Embedded Systems

Draft supports bare-metal and RTOS-based embedded development with no runtime overhead.

Overview

Draft’s no-GC, no-runtime design makes it ideal for resource-constrained environments.

Supported Platforms

Platform	Architecture	Min RAM	Min Flash
ARM Cortex-M	ARMv6-M/7-M/8-M	4 KB	16 KB
RISC-V	RV32IMAC	4 KB	16 KB
AVR	ATmega/ATtiny	1 KB	8 KB
ESP32	Xtensa	32 KB	128 KB
nRF52	ARM Cortex-M4	8 KB	32 KB

Getting Started

Install Embedded Target

draft target add arm-none-eabi
draft target add riscv32-unknown-none

Create Embedded Project

draft new my-embedded --template embedded
cd my-embedded

Project structure:

my-embedded/
├── draft.toml
├── memory.x          # Linker script
├── Cargo.toml        # (for HAL dependencies)
└── src/
    ├── main.draft
    └── interrupts.draft

Configuration

draft.toml

[package]
name = "my-embedded"
version = "0.1.0"

[target.thumbv7em-none-eabihf]
runner = "probe-run --chip STM32F407VG"

[profile.release]
opt-level = "s"      # Optimize for size
lto = true           # Link-time optimization

GPIO

Digital Output

import gpio

action main()
    @led = @gpio#Pin::new(13)
    @led#mode(@gpio#OUTPUT)

    while true
        @led#high()
        @time#sleep(milliseconds(500))
        @led#low()
        @time#sleep(milliseconds(500))
    fin while.
fin action.

Digital Input

import gpio

action main()
    @button = @gpio#Pin::new(0)
    @button#mode(@gpio#INPUT)
    @button#pull(@gpio#PULL_UP)

    while true
        if @button#read() == @gpio#LOW
            handle_press()
        fin if.
        @time#sleep(milliseconds(10))
    fin while.
fin action.

PWM

import gpio

action main()
    @pwm = @gpio#PWM::new(18)
    @pwm#frequency(1000)  @// 1 kHz

    for @duty in 0..100
        @pwm#duty(@duty)
        @time#sleep(milliseconds(20))
    fin for.
fin action.

Analog

ADC (Analog Input)

import adc

action main()
    @sensor = @adc#Channel::new(0)
    @sensor#resolution(12)  @// 12-bit

    while true
        @value = @sensor#read()
        @voltage = @value * 3.3 / 4095
        @time#sleep(milliseconds(100))
    fin while.
fin action.

DAC (Analog Output)

import dac

action main()
    @dac = @dac#Channel::new(1)

    for @value in 0..4095
        @dac#write(@value)
        @time#sleep(milliseconds(1))
    fin for.
fin action.

Communication Protocols

UART/Serial

import uart

action main()
    @serial = @uart#UART::new(0)
    @serial#baud(115200)
    @serial#tx_pin(0)
    @serial#rx_pin(1)

    @serial#write("Hello, World!\r\n")

    while true
        if @serial#available() > 0
            @data = @serial#read()
            @serial#write(@data)  @// Echo
        fin if.
    fin while.
fin action.

I2C

import i2c

action main()
    @bus = @i2c#I2C::new(0)
    @bus#sda_pin(4)
    @bus#scl_pin(5)
    @bus#frequency(400000)  @// 400 kHz

    @address = 0x68  @// MPU6050

    @// Read WHO_AM_I register
    @whoami = @bus#read_register(@address, 0x75)
    @io#write_line("WHO_AM_I: " + string(@whoami))

    @// Read accelerometer data
    @data = @bus#read_registers(@address, 0x3B, 6)
fin action.

SPI

import spi

action main()
    @bus = @spi#SPI::new(0)
    @bus#sck_pin(2)
    @bus#mosi_pin(3)
    @bus#miso_pin(4)
    @bus#frequency(1000000)  @// 1 MHz

    @cs = @gpio#Pin::new(5)
    @cs#mode(@gpio#OUTPUT)
    @cs#high()

    @// Read device ID
    @cs#low()
    @bus#transfer([0x9F])
    @id = @bus#transfer([0x00, 0x00, 0x00])
    @cs#high()
fin action.

CAN Bus

import can

action main()
    @bus = @can#CAN::new(0)
    @bus#baud(500000)  @// 500 kbps
    @bus#tx_pin(0)
    @bus#rx_pin(1)

    @msg = @can#Message::new(0x123)
    @msg#data([0x01, 0x02, 0x03, 0x04])
    @bus#send(@msg)

    while true
        @received = @bus#receive()
        if @received != nil
            process_message(@received)
        fin if.
    fin while.
fin action.

Timers

Hardware Timer

import timer

action main()
    @timer = @timer#Timer::new(0)
    @timer#frequency(1000)  @// 1 kHz
    @timer#callback(fn() =>
        toggle_led()
    fin action.)
    @timer#start()
fin action.

Watchdog

import watchdog

action main()
    @wd = @watchdog#Watchdog::new()
    @wd#timeout(seconds(1))
    @wd#start()

    while true
        @// Do work...
        @wd#pet()
    fin while.
fin action.

Interrupts

import gpio
import interrupts

action main()
    @button = @gpio#Pin::new(0)
    @button#mode(@gpio#INPUT)

    @interrupts#enable(@button, @interrupts#EDGE_FALLING, fn() =>
        handle_button_press()
    fin action.)

    while true
        @// Low power wait
        @power#wait_for_interrupt()
    fin while.
fin action.

Low Power Modes

import power

action main()
    while true
        @// Do work...
        @sensor_data = read_sensor()
        @radio#send(@sensor_data)

        @// Sleep for 10 seconds
        @power#sleep(seconds(10))
    fin while.
fin action.

Deep Sleep with Wake

import power
import gpio

action main()
    @wake_pin = @gpio#Pin::new(0)
    @wake_pin#mode(@gpio#INPUT)
    @wake_pin#wake_on(@gpio#EDGE_RISING)

    while true
        @// Enter deep sleep
        @power#deep_sleep()

        @// Woken up by interrupt
        handle_event()
    fin while.
fin action.

Memory Management

Static Allocation

@// Statically allocated buffer
@buffer: [Byte; 1024]

action main()
    for @i in 0..1024
        @buffer[@i] = 0
    fin for.
fin action.

Stack Allocation

action process()
    @// Allocated on stack
    @data: [Byte; 256]
    @// ...
fin action.

No Heap

By default, Draft embedded targets have no heap. All allocation is static or stack-based.

RTOS Integration

FreeRTOS

import freertos

action main()
    @rtos = @freertos#RTOS::new()

    @rtos#task("blink", fn() =>
        while true
            toggle_led()
            @rtos#delay(milliseconds(500))
        fin while.
    fin action.)

    @rtos#task("read_sensor", fn() =>
        while true
            @value = read_sensor()
            @rtos#queue_send("sensor_data", @value)
            @rtos#delay(milliseconds(100))
        fin while.
    fin action.)

    @rtos#start()
fin action.

Debugging

Semihosting

draft run --target thumbv7em-none-eabihf --semihosting

SWO Trace

draft debug --swo

GDB

draft debug --gdb

Flashing

@// Flash to device
draft flash --target thumbv7em-none-eabihf

@// Flash with probe
draft flash --probe cmsis-dap

@// Flash and run
draft run --target thumbv7em-none-eabihf

Size Optimization

[profile.release]
opt-level = "z"      # Optimize for size aggressively
lto = true
panic = "abort"

Typical sizes:

Application	Flash	RAM
Blink LED	2 KB	256 B
Sensor reader	8 KB	1 KB
Full stack	32 KB	8 KB