Does anyone knows a methode, to declare a function in a specific CODE address in C51? Something lika a org xxxx in assembler !
What you're doing with your two functions is a combination of traditional C51 techniques "code banking" and "xdata banking". Neither would strictly need any knowledge about absolute memory locations for functions if you had let the C compiler help you doing it. If you insist doing it on your own, you'll have to investigate the suggestions you already got: put functions in separate segments, let the linker place those segments at fixed locations.