The user's manual & technical manual have VOCOL documentation. I've only skimmed it, though.

http://www.robotu.com/Gemini_files/User_Manual.pdf starting on page 55

http://www.robotu.com/Gemini_files/Tech_Reference.pdf starting on page 47

I suspect roms/VOCREM.BIN in the 'software' package is actually the compiled VOCOL code, but I haven't disassembled it to find out yet.