lan9303m Standard Microsystems Corp., lan9303m Datasheet - Page 89

• Manufacturer Part Number: lan9303m
• Description: Small Form Factor Three Port 10/100 Managed Ethernet Switch With Dual Mii/rmii/turbo Mii
• Manufacturer: Standard Microsystems Corp.

Small Form Factor Three Port 10/100 Managed Ethernet Switch with Dual MII/RMII/Turbo MII
Datasheet
SMSC LAN9303M/LAN9303Mi
6.4.11
6.5
6.5.1
6.5.1.1
6.5.2
Counters
A counter is maintained per port that contains the number of MAC address that were not learned or
were overwritten by a different address due to MAC Address Table space limitations. These counters
are accessible via the following registers:
A counter is maintained per port that contains the number of packets filtered at ingress. This count
includes packets filtered due to broadcast throttling, but does not include packets dropped due to
ingress rate limiting. These counters are accessible via the following registers:
The Buffer Manager (BM) provides control of the free buffer space, the multiple priority transmit
queues, transmission scheduling, and packet dropping. VLAN tag insertion and removal is also
performed by the Buffer Manager. The following sections detail the various features of the Buffer
Manager.
Packet Buffer Allocation
The packet buffer consists of 32KB of RAM that is dynamically allocated in 128 byte blocks as packets
are received. Up to 16 blocks may be used per packet, depending on the packet length. The blocks
are linked together as the packet is received. If a packet is filtered, dropped, or contains a receive
error, the buffers are reclaimed.
Buffer Limits and Flow Control Levels
The BM keeps track of the amount of buffers used per each ingress port. These counts are used to
generate flow control (half-duplex backpressure or full-duplex pause frames) and to limit the amount
of buffer space that can be used by any individual receiver (hard drop limit). The flow control and drop
limit thresholds are dynamic and adapt based on the current buffer usage. Based on the number of
active receiving ports, the drop level and flow control pause and resume thresholds adjust between
fixed settings and two user programmable levels via the
(BM_DROP_LVL),
Buffer Manager Flow Control Resume Level Register (BM_FC_RESUME_LVL)
The BM also keeps a count of the number of buffers that are queued for multiple ports (broadcast
queue). This count is compared against the
(BM_BCST_LVL), and if the configured drop level is reached or exceeded, subsequent packets are
dropped.
Random Early Discard (RED)
Based on the ingress flow monitoring detailed in
on page
if the
Yellow
randomly discarded based on the moving average number of buffers used by the ingress port.
Buffer Manager (BM)
Switch Engine Port 0 Learn Discard Count Register (SWE_LRN_DISCRD_CNT_0)
Switch Engine Port 1 Learn Discard Count Register (SWE_LRN_DISCRD_CNT_1)
Switch Engine Port 2 Learn Discard Count Register (SWE_LRN_DISCRD_CNT_2)
Switch Engine Port 0 Ingress Filtered Count Register (SWE_FILTERED_CNT_0)
Switch Engine Port 1 Ingress Filtered Count Register (SWE_FILTERED_CNT_1)
Switch Engine Port 2 Ingress Filtered Count Register (SWE_FILTERED_CNT_2)
Drop on Red
bit in the
82, packets are colored as Green, Yellow, or Red. Packets colored Red are always discarded
Buffer Manager Configuration Register (BM_CFG)
Buffer Manager Flow Control Pause Level Register
bit in the
Buffer Manager Configuration Register (BM_CFG)
DATASHEET
89
Buffer Manager Broadcast Buffer Level Register
Section 6.4.6, "Ingress Flow Metering and Coloring,"
Buffer Manager Drop Level Register
is set, packets colored Yellow are
(BM_FC_PAUSE_LVL), and
respectively.
is set. If the
Revision 1.3 (08-27-09)
Drop on