On Mon, Jun 10, 2013 at 5:41 PM, Kalai Rajah N <kalairajah@xxxxxxxxx> wrote: > "ldr r1, =%0 /* load the nvic_iser* register */ \n\t" The references are coming from your lines like the above. I don't know what this syntax means. You are asking GCC to put a register name in there, so the result is something like ldr r1, =r1 This winds up referring to a symbol named r1, rather than the register r1. Ian