XREG_RF_FREQ
rc = send_seq(priv, {0x00, XREG_RF_FREQ, 0x00, 0x00});
rc = send_seq(priv, {0x80, XREG_RF_FREQ, 0x00, 0x00});
return xc_write_reg(priv, XREG_RF_FREQ, freq_code);