Hi! First of all: Thank you a lot for having fixed the "swi" instruction! No more "unknown swi xxx". I have stepped through all the code from my swi_wrapper and swi_handler and it worked very nice! :-) :-) I think, I have found the little bug in the arm simulator. It is only one line in "armsupp.c", function ARMul_FicCPSR: void ARMul_FixCPSR (ARMul_State * state, ARMword instr, ARMword rhs) { state->Cpsr = ARMul_GetCPSR (state); /* original src */ /* if (state->Bank != USERBANK) */ // buggy /* end original src */ /* altered src */ if (state->Mode != USER32MODE) /* end altered src */ { /* In user mode, only write flags */ if (BIT (16)) SETPSR_C (state->Cpsr, rhs); if (BIT (17)) SETPSR_X (state->Cpsr, rhs); if (BIT (18)) SETPSR_S (state->Cpsr, rhs); } if (BIT (19)) SETPSR_F (state->Cpsr, rhs); ARMul_CPSRAltered (state); } The original version tried to determine the cpu state by the banked registers. This works most time, but not if we are in system mode. System and user mode have same banked registers. That why msr cpsr, r0 worked for all modes but not for system mode. I don´t know, how to care about the case we are in USER26MODE, it could be done with some "defines" I would suppose. I hope this little fix does not have any side effects! Regards, Jens-Christian -- Jens-Christian Lache www.tu-harburg.de/~sejl1601 lache@tu-harburg.de Tel.: 01759610756 (Hamburg)