enum {
    FWD_STOP_S1,
    FWD_STOP_S2,
    FWD_STOP_S3,
    FWD_STOP_S4,
    BKW_STOP_S1,
    BKW_STOP_S2,
    BKW_STOP_S3,
    BKW_STOP_S4,
    FWD_S1,
    FWD_S2,
    FWD_S3,
    FWD_S4,
    BKW_S1,
    BKW_S2,
    BKW_S3,
    BKW_S4
};