ethwrite.c

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/* ethwrite.c - ethwrite */

#include <xinu.h>

/*------------------------------------------------------------------------
 * ethwrite - enqueue a packet for transmission on TI AM335X Ethernet
 *------------------------------------------------------------------------
 */
int32   ethwrite (
        struct  dentry *devptr,
        void    *buf,
        uint32  count
    )
{
    struct  ethcblk *ethptr;    /* Ether entry pointer  */
    struct  eth_a_csreg *csrptr;    /* Ethernet CSR pointer */
    struct  eth_a_tx_desc *tdescptr;/* Tx Desc. pointer */
    struct  eth_a_tx_desc *prev;    /* Prev. Desc. pointer  */

    ethptr = &ethertab[devptr->dvminor];

    /* Get the pointer to the Ethernet CSR */
    csrptr = (struct eth_a_csreg *)ethptr->csr;

    /* Wait for an empty slot in the queue */
    wait(ethptr->osem);

    /* Get the pointer to the next descriptor */
    tdescptr = (struct eth_a_tx_desc *)ethptr->txRing +
                            ethptr->txTail;

    /* Adjust count if greater than max. possible packet size */
    if(count > PACKLEN) {
        count = PACKLEN;
    }

    /* Initialize the descriptor */
    tdescptr->next = NULL;
    tdescptr->buflen = count;
    tdescptr->bufoff = 0;
    tdescptr->packlen = count;
    tdescptr->stat = (ETH_AM335X_TDS_SOP |  /* Start of packet  */
              ETH_AM335X_TDS_EOP |  /* End of packet    */
              ETH_AM335X_TDS_OWN |  /* Own flag set for DMA */
              ETH_AM335X_TDS_DIR |  /* Directed packet  */
              ETH_AM335X_TDS_P1);   /* Output port is port1 */

    /* Copy the packet into the Tx buffer */
    memcpy((char *)tdescptr->buffer, buf, count);

    /* TODO Figure out why we need this hack    */
    /* This ethernet device does not send packets smaller than 60   */
    /* bytes; So pad a small packet to make it 60 bytes long    */

    if(count < 60) {
        memset((char *)tdescptr->buffer+count, 0, 60-count);
        tdescptr->buflen = 60;
        tdescptr->packlen = 60;
    }

    /* Insert the descriptor into Tx queue */

    if(csrptr->stateram->tx_hdp[0] == 0) {
        /* Tx queue is empty, this desc. will be the first */
        csrptr->stateram->tx_hdp[0] = (uint32)tdescptr;
    }
    else {
        /* Tx queue not empty, insert at end */
        prev = (struct eth_a_tx_desc *)
                csrptr->stateram->tx_hdp[0];
        while(prev->next != NULL) {
            prev = prev->next;
        }
        prev->next = tdescptr;
    }

    /* Increment the tail index of the Tx ring */
    ethptr->txTail++;
    if(ethptr->txTail >= ethptr->txRingSize) {
        ethptr->txTail = 0;
    }

    return count;
}