DP83821 datasheet(30/86 Pages) NSC

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3.0 Functional Description (Continued)

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Table 3-9 Receive State Tables

FifoReady

(rxPktCnt > 0) or (rxPktBytes > rxDrainThreshold) ... in other words, if we have a complete

packet in the FIFO (regardless of size), or the number of bytes that we do have is greater than

the rxDrainThreshold, then we are ready to begin draining the rxDataFifo.

state

event

next state

actions

rxIdle

CR:RXEN && !CRDD

rxDescRead

start a burst transfer at address RXDP and a

length derived from RXCFG.

CR:RXEN && CRDD

rxDescRefr

start a burst transfer to refresh the link field of the

current descriptor.

rxDescRefr

XferDone

rxAdvance

rxDescRead

XferDone && !OWN

rxFIFOblock

XferDone && OWN

rxIdle

set ISR:RXIDLE.

rxFIFOblock

FifoReady

rxFragWrite

start a burst transfer from the RxDataFIFO to host

memory at fragPtr. The length will be the

minimum of rxPktBytes and descCnt. Decrement

descCnt accordingly.

(descCnt == 0) &&

(rxPktBytes > 0)

rxDescWrite

start a burst transfer to write the status back to

the descriptor, setting the OWN bit, and setting

the MORE bit. We'll continue the packet in the

next descriptor.

rxPktBytes == 0

rxDescWrite

start a transfer to write the cmdsts back to the

descriptor, setting the OWN bit and clearing the

MORE bit, and filling in the final receive status

(CRC, FAE, SIZE, etc.).

rxFragWrite

XferDone

rxFIFOblock

rxDescWrite

XferDone

rxAdvance

link != NULL

rxDescRead

RXDP <- rxDescCache.link. Clear CRDD. Start a

burst transfer at address RXDP with a length

derived from RXCFG:MAXF.

link == NULL

rxIdle

set CRDD. Set ISR:RXIDLE.

DP83821 Datasheet(PDF) 30 Page - National Semiconductor (TI)

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