On the Internet and in books, there are volumes of PIC sample code in assembly. How might one integrate such code into the structure of the FIRST code, and how would one call an assembly function from C (in mplab)?
There is some pretty good documentation on this at:
http://www.microchip.com/download/tools/picmicro/code/mplab18/51288b.pdf
see section 3.2.3