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AVR ATmega port of freeRTOS

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AVR ATmega port of freeRTOS A port of freeRTOS which can be flexibly flexibly configured use almost any available Timer on AVR ATmega devices and will operate with almost any classic Arduino device from Arduino, SeeedStudio, Sparkfun, Freetronics or Pololu.

The Goldilocks Analogue story of adding a dual channel DAC to a 1284p classic Arduino board is told here. The Goldilocks Analogue - Kickstarter Campaign was successfully funded. It was also a Hackaday Prize 2015 Quarter Finalist.

Goldilocks Analogue

The first Goldilocks 1284p story is here. Ths idea was launched as a Pozible campaign in 2013. It was successfully funded and the Goldilocks was developed and supported by Freetronics.

This repo has been hosted on Sourceforge avrfreertos since 2011, and has been downloaded over 25,000 times. Going forward Sourceforge will be updated less often and only with major releases.

Follow @_feilipu on Twitter.

Getting Started

To get started, follow the instructions on freeRTOS & libraries for AVR ATmega. Then do some further reading on the freeRTOS Quick Start Guide.

If this repository is too complicated to get started, a minimum AVR freeRTOS configured using the Watchdog Timer and Heap 3 is also also available. This option is without libraries, and is configured to get started with simple applications.

Also, for the Arduino platform, there is an Arduino freeRTOS Library available in the Arduino IDE Library manager, or by directly downloading the ZIP file and importing it into your Arduino IDE.


The freeRTOS scheduler can be driven by any of the AVR ATmega timers, down to one millisecond (or less) time slices, depending on the application requirements. By using Timer2 for scheduling timing can be linked with a RTC capability with up to millisecond accuracy. By using the Watchdog Timer for scheduling no externally useful system resources are consumed, but time slicing is limited to 15 millisecond increments. Generally, I use the freeRTOS scheduler for loose timing (15ms) and hardware timers for tight (microsecond) timing, but each application is different.

There are multiple options for configuring the heap in freeRTOS. Please read the freeRTOS descriptions for the appropriate solution relevant to the application. Heap versions 1, 2, 3, and 4 have been implemented for this repository.

An integrated RTC providing Standard C90 system_time using the 32.768kHz crystal attached to Timer2 on 1284p Goldilocks or other RTC equipped boards. Standard C90 system_time is also available as an approximate RTC off other timers using 16MHz and other crystals.

Further Reading

The canonical source for information is the freeRTOS Web Site. Within this site, the Getting Started page is very useful. It is worth having a view from another user, and manicbug has some interesting examples. This AVRfreeRTOS Repository has plenty of examples, ranging from Blink through to a Synthesiser for the Goldilocks Analogue.

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