OHCI1394_IsoXmitIntEventClear
reg_write(ohci, OHCI1394_IsoXmitIntEventClear, 0xffffffff);
iso_event = reg_read(ohci, OHCI1394_IsoXmitIntEventClear);
reg_write(ohci, OHCI1394_IsoXmitIntEventClear, iso_event);
reg_write(ohci, OHCI1394_IsoXmitIntEventClear, 1 << index);