diff --git a/axdriver_net/src/fxmac.rs b/axdriver_net/src/fxmac.rs
index ff3e9bb..392deb5 100644
--- a/axdriver_net/src/fxmac.rs
+++ b/axdriver_net/src/fxmac.rs
@@ -1,18 +1,19 @@
+use crate::{EthernetAddress, NetBufPtr, NetDriverOps};
 use alloc::boxed::Box;
-use alloc::vec::Vec;
 use alloc::collections::VecDeque;
-use core::ptr::NonNull;
+use alloc::vec::Vec;
 use axdriver_base::{BaseDriverOps, DevError, DevResult, DeviceType};
-use crate::{EthernetAddress, NetBufPtr, NetDriverOps};
+use core::ptr::NonNull;
 
+use fxmac_rs::{self, xmac_init, FXmac, FXmacLwipPortTx, FXmacRecvHandler};
 use log::*;
-use fxmac_rs::{self, FXmac, xmac_init, FXmacLwipPortTx, FXmacRecvHandler};
 
 extern crate alloc;
 
 const QS: usize = 64;
 //const NET_BUF_LEN: usize = 1526;
 
+/// fxmac driver device
 pub struct FXmacNic {
     inner: &'static mut FXmac,
     rx_buffer_queue: VecDeque<NetBufPtr>,
@@ -22,6 +23,7 @@ unsafe impl Sync for FXmacNic {}
 unsafe impl Send for FXmacNic {}
 
 impl FXmacNic {
+    /// initialize fxmac driver
     pub fn init(mapped_regs: usize) -> DevResult<Self> {
         info!("FXmacNic init @ {:#x}", mapped_regs);
         let rx_buffer_queue = VecDeque::with_capacity(QS);
diff --git a/axdriver_net/src/lib.rs b/axdriver_net/src/lib.rs
index 0002780..8742b9c 100644
--- a/axdriver_net/src/lib.rs
+++ b/axdriver_net/src/lib.rs
@@ -1,13 +1,14 @@
 //! Common traits and types for network device (NIC) drivers.
 
 #![no_std]
+#![feature(const_mut_refs)]
 
-#[cfg(feature = "ixgbe")]
-/// ixgbe NIC device driver.
-pub mod ixgbe;
 #[cfg(feature = "fxmac")]
 /// fxmac driver for PhytiumPi
 pub mod fxmac;
+#[cfg(feature = "ixgbe")]
+/// ixgbe NIC device driver.
+pub mod ixgbe;
 mod net_buf;
 
 use core::ptr::NonNull;