EP4CE30F29C7N Datasheet, PDF (343/488 Pages) Altera Corporation – Cyclone IV Device Handbook, Volume 1

Chapter 1: Cyclone IV Transceivers Architecture
Transceiver Functional Modes
1–63
Clock Frequency Compensation
In GIGE mode, the rate match FIFO compensates up to ±100 ppm (200 ppm total)
difference between the upstream transmitter and the local receiver reference clock.
The GIGE protocol requires the transmitter to send idle ordered sets /I1/
(/K28.5/D5.6/) and /I2/ (/K28.5/D16.2/) during inter-packet gaps, adhering to the
rules listed in the IEEE 802.3 specification.
The rate match operation begins after the synchronization state machine in the word
aligner indicates synchronization has been acquired by driving the rx_syncstatus
signal high. The rate match FIFO deletes or inserts both symbols of the /I2/ ordered
sets (/K28.5/ and /D16.2/) to prevent the rate match FIFO from overflowing or
underflowing. It can insert or delete as many /I2/ ordered sets as necessary to
perform the rate match operation.
1 If you have the auto negotiation state machine in the FPGA fabric, the rate match
FIFO is also capable of deleting or inserting the first two bytes of the /C2/ ordered set
(/K28.5/D2.2/Dx.y/Dx.y/) to prevent the rate match FIFO from overflowing or
under running during the auto negotiation phase.
The status flags rx_rmfifodatadeleted and rx_rmfifodatainserted to indicate rate
match FIFO deletion and insertion events, respectively, are forwarded to the FPGA
fabric. These two flags are asserted for two clock cycles for each deleted and inserted
/I2/ ordered set.
Figure 1–58 shows an example of rate match FIFO deletion where three symbols must
be deleted. Because the rate match FIFO can only delete /I2/ ordered sets, it deletes
two /I2/ ordered sets (four symbols deleted).
Figure 1–58. Example of Rate Match FIFO Deletion in GIGE Mode
/I2/ Skip Symbol Deleted
First /I2/ Skip Second /I2/ Skip Third /I2/ Skip
Ordered Set
Ordered Set
Ordered Set
datain Dx.y K28.5 D16.2 K28.5 D16.2 K28.5 D16.2 Dx.y
dataout Dx.y K28.5 D16.2 Dx.y
rx_rmfifodatadeleted
October 2013 Altera Corporation
Cyclone IV Device Handbook,
Volume 2