Table of Contents
Advertisement
Principles of Operation
QUEUE INITIALIZATION. Once operational, most of the communication between the host and the
LANIC is via a pair of queue structures in system memory. One queue, the Command Queue (CQ), is used
by the host to send commands to the LANIC. The other queue, the Response Queue (RQ), is used by the
LANIC to return status to the host. Each queue is fixed in size with fixed-length entries, however these
parameters are programmable when the queues are configured by the host. The head and tail pointers are
stored in system memory along with each queue. The host informs the LANIC of new entries in the CQ
by means of the READ_QUEUE command. The LANIC informs the host of new RQ
~ntries
by means of
the system interrupt facility.
Transmit Operation
TYPES OF PACKETS TRANSMITTED. The LANIC can transmit any size packet up to the maximum
packet size. Short packets are automatically padded to meet minimum packet length requirements.
TRANSMIT BUFFER MANAGEMENT.
The host is responsible for setting aside transmit buffers in
system memory. The starting address and length of each buffer is sent to the LANIC via the XMIT
request. Each buffer is identified by a unique ID number. When the LANIC has successfully transmitted
a transmit buffer, or when it encounters an irrecoverable error, it returns the ID number and status to the
host via the Response Queue (RQ). The host must ensure that transmit buffers are frozen in system
memory from the time the Xl\lIT request is entered into the CQ until the LANIC returns the buffer ID in
the RQ.
QUEUING OF TRANSMIT BUFFERS. The transmit operation requires a number of steps and there in
no way to predict when a transmit buffer is actually sent. Transmit buffers queue up in the CQ and in
an internal transmit queue. The buffer at the head of the transmit queue is processed when no receive
packets are being processed. Even then, there may be a delay due to the CSMA/CD protocol.
TRANSMIT OPERATION EXAMPLE. A transmit frame is assembled by the host in system memory.
The host then adds to the CQ an XMIT request containing the address and length of the transmit frame
and the ID number. The LANIC will process this command after it completes operations in progress and
gets the command from the CQ. The LANIC then copies the contents of the frame buffer from system
memory to its local memory. The next phase is undertaken by the 82586 LCC chip. The 82586 handles
the CSMA/CD protocol, serializes the data from the local memory buffer, sends it out on the network, and
generates the frame check sequence. After the 82586 LCC is finished with the frame, LANIC firmware
records the frame completion status and ID number in the RQ.
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.
Feb 85
3-4
Advertisement
Table of Contents
