The C51 compiler includes a number of source files you can modify to adapt your target program to a specific hardware platform. These files contain code that is executed on startup (STARTUP.A51), and code to perform low-level stream I/O (GETKEY.C and PUTCHAR.C). Source code for the memory allocation routines is also included in the files CALLOC.C, FREE.C, INIT_MEM.C, MALLOC.C, and REALLOC.C. All of these source files are described in detail in the following sections.
The code contained in these files is already compiled or assembled and included in the C library. When you link, the code from the library is automatically included.
If you want to include custom startup or initialization routines, you must include them in the project.