Table of Contents
Advertisement
Receive Operation
Types of Packets Received
The LANIC will only receive packets addressed to its station address (except
when promiscuous mode is configured). These packets may be individually
addressed, broadcast, or multicast, if the LANIC has been configured for such
operation. Packets that are shorter than minimum or longer than maximum are
not returned to the host, however, the statistical counters are updated.
Receive Buffer Managaement
The host is responsible for setting aside receive buffers in system memory. The
starting address and length of each buffer are sent to the LANIC via the RECV
command. These buffers are identified via a unique ID number. When the
LANIC fills a receive buffer, it returns the ID number to the host via the
Response Queue (RQ). From the time that the host enters the buffer descriptor
into the CQ until the LANIC returns the ID number in the RQ, the host must
ensure that the buffer is frozen in physical memory. Since neither the host nor
the LANIC have control over what time a packet arrives, there must be a
sufficient number of buffers ready for the LANIC to receive bursts of packets,
otherwise packets will be lost. For further information on lost packets, see the
paragraph "Receiver Blind Spots".
Queuing of Received Packets
Received packets may be queued by the LANIC before being reported to the
host. In order to report received packets to the host, the LANIC microprocessor
must access system memory. However, it may not be able to do this during a
burst of receive packets because the LANIC DMA capability will be saturated
with packet transfers to system memory. The microprocessor will update the RQ
as soon as a lull in received packet traffic occurs.
Receiver Blind Spots
Under certain conditions, the LANIC can fail to receive a packet. The following
conditions are necessary for the LANIC to receive a packet at any time:
The receiver must be turned on.
There must be a buffer ready to receive the packet.
The LANIC must be able to write to memory fast enough to prevent losing
data.
If any of the above conditions are not met, receive packets will be lost.
Principles of Operation
3-6
Advertisement
Table of Contents
