Flow ControlBCM5718 Programmer’s Guide
Broadcom®
January 29, 2016 • 5718-PG108-R Page 225
Statistics Block
The statistic block shown in Ta b le 8 6 is a common data structure. The relationships of flow control statistics are
discussed in this section. Xon/Xoff statistical counters are related to internal Ethernet controller flow control
states. Xon is associated to transmit enabled state and Xoff is associated to transmit disabled state. These Xon/
Xoff states are not part of the IEEE 802.3 specification; the Ethernet controller uses Xon/Xoff to manage flow
control state and transitions. The Xon/Xoff statistics provide programmers with a high level of granularity for the
measurement of Ethernet controller flow control performance in a LAN (see Appendix A: “Flow Control,” on
page 574).
Table 86: Statistic Block
Statistic Description
xoffStateEntered This counter is bumped under the following conditions:
• IEEE 802.3 MAC flow control pause frame received with valid CRC.
• (Pause_time > 0) The link partner requests transmission inhibit.
The counter increments independently of the enabled/disabled state of
Receive_MAC_Mode_Control.Flow_Enabled.
xonPauseFramesReceived This counter is incremented under the following conditions:
• IEEE 802.3 MAC flow control pause frame received with valid CRC.
• (Pause_time == 0) The link partner no longer requires the device family to
pause/wait/delay outgoing packets.
The counter increments independently of the enabled/disabled state of
Receive_MAC_Mode_Control.Flow_Enabled.
xoffPauseFramesReceived This counter is incremented under the following conditions:
• IEEE 802.3 MAC flow control pause frame received with valid CRC.
• (Pause_time > 0) The link partner requires the BCM5718 family to pause/
wait/delay outgoing packets.
The counter increments independently of the enabled/disabled state of
Receive_MAC_Mode_Control.Flow_Enabled.
outXon This counter is incremented under the following conditions:
• Transmit_MAC_Mode_Control.Flow_Enabled bit is set.
• (MAC_RX_MBUF_Low_Water_Mark > Threshold Value MAC resources are
available.
• (pause_time == 0) 802.3 MAC flow control frame is sent.
outXoff This counter is incremented under the following conditions:
• Transmit_MAC_Mode_Control.Flow_Enabled bit is set.
• (MAC_RX_MBUF_Low_Water_Mark < Threshold Value) MAC resources are
running low and a pause is desired.
• (pause_time > 0) IEEE 802.3 MAC flow control frame is sent.
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