8101 Datasheet, PDF (53/172 Pages) LSI Computer Systems – Gigabit Ethernet Controller

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.
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.
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.
Packet Discard
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