RTK_ISR
status = CSR_READ_2(sc, RTK_ISR);
CSR_WRITE_2(sc, RTK_ISR, status);
CSR_WRITE_2(sc, RTK_ISR, 0xFFFF);
CSR_WRITE_2(sc, RTK_ISR, 0xFFFF);
status = CSR_READ_2(sc, RTK_ISR);
status = CSR_READ_2(sc, RTK_ISR);
CSR_WRITE_2(sc, RTK_ISR, status);