I call a short and easy function out of an timer interrupt. This causes the c51 compiler to push all registers (A, B, DPH, DPL, PSW AR0..AR7) to the stack without any necessarity (they are not changed in this function). The fuction I call is in a seperate *.c file. How can I tell the C51-Compiler not to do this to save dataRAM and runtime? I can not use the using functionality because of register access.