LAN9313 Datasheet, PDF (64/398 Pages) SMSC Corporation – Three Port 10/100 Managed Ethernet Switch with MII

Three Port 10/100 Managed Ethernet Switch with MII
Datasheet
6.3.2 Transmit MAC
The transmit MAC generates an Ethernet MAC frame from TX FIFO data. This includes generating the
preamble and SFD, calculating and appending the frame checksum value, optionally padding
undersize packets to meet the minimum packet requirement size (64 bytes), and maintaining a
standard inter-frame gap time during transmit.
The transmit MAC can operate at 10/100Mbps, half- or full-duplex, and with or without flow control
depending on the state of the transmission. In half-duplex mode the transmit MAC meets CSMA/CD
IEEE 802.3 requirements. The transmit MAC will re-transmit if collisions occur during the first 64 bytes
(normal collisions), or will discard the packet if collisions occur after the first 64 bytes (late collisions).
The transmit MAC follows the standard truncated binary exponential back-off algorithm, collision and
jamming procedures.
The transmit MAC pre-pends the standard preamble and SFD to every packet from the FIFO. The
transmit MAC also follows as default, the standard Inter-Frame Gap (IFG). The default IFG is 96 bit
times and can be adjusted via the IFG Config field of the Port x MAC Transmit Configuration Register
(MAC_TX_CFG_x).
Packet padding and cyclic redundant code (FCS) calculation may be optionally performed by the
transmit MAC. The auto-padding process automatically adds enough zeros to packets shorter than 64
bytes. The auto-padding and FCS generation is controlled via the TX Pad Enable bit of the Port x MAC
Transmit Configuration Register (MAC_TX_CFG_x).
The transmit FIFO acts as a temporary buffer between the transmit MAC and the switch engine. The
FIFO logic manages the re-transmission for normal collision conditions or discards the frames for late
or excessive collisions.
When in full-duplex mode, the transmit MAC uses the flow-control algorithm specified in IEEE 802.3.
MAC pause frames are used primarily for flow control packets, which pass signalling information
between stations. MAC pause frames have a unique type of 8808h, and a pause op-code of 0001h.
The MAC pause frame contains the pause value in the data field. The flow control manager will auto-
adapt the procedure based on traffic volume and speed to avoid packet loss and unnecessary pause
periods.
When in half-duplex mode, the MAC uses a back pressure algorithm. The back pressure algorithm is
based on a forced collision and an aggressive back-off algorithm.
6.3.2.1
Transmit Counters
The transmit MAC gathers statistics on each packet and increments the related counter registers. The
following transmit counters are supported for each switch fabric port. Refer to Table 13.12, “Indirectly
Accessible Switch Control and Status Registers,” on page 253 and Section 13.3.2.25 through
Section 13.3.2.42 for detailed descriptions of these counters.
„ Total packets deferred (Section 13.3.2.25, on page 292)
„ Total pause packets (Section 13.3.2.26, on page 293)
„ Total OK packets (Section 13.3.2.27, on page 294)
„ Total packets 64 bytes in size (Section 13.3.2.28, on page 295)
„ Total packets 65 through 127 bytes in size (Section 13.3.2.29, on page 296)
„ Total packets 128 through 255 bytes in size (Section 13.3.2.30, on page 297)
„ Total packets 256 through 511 bytes in size (Section 13.3.2.31, on page 298)
„ Total packets 512 through 1023 bytes in size (Section 13.3.2.32, on page 299)
„ Total packets 1024 through maximum bytes in size (Section 13.3.2.33, on page 300)
„ Total undersized packets (Section 13.3.2.34, on page 301)
„ Total bytes transmitted from all packets (Section 13.3.2.35, on page 302)
„ Total broadcast packets (Section 13.3.2.36, on page 303)
Revision 1.2 (04-08-08)
64
DATASHEET
SMSC LAN9313/LAN9313i