DM9000驱动分析之发送

/*分析DM9000发生数据函数**/
/*
 *  Hardware start transmission.
 *  Send a packet to media from the upper layer.
 */
static int
dm9000_start_xmit(struct sk_buff *skb, struct net_device *dev)
{
	unsigned long flags;
	board_info_t *db = netdev_priv(dev);

	dm9000_dbg(db, 3, "%s:\n", __func__);

	if (db->tx_pkt_cnt > 1)
		return NETDEV_TX_BUSY;

	spin_lock_irqsave(&db->lock, flags);

	/* Move data to DM9000 TX RAM */
	//写数据到DM9000 Tx RAM中， 写地址自动增加
	writeb(DM9000_MWCMD, db->io_addr);

	/*将skb中的数据写入寄存器，然后发送字节改变*/
	(db->outblk)(db->io_data, skb->data, skb->len);
	dev->stats.tx_bytes += skb->len;

	db->tx_pkt_cnt++;
	/*第一个发送包立刻发送， 第二个排列到发送队列中去*/
	/* TX control: First packet immediately send, second packet queue */
	if (db->tx_pkt_cnt == 1) {
		dm9000_send_packet(dev, skb->ip_summed, skb->len);
	} else {
		/* Second packet */
		db->queue_pkt_len = skb->len;
		db->queue_ip_summed = skb->ip_summed;
		
		/*告诉网络协议栈，停止发送数据。*/
		netif_stop_queue(dev);
	}

	spin_unlock_irqrestore(&db->lock, flags);

	/* free this SKB */
	/*释放skb*/
	dev_kfree_skb(skb);
	
	return NETDEV_TX_OK;
}


/*当发送完成后，会触发一次发送完成的中断。 当然要去中断处理函数中*/
static irqreturn_t dm9000_interrupt(int irq, void *dev_id)
{
	struct net_device *dev = dev_id;
	board_info_t *db = netdev_priv(dev);
	int int_status;
	unsigned long flags;
	u8 reg_save;

	dm9000_dbg(db, 3, "entering %s\n", __func__);

	/* A real interrupt coming */

	/* holders of db->lock must always block IRQs */
	spin_lock_irqsave(&db->lock, flags); 

	/* Save previous register address */
	reg_save = readb(db->io_addr);		//存储以前的地址

	/* Disable all interrupts */   //屏蔽所有中断
	iow(db, DM9000_IMR, IMR_PAR);

	/* Got DM9000 interrupt status */
	int_status = ior(db, DM9000_ISR);	/* Got ISR */
	iow(db, DM9000_ISR, int_status);	/* Clear ISR status */

	if (netif_msg_intr(db))
		dev_dbg(db->dev, "interrupt status %02x\n", int_status);

	/* Received the coming packet */   //接受中断发生
	if (int_status & ISR_PRS)
		dm9000_rx(dev);

	/* Trnasmit Interrupt check */
	if (int_status & ISR_PTS)					//检测是否发送完成
		dm9000_tx_done(dev, db);

	if (db->type != TYPE_DM9000E) {
		if (int_status & ISR_LNKCHNG) {
			/* fire a link-change request */
			schedule_delayed_work(&db->phy_poll, 1);
		}
	}

	/* Re-enable interrupt mask */
	iow(db, DM9000_IMR, db->imr_all);		//使能中断

	/* Restore previous register address */
	writeb(reg_save, db->io_addr);		//恢复以前的地址

	spin_unlock_irqrestore(&db->lock, flags);

	return IRQ_HANDLED;
}


/*分析中断发送完成处理函数*/

static void dm9000_tx_done(struct net_device *dev, board_info_t *db)
{
	int tx_status = ior(db, DM9000_NSR);	/* Got TX status */	//得到发送的状态

	if (tx_status & (NSR_TX2END | NSR_TX1END)) {
		/* One packet sent complete */		//是一个包就发送完成
		db->tx_pkt_cnt--;
		dev->stats.tx_packets++;

		if (netif_msg_tx_done(db))
			dev_dbg(db->dev, "tx done, NSR %02x\n", tx_status);

		/* Queue packet check & send */		//如果超过2个，进入队列。发送
		if (db->tx_pkt_cnt > 0)
			dm9000_send_packet(dev, db->queue_ip_summed,
					   db->queue_pkt_len);
		netif_wake_queue(dev);   //唤醒发送队列
	}
}


/*
* 总结：
       1. 通知网络协议栈，停止发送队列
       2. 写skb数据到寄存器中去
       3. 释放skb资源
       4. 当发送完成后，唤醒发送队列
*/