The IRL interrupt is a level sense interrupt, and it is not retained in SH-4. Therefore it is possible to fail to take the interrupt under following condtions (a) or (b) during the IRL interrupt is input.
When it is the IRL interrupt, please assert the IRL interrupt signals until the interrupt request is accespted and withdraw the interrupt request (Inputting to IRL pins are negated) in the corresponding interrupt handler.
(a) SR.BL bit is set to 1.
(b) The interrupt priority level from IRL pins is lower than the level of SR.IMASK bit.