The http://www.nongnu.org/simulavr/%|%SimulAVR%|% program is a simulator for the Atmel AVR family of microcontrollers. (ATtiny and ATmega) SimulAVR can be used either standalone or as a remote target for avr-gdb. There is a python- and Tcl interface. 

See also [Arduino] for an (eco-)system making heavy use of the AVR controller family.

See also http://reprap.org/wiki/SimulAVR#TCL_Examples

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