MPC8540 datasheet(746/1302 Pages) FREESCALE

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MPC8540 PowerQUICC III Integrated Host Processor Reference Manual, Rev. 1

14-120

Freescale Semiconductor

Three-Speed Ethernet Controllers

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. During

this pause, only a control frame can be sent (TCTRL[TFC_PAUSE] is set). Normal transmission

resumes after the pause timer stops counting. If another pause-control frame is received during the

pause, the period changes to the new value received.

14.6.2.8 Interrupt Handling

The following describes what usually occurs within a TSEC 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.

•

Process the TxBDs to reuse them if the IEVENT[TXB or TXF] were set. If the transmit

speed is fast or the interrupt delay is long, more than one transmit buffer may have been

sent by the TSEC; thus, it is important to check more than just one TxBD during the

interrupt handler. One common practice is to process all TxBDs in the interrupt handler

until one is found with R set. See Table 14-115.

•

Obtain data from the RxBD if IEVENT[RXC,RXB or RXF] is set. If the receive speed is

fast or the interrupt delay is long, the TSEC may have received more than one RxBD; thus,

it is important to check more than just one RxBD during interrupt handling. Typically, all

RxBDs in the interrupt handler are processed until one is found with E set. Because the

TSEC pre-fetches BDs, the BD table must be big enough so that there is always another

empty BD to pre-fetch. See Table 14-116.

Table 14-114. Flow Control Frame Structure

Size

[Octets]

Description

Value

Comment

Preamble

SFD

Start frame delimiter

Destination address

01-80C2-00-00-01 Multicast address reserved for use in MAC frames

Source address

Length/type

88-08

Control frame type

MAC opcode

00-01

Pause command

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 sent first.

Extended MAC

parameter

Extended pause control parameter as defined by the PTV[PTE]

field. The most-significant octet is sent first.

Reserved

—

FCS

Frame check sequence (CRC)

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