Hey, I am trying to program a CORTEX A9 Processor with ARM and a GCC/GNU toolchain. At first the processor is in SVC-Mode then I want to switch to User-Mode and run a user-program. My first try is only to switch from SVC- to User-Mode and then calling a SWI to get back to SVC-Mode. Without changing to User-Mode everything with the SWI and the returns works well, but if I change to User-Mode everything breaks down. My questions are: Needs the program a User-Stack if I only switch to User-Mode and in the next step I call the SWI? Which registers must I save bevor switching to User-Mode? I added two files: One is the swiHandler.c and the other one called: beforeUserMode_test.s, switches to the User-Mode and then calls the SWI. I think I Need to save some pointer in this file and restore them at the right point again, but I do not know when I have to do this. I am new here and if you need more details to my problem please write what you need and i will post it. Thanks for helping me Andi