I just noticed that the lib str710 doesn't re enable IRQ in the irq handler : IRQ_to_SYS MACRO MSR cpsr_c,#0x1F ; Switch to SYS mode STMFD sp!,{lr} ; Save the link register. ENDM The 1F mode is the system and user mode but nothing re-enable the interrupts. Is there a good reason for this? Is it possible to re-enable interrupt that way : MSR cpsr_c,#0x1F |I_Bit |F_Bit ; Switch to SYS mode I think yes because the EIC component manage priority. Isn't it. Thanks, Ludo