SIS_ISR
status = CSR_READ_4(sc, SIS_ISR);
status = CSR_READ_4(sc, SIS_ISR);
status = CSR_READ_4(sc, SIS_ISR);
CSR_READ_4(sc, SIS_ISR); /* clear any interrupts already pending */
status = CSR_READ_4(sc, SIS_ISR);