EVB9311 SMSC, EVB9311 Datasheet - Page 78

• Manufacturer Part Number: EVB9311
• Description: EVALUATION BOARD LAN9311-NU
• Manufacturer: SMSC
• Series: 0133r

Specifications of EVB9311

• Main Purpose: Interface, Ethernet
• Embedded: No
• Utilized Ic / Part: LAN9311
• Primary Attributes: 2 Ports, 100BASE-TX/10BASE-T, Managed
• Secondary Attributes: 2 PHYs with HP Auto-MDIX, Auto- Flow Control, 32-bit CRC, MDI/MDI-X
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 638-1076

Revision 1.7 (06-29-10)
6.5.4
6.5.5
EGRESS RATE
SETTING
1589
3973
7947
158
396
794
0-3
12
19
39
78
4
5
6
7
9
Transmit Priority Queue Servicing
When a transmit queue is non-empty, it is serviced and the packet is read from the buffer RAM and
sent to the transmit MAC. If there are multiple queues that require servicing, one of two methods may
be used: fixed priority ordering, or weighted round-robin ordering. If the Fixed Priority Queue Servicing
bit in the
selected. Transmit queue 3 has the highest priority, followed by 2, 1, and 0. If the Fixed Priority Queue
Servicing bit in the
robin order is followed. Assuming all four queues are non-empty, the service is weighted with a 9:4:2:1
ratio (queue 3,2,1,0). The servicing is blended to avoid burstiness (e.g. queue 3, then queue 2, then
queue 3, etc.).
Egress Rate Limiting (Leaky Bucket)
For egress rate limiting, the leaky bucket algorithm is used on each output priority queue. For each
output port, the bandwidth that is used by each priority queue can be limited. If any egress queue
receives packets faster than the specified egress rate, packets will be accumulated in the packet
memory. After the memory is used, packet dropping or flow control will be triggered.
Note: Egress rate limiting occurs before the
The egress limiting is enabled per priority queue. After a packet is selected to be sent, its length is
recorded. The switch then waits a programmable amount of time, scaled by the packet length, before
servicing that queue once again. The amount of time per byte is programmed into the Buffer Manager
Egress Rate registers (refer to
definitions). The value programmed is in approximately 20 nS per byte increments. Typical values are
listed in
limiting the rate.
Note 6.3
priority queue will be serviced if a higher priority queue is being rate limited.
Table
TIME PER BYTE
Buffer Manager Configuration Register (BM_CFG)
These are the unlimited max bandwidths when IFG and preamble are taken into account.
158960 nS
15900 nS
31800 nS
79480 nS
1580 nS
3180 nS
7940 nS
6.5. When a port is transmitting at 10 Mbps, any setting above 39 has the effect of not
100 nS
120 nS
140 nS
160 nS
200 nS
260 nS
400 nS
800 nS
80 nS
Buffer Manager Configuration Register (BM_CFG)
Table 6.5 Typical Egress Rate Settings
76 Mbps
64 BYTE PACKET
BANDWIDTH @
Section 14.5.4.14
DATASHEET
870 Kbps
440 Kbps
220 Kbps
8.6 Mbps
4.4 Mbps
2.2 Mbps
66 Mbps
55 Mbps
48 Mbps
42 Mbps
34 Mbps
26 Mbps
17 Mbps
87 Kbps
44 Kbps
(Note
78
Two Port 10/100 Managed Ethernet Switch with 16-Bit Non-PCI CPU Interface
Transmit Priority Queue
6.3)
through
512 BYTE PACKET
96 Mbps
BANDWIDTH @
990 Kbps
490 Kbps
250 Kbps
2.5 Mbps
78 Mbps
65 Mbps
56 Mbps
49 Mbps
39 Mbps
30 Mbps
20 Mbps
10 Mbps
98 Kbps
49 Kbps
5 Mbps
Section 14.5.4.19
is set, a strict order, fixed priority is
(Note
6.3)
is cleared, a weighted round-
Servicing, such that a lower
1518 BYTE PACKET
SMSC LAN9311/LAN9311i
99 Mbps
BANDWIDTH @
for detailed register
500 Kbps
250 Kbps
100 Kbps
2.5 Mbps
80 Mbps
67 Mbps
57 Mbps
50 Mbps
40 Mbps
31 Mbps
20 Mbps
10 Mbps
50 Kbps
5 Mbps
1 Mbps
(Note
Datasheet
6.3)