static unsigned short get_reg (int regno)
{
    CS8900_PPTR = regno;
    return CS8900_PDATA;
}
 
static void put_reg (int regno, unsigned short val)
{
    CS8900_PPTR = regno;
    CS8900_PDATA = val;
}

    put_reg (PP_IA + 0, 0x00 | 0x09 << 8);
    put_reg (PP_IA + 2, 0x58 | 0xD8 << 8);
    put_reg (PP_IA + 4, 0x11 | 0x22 << 8);

    /* 只接收目標(biāo)地址為本網(wǎng)卡的無錯(cuò)誤數(shù)據(jù)包 */
    put_reg (PP_RxCTL, PP_RxCTL_IA | PP_RxCTL_Broadcast | PP_RxCTL_RxOK);
    /* 當(dāng)進(jìn)行接收操作時(shí)，不要產(chǎn)生任何中斷 */
    put_reg (PP_RxCFG, 0);
    /* 當(dāng)進(jìn)行發(fā)送操作時(shí)，不要產(chǎn)生任何中斷 */
    put_reg (PP_TxCFG, 0);
    /* 當(dāng)進(jìn)行緩存操作時(shí)，不要產(chǎn)生任何中斷 */
    put_reg (PP_BufCFG, 0);
    /* 使能發(fā)送和接收模式 */
    put_reg (PP_LineCTL, PP_LineCTL_Rx | PP_LineCTL_Tx);

/* initiate a transmit sequence */
    CS8900_TxCMD = PP_TxCmd_TxStart_Full;
    CS8900_TxLEN = length;

for (addr = packet; length > 0; length -= 2)
        {
            CS8900_RTDATA = *addr++;
        }

for (addr = (unsigned short *) &RxBuf[0], i = rxlen >> 1; i > 0;
         i--)
        *addr++ = CS8900_RTDATA;
    if (rxlen & 1)
        *addr++ = CS8900_RTDATA;

    struct mac_header *p = (struct mac_header*)(buf);
    memcpy (p->dest, NetServerEther, 6);
    memcpy (p->src, NetOurEther, 6);
    p->proto = htons(proto);

struct arp_header{
    unsigned short        ar_hrd;        /* Format of hardware address    */
    unsigned short        ar_pro;        /* Format of protocol address    */
    unsigned char        ar_hln;     /* Length of hardware address    */
    unsigned char        ar_pln;     /* Length of protocol address    */
    unsigned short        ar_op;        /* Operation            */

    unsigned char        ar_sha[6];    /* Sender hardware address    */
    unsigned long        ar_spa;     /* Sender protocol address    */
    unsigned char        ar_tha[6];    /* Target hardware address    */
    unsigned long        ar_tpa;     /* Target protocol address    */
}__attribute__ ((packed));


static int arp_handle( unsigned char *buf, unsigned int len )
{
    struct arp_header *pRx, *pTx;
    pRx = (struct arp_header *)(buf);
    pTx = (struct arp_header *)&TxBuf[256];

    switch (htons(pRx->ar_op))
    {
        case ARP_REQUEST:
            if (pRx->ar_tpa == htonl(NetOurIP))
            {
                pTx->ar_hrd = htons(0x01);
                pTx->ar_pro = htons(PROTO_IP);
                pTx->ar_hln = 0x06;
                pTx->ar_pln = 0x04;
                pTx->ar_op = htons(ARP_REPLY);
                memcpy(pTx->ar_sha, NetOurEther, 6);
                pTx->ar_spa = htonl(NetOurIP);
                memcpy (pTx->ar_tha, pRx->ar_sha, 6);      
                pTx->ar_tpa = pRx->ar_spa;
                mac_send( (unsigned char*)pTx, sizeof(struct arp_header), PROTO_ARP);
            }
            break;
        case ARP_REPLY:
            printf("\n\rGot ARP reply\n");
            break;
        default:
            printf("\n\r ar_op Not Support.\n");
            break;
    }
    return 0;
}

    struct ip_header *p = (struct ip_header*)(buf);
    p->ver_ihl = 0x45;                  // 1 Byte
    p->tos = 0x00;                      // 1 Byte
    p->tlen = htons(len);               // 2 Byte
    p->identification = htons(0x00);    // 2 Byte
    p->flags_fo = htons(0x4000);        // 2 Byte
    p->ttl = 0xFF;                      // 1 Byte
    p->proto = 17;                      // 1 Byte, 17 for UDP
    p->ip_src = htonl(NetOurIP);        // 4 Byte
    p->ip_dest = htonl(NetServerIP);    // 4 Byte
    p->crc = 0x0;                       // 2 Byte, To be
    p->crc = checksum( buf, sizeof(struct ip_header) );

unsigned short checksum(unsigned char *ptr, int len)
{
    unsigned long sum = 0;
    unsigned short *p = (unsigned short *)ptr;
    while (len > 1)
    {
        sum += *p++;
        len -= 2;
    }
    if(len == 1)
        sum += *(unsigned char *)p;
    while(sum>>16)
        sum = (sum&0xffff) + (sum>>16);
    return (unsigned short)((~sum)&0xffff);
}

    struct udp_header *P = (struct udp_header*)(buf);
    P->port_src = htons(0x8DA4); // 2 Byte
    P->port_dest = htons(port);  // 2 Byte
    P->tlen = htons(len);        // 2 Byte
    P->crc = 0x00;               // Do Not Checksum, 2 Byte


int tftp_download(unsigned char *addr, const char *filename)
{
    int i=0;
    unsigned short curblock = 1;

    tftp_send_request( &TxBuf[256], filename );
    msdelay(100);

    while (1)
    {
        eth_rx();
      
        if( pGtftp == NULL )
            continue;
        
        if ( ntohs(pGtftp->opcode) == TFTP_DATA )
        {
            if (ntohs(pGtftp->u.blocknum) == curblock)
            {
                printf("\r Current Block Number = %d", curblock);
                for (i=0; i<iGLen-4; i++)
                {
                    *(addr++) = *(pGtftp->data+i);
                }
                tftp_send_ack( &TxBuf[256], curblock);
                
                if (iGLen < TFTP_DATASIZE+4)
                {
                    break;
                }
                curblock += 1;
            }
            else if (ntohs(pGtftp->u.blocknum) < curblock)
            {
                tftp_send_ack( &TxBuf[256], ntohs(pGtftp->u.blocknum));
            }
            else
            {
                printf("\n\rBlock Number Not Match.");
                printf("Block Number = %d, curblock = %d\n", ntohs(pGtftp->u.blocknum), curblock);  
            }
        }
        else if ( ntohs(pGtftp->opcode) == TFTP_ERROR )
        {
            switch( ntohs(pGtftp->u.errcode) )
            {
               // 此處省略
            }
        }
        else if ( ntohs(pGtftp->opcode) == TFTP_RRQ )
        {}// 此處省略若干 else if
       
        pGtftp = NULL;
        iGLen = 0;
    }
    
    printf("\n\rTransfer complete: %d Bytes.\n\r", (curblock-1)*TFTP_DATASIZE + iGLen-4 );
    
    return 0;
}