Realtek network adaptor 8168E transmit/receive using loopback

Question

I am trying to transmit and receive from Realtek 8168E using loopback(For windows 7 platform) ( writing into tx buffer and reading from rx buffer) Reading rx buffer gives 0. On checking interrupt status register, TDU and RDU bit is set to 1 (Tx/Rx descriptor unavailable)

Network adaptor : Realtek 8168E

Data sheet referred : Realtek 8168B

Transmitter side configuration - Allocated a memory for TX descriptor as per the specification given in the data sheet (page no:55). Aligned descriptor to 256 byte alignment.

• Also allocated a separate buffer (TXBuffer) to store the data to be transmitted.

• Placed the address of TXBuffer into the specified field in the TX descriptor.

• Enabled the MAC loopback bit in the TX config register (40h).

• Then we have enabled the NPQ bit in the TxPoll register (38h).

• After that, we have done the NIC reset by offset 37h.

• Then we have enabled the loopback bit in BMCR register.

• Enabled the Tx OK, and Tx Descriptor Unavailable interrupts in interrupt mask register (3Ch).

• Placed the Tx Descriptor address into the MAC register TNPDS (20h).

• Then at last enabled the TE bit in command register (37h).

Similarly I did required configuration in Rx side.

Below are the buffer I have Given

    //TX Buffer desriptor
typedef struct _TMP_TBD_STRUC {
    ULONG       ulFrameLength;
    ULONG            VLAN_TAG;
       ULONG         TX_Buffer_Add_Low;
       ULONG         TX_Buffer_Add_High;
} TBD_TMP_STRUC, *PTBD_TMP_STRUC;

//RX Buffer desriptor
typedef struct _RMP_RBD_STRUC {
    ULONG       ulBufferSize;
    ULONG            VLAN_TAG;
       ULONG         RX_Buffer_Add_Low;
       ULONG         RX_Buffer_Add_High;
} RBD_RMP_STRUC, *PRBD_RMP_STRUC;

*PL. suggest with how to debug such situation. Also the correct seqeunce of Tx & Rx descriptor configuration, pl share. *