FreeBSD Device Drivers

Post Packet Transmission

Whenever an interface transmits a packet, it sends an interrupt. Naturally, this causes its interrupt handler to execute. Here is what executes in em(4):

static void
em_msix_tx(void *arg)
{
        struct tx_ring *txr = arg;
        struct adapter *adapter = txr->adapter;
        bool more;

        ++txr->tx_irq;

        EM_TX_LOCK(txr);
        more = em_txeof(txr);
        EM_TX_UNLOCK(txr);
        if (more)
              taskqueue_enqueue(txr->tq, &txr->tx_task);
        else
                E1000_WRITE_REG(&adapter->hw, E1000_IMS, txr->ims);
}

Note

Because of MSI, em(4) can use a different interrupt handler for post packet ...