I/O Debug Register (IDR)

The OCD debugger makes use of the memory mapped OCDR register to access the internals of the Atmel AVR target device while it is in stopped mode. When in run mode, the application running on the target can write a value to this register. The OCD system will then signal this to the debugger, which then fetches the data and passes it to the GUI front-end, where it is displayed. The application can thus give primitive debug messages to the debugger.

Note: The IDR value is polled at a fixed interval (100ms) so writing to it at a higher frequency than this will not yield reliable results.
Note: If the AVR target device experiences a power out condition while it is being debugged, spurious IDR messages may result. This because the debugger continues to pull the AVR as the voltage drops below its minimum operating voltage.