It is possible to calibrate the Internal Oscillator of a target AVR microcontroller using three independent 'Programming Projects' which are chained together to make a seamless programming sequence as follows:

Project 1

• Programmer programs 'Calibration Firmware' into Target AVR Microcontroller
• Programmer ENABLES the EESAVE Fuse in the Target AVR Microcontroller. This makes sure that any coefficients saved in the EEPROM during the execution of  the 'Calibration Firmware' are retained when the chip is erased at the start of Project 3.

Project 2

• Programmer enables an accurate 32kHz Oscillator signal on the MOSI pin
• Programmer forces 'Calibration Firmware' to execute on the real Target System by asserting the RESET pin accordingly
• Target AVR microcontroller performs the Calibration Function
• Target AVR microcontroller then writes the 'Calibration Coefficient(s)' into its own EEPROM memory
• Programmer detects when Calibration Firmware has finished and halts the execution of the firmware
• Programmer disables the 32kHz Oscillator signal on the MOSI pin

Project 3

• Programmer performs a Chip Erase operation on the Target AVR Microcontroller.
• The EEPROM area is NOT erased as the 'EESAVE' fuse was enabled in Project 1.
• Programmer writes the 'Production Firmware' to the Target AVR Microcontroller.
• Programmer writes the Security Fuses of the Target device.

Target AVR Microcontroller
This is the chip which requires to have its Internal Oscillator calibrated.
To use this procedure with the programmer in Stanalone Mode, the Target AVR Microcontroller must have an EESAVE fuse.

Calibration Firmware
This is a specially written application which executes on the Target AVR Microcontroller and which performs a 'Calibration Procedure' of the Internal RC Oscillator. The basic firmware is available from Atmel and is detailed in the Atmel Application Note AVR053 (see Downloads). You will then need to customise this firmware to your own Target AVR Microcontroller and Target System.

Production Firmware
This is the final 'application' firmware (software) which the microcontroller will be programmed with when the product leaves the factory.

Calcon Module
This is a specially designed I/O Connector Module which plugs into the PPM3-MK2 Programmer and produces the very accurate 32kHz square wave required for the Oscillator Calibration Process. See Associated Products for details. 

Hardware

• 1 x PPM3-MK2 Programmer
• 1 x CALCON Module

Software

• Calibration Firmware (see Atmel Application Note AVR053)
  - available from Atmel but will require customising to your target device and application.
• Equinox EQTools Software (comes with PPM3-MK2 programmer)

This procedure will only work if the target AVR Microcontroller has an 'EESAVE' fuse. If it does not have this fuse, then it is necessary to use the Equinox Script Builder software or ConsoleEDS Command Line utility to read the Calibration Coefficients out of the EEPROM to the PC and then write them back in again at the end of the programming sequence.