ACXREG_INTR_ACK
CSR_WRITE_2(sc, ACXREG_INTR_ACK, intr_status);
CSR_WRITE_2(sc, ACXREG_INTR_ACK, ACXRV_INTR_FCS_THRESH);
CSR_WRITE_2(sc, ACXREG_INTR_ACK, ACXRV_INTR_CMD_FINI);