Programmer’s Guide BCM5722
10/15/07
Broadcom Corporation
Document 5722-PG101-R Flow Control Page 172
Statistics Block
The statistic block shown in Table 88 is a common data structure. The relationships of flow control statistics are discussed
in this section. Xon/Xoff statistical counters are related to internal BCM5722 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 BCM5722 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 BCM5722 Ethernet
controller flow control performance in a LAN (see Appendix A ”Flow Control” on page 513).
Table 87: Keep_Pause Recommended Value
Register.Bit Recommended Value
Receive_MAC_Mode_Control.Keep_Pause DISABLED
Table 88: 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 BCM5722 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 BCM5722 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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