Optiboot flash is an easy to install bootloader for the Arduino environment. This repository contains a total of 9328 precompiled hex files built for 53 different targets with 14 different clock frequencies and 9 different baud rates to choose from.

• Small in size (<512 bytes when EEPROM upload support is disabled)
• Supports baudrates upto 1Mbit
• Supports write to flash within application
• Compatible with a most "classic" AVR microcontrollers
• EEPROM upload support
• Chips with 64kiB flash has flash page copy functionality, which is useful for a self-update application like ArduinoOTA

• ATmega640, ATmega1280, ATmega2560
• ATmega64, ATmega128, ATmega1281, ATmega2561
• AT90CAN32, AT90CAN64, AT90CAN128
• ATmega8535, ATmega16, ATmega32, ATmega164A/P, ATmega324A/P/PA/PB, ATmega644/P, ATmega1284/P
• ATmega8515, ATmega162
• ATmega8, ATmega88/P/PB, ATmega168/P/PB, ATmega328/P/PB
• ATmega169/P, ATmega329/P, ATmega649/P
• AT90USB646/647, AT90USB1286/1287
• ATmega325, ATmega645,
• ATmega3250, ATmega6450
• ATmega3290/P, ATmega6490/P

This repository contains a bunch of precompiled hex file with a variety of clock frequencies and baud rates:

The table below shows the available serial ports for the corresponding microcontroller. This repository contains precompiled hex files if you want to use other serial ports than UART0.

All precompiled binaries have an active LED output pin. The LED flashes twice when a hardware reset occurs. The table below shows which pin used used to drive the LED for a particular target:

You need to have make installed. You also need avr-libc, avr-binutils and avr-gcc. Alternatively you can install Arduino IDE, which comes with all these packages except make. Install Arduino IDE 1.8.9 or newer to be able to build for the new ATmega324PB and ATmega328PB.

To execute the build script you can either cd into the optiboot_flash folder and run make, or you can execute the script directly by running ./makeall.
If you just want to build a single file for a single target you can instead execute a make command formatted like this:

make atmega8 AVR_FREQ=16000000L BAUD_RATE=115200 LED=B5 LED_START_FLASHES=2 UART=0

Although it has evolved considerably, Optiboot builds on the original work of Jason P. Kyle (stk500boot.c),
Arduino group (bootloader), Spiff (1K bootloader), AVR-Libc group and Ladyada (Adaboot).

Optiboot is the work of Peter Knight (aka Cathedrow). Despite some misattributions, it is not sponsored or supported by any organisation or company including Tinker London, Tinker.it! and Arduino.
Maintenance of optiboot was taken over by Bill Westfield (aka WestfW) in 2011.
Flash write functionality added by majekw in 2015.