urtw_rate2rtl
basic_rate = urtw_rate2rtl(48);
min_rr_rate = urtw_rate2rtl(12);
max_rr_rate = urtw_rate2rtl(48);
buf[2] |= (urtw_rate2rtl(2) << 3);
buf[3] = urtw_rate2rtl(MAX(2, urtw_get_rate(ic)));