How to build AVR code for the Digispark with PlatformIO

PlatformIO supports the Digispark USB development board, a compact board with the ATtiny85 AVR microcontroller. The canonical example code that lets the built-in LED blink looks like this:

digispark_blink_platformio/main.c (Source)

/* Atml AVR native blink example for the Digispark
 * Copyright (C) 2021 Koen Vervloesem (
 * SPDX-License-Identifier: MIT
#include <avr/io.h>
#include <util/delay.h>

// Digispark built-in LED
// Note: on some models the LED is connected to PB0
#define PIN_LED PB1
#define DELAY_MS 1000

int main(void) {
  // Initalize LED pin as output
  DDRB |= (1 << PIN_LED);

  while (1) {
    PORTB ^= (1 << PIN_LED);

  return 0;


This doesn't use the Arduino framework, but directly uses the native AVR registers.

If you've bought your Digispark recently, the Micronucleus bootloader is a recent version that isn't supported by PlatformIO's older micronucleus command.

If you've already upgraded the bootloader on your Digispark, you also have the newest version of the micronucleus command. So the only thing you need is make PlatformIO use this version when uploading your code. You can do this with the following platformio.ini:

platform = atmelavr
board = digispark-tiny
upload_protocol = custom
upload_command = micronucleus --run .pio/build/digispark-tiny/firmware.hex

The platform and board options are just the configuration options the PlatformIO documentation lists for the Digispark USB. By setting the upload_protocol to custom, you can supply your own upload command, and the micronucleus in this command refers to the one you've installed globally with sudo make install in /usr/local/bin/micronucleus.

After this, you can just build the code and upload it:

koan@tux:~/digispark_blink_platformio$ pio run -t upload
Processing digispark-tiny (platform: atmelavr; board: digispark-tiny)
Verbose mode can be enabled via `-v, --verbose` option
PLATFORM: Atmel AVR (3.1.0) > Digispark USB
HARDWARE: ATTINY85 16MHz, 512B RAM, 5.87KB Flash
DEBUG: Current (simavr) On-board (simavr)
 - tool-avrdude 1.60300.200527 (6.3.0)
 - toolchain-atmelavr 1.50400.190710 (5.4.0)
LDF: Library Dependency Finder ->
LDF Modes: Finder ~ chain, Compatibility ~ soft
Found 0 compatible libraries
Scanning dependencies...
No dependencies
Building in release mode
Checking size .pio/build/digispark-tiny/firmware.elf
Advanced Memory Usage is available via "PlatformIO Home > Project Inspect"
RAM:   [          ]   0.0% (used 0 bytes from 512 bytes)
Flash: [          ]   1.4% (used 82 bytes from 6012 bytes)
Configuring upload protocol...
CURRENT: upload_protocol = custom
Uploading .pio/build/digispark-tiny/firmware.hex
> Please plug in the device ...
> Device is found!
connecting: 33% complete
> Device has firmware version 2.5
> Device signature: 0x1e930b
> Available space for user applications: 6650 bytes
> Suggested sleep time between sending pages: 7ms
> Whole page count: 104  page size: 64
> Erase function sleep duration: 728ms
parsing: 50% complete
> Erasing the memory ...
erasing: 66% complete
> Starting to upload ...
writing: 83% complete
> Starting the user app ...
running: 100% complete
>> Micronucleus done. Thank you!
====================================== [SUCCESS] Took 3.99 seconds ======================================

I've created a GitHub project with this configuration, the example code, a Makefile and a GitHub Action to automatically check and build the code: koenvervloesem/digispark_blink_platformio. This can be used as a template for your own AVR code for the Digispark with PlatformIO.