Hello,I'm using the soft-core Cortex-M0,keil uvision 5,vivado 14.4 i interfaced an adder with my arm architecture first,i used the assembly language, the simulation in vivado simulator worked correctly. my first assembly code---> -------------------------------------------- Reset_Handler PROC GLOBAL Reset_Handler ENTRY LDR R1,=0x59000000 LDR R0,=0x33 STR R0,[R1] ------------------------------------------- Now, i want to use C nd Assembly language but simulation doesn't work, it can't access to the adder registers the second assembly--> ---------------------------------------------------- Reset_Handler PROC GLOBAL Reset_Handler ENTRY IMPORT __main LDR R0, =__main BX R0 ENDP --------------------------------------------------------- the C code--> ----------------------------------------------------------- #define AAA 0x59000000 int main(void) { *(unsigned int*)AAA=0x44 ; } -------------------------------------------------------- i can't know what's my fault