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eh = *(mtod(m, struct ether_header *)); 2
eh.ether_type = ntohs((unsigned short)eh.ether_type); 3
m->m_data += sizeof(struct ether_header); 4
ADD_RECV_PACKET(ifp, sc, m->m_pkthdr.len); 5
if (eh.ether_dhost[0] & 0x1) {
ADD_RECV_MPACKET(ifp, sc, m->m_pkthdr.len);
}
i = READ_RXS(sc);
6
if (i &= 0x7ff) {
if ((i & 0x400) == 0) {
m_freem(m);
goto scrap;
}
}
ether_input(ifp, &eh, m);
7
}
}
1 Calls the io_blockread( ) routine to perform the data transfer from
the FIFO buffer on the adapter to the mbuf in host memory.
2 Makes a copy of the ether_header data structure for the
ether_input( ) routine.
3 Converts the 2-byte ether_type field from network byte order to host
byte order and saves it in the ether_header data structure.
4 Adjusts the pointer to the received data to point past the MAC header
(skips past the destination address, source address, and ether_type
fields).
5 Calls the ADD_RECV_PACKET macro to increment the receive packet
(block) count. If this packet was destined for a broadcast or multicast
address, calls the ADD_RECV_MPACKET macro to increment those
statistics as well.
6 Calls the READ_RXS macro to read the receive status. If the packet just
received was not fully received, scraps the packet.
7 Calls the ether_input( ) routine to process the received Ethernet
packet. The packet is in the mbuf chain without the ether_header
data structure, which is provided separately.
13.2.5 Discarding a Packet
The following code shows how the el_rint( ) routine discards a packet.
Some receive interrupt handlers perform a copy of a few bytes of the
packet to determine if the packet is actually destined for the device. Thus,
this task is an optional optimization.
scrap:
WRITE_CMD(sc, CMD_RXDTP);
1
status = READ_RXS(sc);
}
Implementing the Interrupt Section 13–9