8101 datasheet(53/172 Pages) LSI

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Packet Discard

2-35

2.13.2 Receive Discards

Receive packets can be discarded if the error conditions listed in

Table 2.10 are detected. The discard behavior is dependent on whether

or not the packet is being output on the system interface when the

discard condition is detected. If the packet containing the error is not

being output on the system interface when the discard condition is

detected (an internal discard) the packet is discarded, (all data from the

packet containing the error is ﬂushed from the receive FIFO). If the

packet containing the error is being output on the system interface when

the discard condition is detected (an external discard) the RXDC pin is

asserted to indicate the error condition. Asserting the RXABORT pin or

setting the AUTORXAB bit in “Register 9–Conﬁguration 3‚"

Section 4.3.10, automatically discards the packet. For both internal and

external discarded packets, the appended status word is updated to

reﬂect the discard error condition.

Each of the receive discard conditions can be individually removed as a

discard condition by appropriately clearing the appropriate discard bit in

“Register 8–Conﬁguration 2‚" Section 4.3.9, associated with the

corresponding condition. When these bits are cleared, a packet that is

afﬂicted with the error condition indicated by that bit is not discarded.

Table 2.10

Receive Discard Conditions

Discard Condition

Description

Receive FIFO

overﬂow

Receive FIFO full. No more data accepted from

the 8B10B PCS.

CRC error

Receive packet has a CRC error.

Undersize packet

Receive packet is less than 64 bytes, exclusive of

preamble and SFD.

Oversize packet

Receive packet is greater than maximum packet

size, exclusive of preamble and SFD.

PCS codeword

error

Receive packet contains at least one word with an

8B10BPCS coding error.

RXABORT pin asserted RXABORT pin was asserted while the receive

packet was read out on the system interface. The

process of ﬂushing a receive packet with RXABORT

pin requires extra SCLK cycles equal to: (packet

length in bytes)/8 + 6.

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