") var __data_end: UInt8 @_extern(c, "__bss_end") var __bss_end: UInt8

3FBEZUP3VO .FNPSZJOJUJBMJ[FE NBJO DBOTUBSU @c func resetHandler() { initializeMemorySections() //
← Initialize memory Application.main() // ← Now constants work } @main struct Application { static func main() { // Unreset IO_BANK0 Register(address: resetsReset).clear(1 << ioBank0) while Register(address: resetsDone).load() & (1 << ioBank0) == 0 {} // Configure GPIO25 (on-board LED) Register(address: ioBankBase + ctrlOffset + ledPin * pinStride).store(funcSIO) Register(address: sioOutputEnableSet).store(1 << ledPin) ... } }

@c func resetHandler() { initializeMemorySections() // ← Initialize memory Application.main()
// ← Now constants work } @main struct Application { static func main() { // Unreset IO_BANK0 Register(address: resetsReset).clear(1 << ioBank0) while Register(address: resetsDone).load() & (1 << ioBank0) == 0 {} // Configure GPIO25 (on-board LED) Register(address: ioBankBase + ctrlOffset + ledPin * pinStride).store(funcSIO) Register(address: sioOutputEnableSet).store(1 << ledPin) ... } } 3FBEZUP3VO .FNPSZJOJUJBMJ[FE NBJO DBOTUBSU

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static func main() { var board = Board() // Initialize
clocks, GPIO, USB while true { let gpioState = board.buttons.poll() // Poll button states board.usb.poll() // Handle USB events if board.usb.configured { board.usb.sendXInputReport( // Send button states to host gpioState: gpioState ) } } } 4VQFS-PPQ 64#(BNF$POUSPMMFS

$PPQFSBUJWF4DIFEVMFS 3FHJTUFSJOHBOE3VOOJOH5BTLT SCORE 01240 gameState fallInterval inputDebounce lineClearing musicPosition renderBuffer
score / level buttonEdge pieceRotation softDropTimer animPhase noteFrequency i2cTransfer pwmDutyCycle ...

func taskGameLogic() { ... } func taskRender() { board.display.clear() renderBoard()
renderPiece() board.display.flush() // I2C transfer (heavy) } func taskMusic() { Music.advance() // Play next note } static func main() { var scheduler = Scheduler() scheduler.addTask(interval: 16, taskGameLogic) scheduler.addTask(interval: 16, taskRender) scheduler.addTask(interval: 8, taskMusic) scheduler.run() // → Never (doesn't return) } $PPQFSBUJWF4DIFEVMFS 3FHJTUFSJOHBOE3VOOJOH5BTLT

$PPQFSBUJWF4DIFEVMFS 5BTLTDBOOPUCFJOUFSSVQUFE 0ms 8ms 40ms Music Game Logic Render (I2C
display transfer) Button Input Music Music Button Input %FMBZFE %FMBZFE

)ZCSJE"QQSPBDI 4DIFEVMFS *OUFSSVQUT Scheduler Interrupts 0ms 16ms 32ms Game Logic
Render (I2C display) Game Logic Render Music Music Music Music Music Music Button Input Scheduler tasks Music (timer interrupt) Button Input (GPIO interrupt)

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Running Swift without an OS

Running Swift without an OS

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