When I look at the libpololu-avr directory created by downloading and unzipping the appropriate file from the pololu website, under “devices” I see 2 folders: atmega1284p and atmega1284p_x2. Which one of these folders should I use if I am working with the Orangutan svp-1284 controller? What is the difference between atmega1284p and atmega1284p_x2?
For the Orangutan SVP-1284, you should use the atmega1284p folder. The “_x2” stands for the Orangutan X2.
The difference between those two folders is that they correspond to two different versions of the library, the atmega1284p version and the atmega1284p_x2 version. The atmega1284p version was made first and it supports the Orangutan SVP-1284. The atmega1284p_x2 version was made later and it supports the newer Orangutan X2s with the ATmega1284P.