WebbotLib AVR library
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atmega640.h

This is the system file you should include if you are developing for a generic ATMega640 board.
It will make sure that your compiler settings are appropriate: ie ATMega640 running at 16MHz.
This is the system file you should include as a matter of last resort if you are developing for the ATMega640 but your actual board is not listed in the sys folder. ie it is for a generic ATMega640 board. This may also be because you have created your own ATMega640 based board. Consequently the library assumes that all processor pins have header pins.
It will make sure that your compiler settings are appropriate: ie ATMega640

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