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avr-osccal

A C implementation of the OSCCAL algorithm in Atmel's App Note AVR053

Description

Atmel's AVR MCUs have internal oscillators that come factory-calibrated with a 10% tolerance. Applications using the internal oscillator and requiring an accurate clock should calculate a new calibration value given in-circuit voltage and temperature conditions.

App Note AVR053 describes a protocol for doing this automatically with the ISP interface. This is an implementation in C, for convenience and portability. It may be used in conjunction with either avrdude or atprogram (part of Atmel Studio) for the actual calibration.

For maximum portability, this implementation follows the recommendations of AVR053 in avoiding interrupts and using the 8-bit timer, which should allow it to run on any AVR device.

License

This code is under the BSD-2-Clause license.

Usage

Edit the constants at the top of the makefile. Then run:

make
make install
make calibrate

The calculated OSCCAL value will be stored in EEPROM at address 0x00. Note that the EESAVE fuse must be set, or it will be erased as soon as you flash your final code.

Your final code should then read EEPROM address 0x00 during startup and write it to OSCCAL.

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A C implementation of the OSCCAL algorithm in Atmel's App Note AVR053

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