/* ethwrite.c - ethwrite */

#include 

/*------------------------------------------------------------------------
 * ethwrite - write a packet to an E1000E device
 *------------------------------------------------------------------------
 */
devcall ethwrite(
        struct  dentry  *devptr,        /* entry in device switch table */
        void    *buf,                   /* buffer that holds a packet   */
        int32   len                     /* length of buffer             */
        )
{
        struct  ethcblk *ethptr;        /* ptr to entry in ethertab     */
        struct  eth_tx_desc *descptr;/* ptr to ring descriptor  */
        char    *pktptr;                /* ptr used during packet copy  */
        uint32  tail;                   /* index of ring buffer for pkt */
        uint32  tdt;

        ethptr = ðertab[devptr->dvminor];

        /* Verify Ethernet interface is up and arguments are valid */

        if ((ETH_STATE_UP != ethptr->state)
                        || (len < ETH_HDR_LEN)
                        || (len > ETH_MAX_PKT_LEN) ) {
                return SYSERR;
        }

        /* If padding of short packet is enabled, the value in TX       */
        /*      descriptor length feild should be not less than 17      */
        /*      bytes */

        if (len < 17)
                return SYSERR;

        /* Wait for a free ring slot */

        wait(ethptr->osem);

        /* Find the tail of the ring to insert packet */
        
        tail = ethptr->txTail;
        descptr = (struct eth_tx_desc *)ethptr->txRing + tail;

        /* Copy packet to transmit ring buffer */
        
        pktptr = (char *)((uint32)descptr->buffer_addr & ADDR_BIT_MASK);
        memcpy(pktptr, buf, len);

        /* Insert transmitting command and length */
        
        descptr->lower.data &= E1000_TXD_CMD_DEXT; 
        descptr->lower.data = E1000_TXD_CMD_IDE |
                              E1000_TXD_CMD_RS | 
                              E1000_TXD_CMD_IFCS |
                              E1000_TXD_CMD_EOP |
                              len;
        descptr->upper.data = 0;

        /* Add descriptor by advancing the tail pointer */
        
        tdt = eth_io_readl(ethptr->iobase, E1000_TDT(0));
        tdt = (tdt + 1) % ethptr->txRingSize;
        eth_io_writel(ethptr->iobase, E1000_TDT(0), tdt);

        /* Advance the ring tail pointing to the next available ring    */
        /*      descriptor                                              */
        
        ethptr->txTail = (ethptr->txTail + 1) % ethptr->txRingSize;

        return len;
}