The user logic must hold usr_irq_req active-High
even after receiving usr_irq_ack (acks) to keep the
interrupt pending register asserted. This enables the Interrupt Service Routine (ISR)
within the driver to determine the source of the interrupt. Once the driver receives
user interrupts, the driver or software can reset the user interrupts source to which
hardware should respond by deasserting usr_irq_req.