Hello
The problem with interrupt function is that they are not explicitly called in the application. So if you do not specify them in a FORCEACTIVE command they may not be linked with the application.
Usually one would create a constant table of function pointer for the interrupt table and then specify the table in the FORCEACTIVE command. This would make sure that all interrupt functions, which address is specified in the table gets linked to the application.
The statement .equ vec_base 0x3FE000 is probably stored somewhere in an assembly source file.
It associates the value 0x3FE000.to symbol vec_base.
So each time you will use vec_base in your assembly source file, assembler will replace that with 0x3FE000.
CrasyCat