Information

Enhanced Three-Speed Ethernet Controllers
MPC8308 PowerQUICC II Pro Processor Reference Manual, Rev. 1
16-134 Freescale Semiconductor
16.6.2.8 Flow Control
Because collisions cannot occur in full-duplex mode, gigabit Ethernet can operate at the maximum rate. If
the rate becomes too fast for a station’s receiver, the station’s transmitter can send flow-control frames to
reduce the rate. Flow-control instructions are transferred by special frames of minimum frame size. The
length/type fields of these frames have a special value.
Table 16-130 lists the flow-control frame structure.
If flow-control mode is enabled (MACCFG1[Rx_Flow] is set) and the receiver identifies a pause-flow
control frame, transmission stops for the time specified in the control frame. The controller completes any
frame in progress before stopping transmission and does not commence counting the pause time until
transmit is idle. During a pause, only a control frame can be sent (TCTRL[TFC_PAUSE] is set). Normal
transmission resumes after the pause timer stops counting, or resumes immediately if a pause frame with
a zero time-out is received. If another pause-control frame is received during the pause, the period changes
to the new value received.
16.6.2.9 Interrupt Handling
The following describes what usually occurs within an eTSEC interrupt handler:
• If an interrupt occurs, read IEVENT to determine interrupt sources. IEVENT bits to be handled in
this interrupt handler are normally cleared at this time. There are three kinds of interrupts:
— Receive data frame interrupts, when bits RXB or RXF in IEVENT are set
— Transmit data frame interrupts, when bits TXB or TXF in IEVENT are set
— Error, diagnostic, and special interrupts (all bits in IEVENT other than RXB, RXF, TXB, or
TXF)
Table 16-130. Flow Control Frame Structure
Size [Octets] Description Value Comment
7 Preamble — —
1 SFD — Start frame delimiter
6 Destination address 01-80-C2-00-00-01 Multicast address reserved for use in MAC frames
(or MAC station address)
6 Source address — —
2 Length/type 88-08 Control frame type
2 MAC opcode 00-01 Pause command
2 MAC parameter — Pause time as defined by the PTV[PT] field. The pause period is
measured in pause_quanta, a speed independent constant of 512
bit-times (unlike slot time). The most-significant octet is transmitted
first.
2 Extended MAC
parameter
— Pause time extended as defined by the PTV[PTE] field. The most
significant octet is transmitted first.
40 Reserved — —
4 FCS — Frame check sequence (CRC)