diff --git a/arch/armv7/nvic.h b/arch/armv7/nvic.h
index bb7bb159b79383622c812f0405119326b443b3a6..201adf5c3acee193b6fdf2f453095137361dc8b3 100644
--- a/arch/armv7/nvic.h
+++ b/arch/armv7/nvic.h
@@ -110,6 +110,11 @@ namespace arch {
          * @brief Saves the register before entering a isr
          */
         static void forceinline save_register() {
+            /*
+             * generates as function pro- and epilogue:
+             * stmdb   sp!, {r4, r5, r6, r7, r8, r9, sl, fp, lr}
+             * ldmia.w sp!, {r4, r5, r6, r7, r8, r9, sl, fp, pc}
+             */
             asm volatile("nop":: :"r4", "r5", "r6", "r7", "r8", "r9", "r10", "r11", "r12", "lr");
         }