AN983B Datasheet, PDF (70/91 Pages) List of Unclassifed Manufacturers – PCI/miniPCI-to-Ethernet LAN Controller

AN983B PCI/miPCI Fast Ethernet Controller with integrated PHY
The PAUSE function operation is used to inhibit transmission of data frames for a specified period of
time. The AN983B supports full duplex protocol of IEEE802.3x. To support PAUSE function, the
AN983B implements the MAC Control Sub-layer functions to decode the MAC Control frames
received from MAC control clients and execute the relative requests accordingly. When the Full
Duplex mode and PAUSE function are selected after Auto-Negotiation completed, then the AN983B
enables the PAUSE function for flow control of full duplex application. In this section we will
describe how the AN983B implements the PAUSE function.
MAC Control Frame and PAUSE Frame
Fig - 14 MAC Control Frame Format
The MAC Control frame is distinguished from other MAC frames only by their Length/Type
field identifier. The MAC Control Opcode defined in MAC Control Frame format for PAUSE
function is 0001h. Besides, the PAUSE time is specified in the MAC Control Parameters
field with 2 Octets, unsigned integer, in the units of Slot-Times. The range of possible
PAUSE time is 0 to 65535 Slot-Times.
So, a valid PAUSE frame issued by a MAC control client (could be a switch or a bridge) will
contains:
1) The destination address is set equal to the globally assigned 48 bit mulitcast address
01-80-C2-00-00-01, or equal to the unicast address which the MAC control client wishes to
inhibit its transmission of data frames.
2) Filled the MAC Control Opcode field with 0001h.
3) 2 Octets of PAUSE time specified in the MAC Control parameter field to indicate the
length of time for which the destination is wished to inhibit data frame transmission.
Receive Operation for PAUSE function
Upon reception of a valid MAC Control frame, the AN983B will start a timer for the length of
time specified by the MAC Control Parameters field. When the timer value reaches zero
then the AN983B ends PAUSE state. However, a PAUSE frame should not affect the
transmission of a frame that has been submitted to the MAC (started Transmit out of the
MAC and can’t be interrupted). On the other hand, the AN983B shall not begin to transmit a
frame more than one Slot-Times after received a valid PAUSE frame with a non-zero
PAUSE time. If the AN983B receives a PAUSE frame with a zero PAUSE time value, then
Rev. 1.8
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