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IXF1104 4-Port Gigabit Ethernet Media Access Controller
Datasheet 72
Document Number: 278757
Revision Number: 009
Revision Date: 27-Oct-2005
An IEEE 802.3 MAC PAUSE frame is identified by detecting all of the following:
• OpCode of 00-01
• Length/Type field of 88-08
• DA matching the unique multicast address (01-80-C2-00-00-01)
XOFF. A PAUSE frame informs the link partner to halt transmission for a specified length of time.
The PauseLength octets specify the duration of the no-transmit period. If this time is greater than
zero, the link partner must stop sending any further packets until this time has elapsed. This is
referred to as XOFF.
XON. The MAC continues to transmit PAUSE frames with the specified Pause Length as long as
the FIFO level exceeds the threshold. If the FIFO level falls below the threshold before the Pause
Length time expires, the MAC sends another PAUSE frame with the Pause Length time specified
as zero. This is referred to as XON and informs the link partner to resume normal transmission of
packets.
5.1.2.1.2 Pause Settings
The MAC must send PAUSE frames repeatedly to maintain the link partner in a Pause state. The
following two inter-related variables control this process:
• Pause Length is the amount of time, measured in multiples of 512 bit times, that the MAC
requests the link partner to halt transmission for.
• Pause Threshold is the amount of time, measured in multiples of 512 bit times, prior to the
expiration of the Pause Length that the MAC transmits another Pause frame to maintain the
link partner in the pause state.
The transmitted Pause Length in the IXF1104 MAC is set by the “FC TX Timer Value ($
Port_Index + 0x07)” on page 164.
The IXF1104 PAUSE frame transmission interval is set by the “Pause Threshold ($ Port_Index +
0x0E)” on page 166.
Figure 9. PAUSE Frame Format