JSON file for ATtinyCore with micronucleus bootloader and LTO support

A project log for ATtiny84a tiniest development board

A development board for the ATtiny84a which can be used on a bread board. Just all the basics to run the micronucleus bootloader.

Sander van de BorSander van de Bor 02/26/2019 at 03:253 Comments

The JSON file is finished and can be used to update the Arduino boards manager. Add the following link to the Additional Boards Manager URLs in Preferences of the Arduino IDE:

Next go to the Boards Manager under Tools and search for ATtiny. You should get a result with ATtinyCore boards with

micronucleus by California STEAM. Click on install to install these boards.

It will download the ATtiny Core 1.2.2 from Spence Konde and Micronucleus 2.0a4 from Digistump. After a successful install you will find the new boards under Tools -> Boards.

You can use LTO during compiling to reduce your sketch with about 10% (depending on the sketch). Activate LTO by going to Tools ->  LTO -> Enabled.


Space Buck wrote 06/04/2019 at 23:35 point

I'm unclear what to do once the board is installed. I have an ATTiny84 wired up as if I were burning the regular ATTinyCore bootloader...what then? If I choose "ATtiny84 (California STEAM)", and then click "Burn Bootloader", I get the error message "The current selected board needs the core 'ATTinyCore:tiny' that is not installed."

I'm certain I have ATTinyCore installed on my computer, so what am I doing wrong?

  Are you sure? yes | no

Sander van de Bor wrote 06/05/2019 at 00:07 point

Hi! Are you using the California STEAM development board, or are you trying to burn a custom board with the bootloader? I haven't setup the board variation to upload bootloaders, I usually do it from command prompt with AVRDUDE. All the California STEAM boards already ship with the bootloader installed, and so is the Digispark.

I use the following micronucleus bootloaders for the ATtiny84a:

From the command prompt I run AVRDUDE, located in

C:\Program Files (x86)\Arduino\hardware\tools\avr\bin

with the following command:

avrdude -CC:\Users\svandebor\AppData\Local\Arduino15\packages\ATTinyCore\hardware\avr\1.2.3/avrdude.conf -v -pattiny84 -carduino -PCOM4 -b19200 -Uflash:w:C:\Users\svandebor\Documents\t84_default.hex:i  -U lfuse:w:0xe2:m -U hfuse:w:0xdd:m -U efuse:w:0xfe:m

Please let me know if this helps for you.

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Space Buck wrote 06/05/2019 at 06:07 point

Ah, my mistake. I am using a bare ATtiny84. Thanks for the suggestions for manually burning the bootloader!

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