What you just got is a linker error. Linker errors generally talk about variables or functions that are not found anywhere and are often cryptic. Usually your best way to solve them is to use the "Find in project files..." option and search for the variable or function in question and find out how they are used.
Usually they result from typos or missing files. If you see a warning like "Implicit definition of function" then that means that you do not have a "header" file with the fuction delcared in it. This often results in such linker errors.
In this case, just declare an int variable called "Old_Port_B" at the top of interrupts.c so that the linker will find it.
Just make sure that you declare it outside of a function because the linker does not look in local variables.
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-Patrick Horn,
Paly Robotics
Check out the space simulator called
Vega Strike, modelled after the space simulator games Elite and Wing Commander. It's Open Source too!
If you have ever played
Wing Commander, or especially
Privateer, and had a feeling of nostalga derived from the you will enjoy these two Vega Strike mods:
Privateer Gemini Gold and
Privateer Remake!
I'm working on adding multiplayer support this year...