improve comment (#658)
diff --git a/src/rp2_common/hardware_irq/include/hardware/irq.h b/src/rp2_common/hardware_irq/include/hardware/irq.h
index 424a497..26183cd 100644
--- a/src/rp2_common/hardware_irq/include/hardware/irq.h
+++ b/src/rp2_common/hardware_irq/include/hardware/irq.h
@@ -258,6 +258,10 @@
/*! \brief Clear a specific interrupt on the executing core
* \ingroup hardware_irq
*
+ * This method is only useful for "software" IRQs that are not connected to hardware (i.e. IRQs 26-31)
+ * as the the NVIC always reflects the current state of the IRQ state of the hardware for hardware IRQs, and clearing
+ * of the IRQ state of the hardware is performed via the hardware's registers instead.
+ *
* \param int_num Interrupt number \ref interrupt_nums
*/
static inline void irq_clear(uint int_num) {
