In this specific case it is a driver for a 7-segment, 8-digit max7219 display. Basically what you need to do is write in a header.h file the prototypes of the functions to be created, and, on a separate .c file they must be implemented. The file point c it has no main function because it is a file that is about to become a library. Here is the sequence of instructions to use:

• sdcc -c max7219a.c // which will produce the file max7219.rel
• sdar -rc max7219a.lib max7219a.rel //which will produce the library file
• sdcc Tester.c max7219a.lib // To use the library from Tester.c. The result is an .ihx file

Of all the files produced, the ones needed to reuse the library are the max7219a.h files, which will added in the header of the main program with the directive #include " max7219a.h", and the max7219a.lib file which contains the software defined in the max7219a.h.