8101 Datasheet, PDF (48/172 Pages) LSI Computer Systems – Gigabit Ethernet Controller

2.11.4 End Of Packet
The End of Packet Delimiter, referred to as EPD indicates the end of a
packet. The EPD consists of two codes, /T/ and /R/, inserted at the end
of the packet, as defined in IEEE 802.3z and shown in Table 2.8, and
also shown in Figure 2.3. To maintain synchronization on the proper word
boundaries, an outgoing packet must also have an even number of 10-bit
words transmitted. If the packet has an odd number of 10-bit words
transmitted after the /T/R/ codes, an extra /R/ code is inserted after the
/T/R/ (now a /T/R/R/) to meet the even word requirement, as defined in
IEEE 802.3z and shown in Figure 2.3.
The transmit 8B10B PCS section appends either the /T/R/ or /T/R/R/
codes to the end of each transmit packet.
The receive 8B10B PCS section constantly monitors the incoming 10B
bitstream. If the /T/R/ codes are detected, the end of packet indication is
given to the receive MAC, and the /T/R/ or /T/R/R/ codes are stripped
from the end of the packet. If the 8B10B PCS receiver detects the
transition from the nonidle pattern to an idle pattern (/I/ code stream)
without intervening /T/R/ codes, the packet is assumed to have a bad
EPD. Packets with a bad EPD are discarded if the controller is so
programmed. Refer to Section 2.13, “Packet Discard” for more details on
discards. Clearing the DIS_CWRD bit in “Register 8–Configuration 2‚"
Section 4.3.9, programs the controller to not discard packets with PCS
errors.
2.11.5 Idle
The interpacket gap time is filled with a continuous stream of codes
referred to as the idle pattern. The idle pattern consists of a continuous
stream of /I2/ codes, as defined in IEEE 802.3z and shown in Figure 2.3.
The running disparity during idle is defined to be negative. So, if the
running disparity after the last /R/ code of a packet is positive, a single
/I1/ code must be transmitted as the first idle code to make the running
disparity negative. All subsequent idle codes must be /I2/, as defined in
IEEE 802.3z and shown in Figure 2.3. The /I1/ and /I2/ codes are defined
in Table 2.8.
The transmit 8B10B PCS section inserts a continuous stream of
/I1/I2/I2/I2/…or /I2/I2/I2/I2/…codes between packets.
2-30
Functional Description
Copyright © 2000–2001 by LSI Logic Corporation. All rights reserved.