VR_ISR
CSR_WRITE_2(l, VR_ISR, ~0);
CSR_WRITE_4(l, VR_ISR, ~0);
CSR_WRITE_2(sc, VR_ISR, 0xFFFF);
status = CSR_READ_2(sc, VR_ISR);
CSR_WRITE_2(sc, VR_ISR, status);