VGE_ISR
status = CSR_READ_4(sc, VGE_ISR);
CSR_WRITE_4(sc, VGE_ISR, status);
status = CSR_READ_4(sc, VGE_ISR);
CSR_WRITE_4(sc, VGE_ISR, status);
CSR_WRITE_4(sc, VGE_ISR, 0xFFFFFFFF);
CSR_WRITE_4(sc, VGE_ISR, isr);