Altera Cyclone IV - Clock Frequency Compensation

Chapter 1: Cyclone IV Transceivers Architecture 1–63
Transceiver Functional Modes
February 2015 Altera Corporation Cyclone IV Device Handbook,
Volume 2
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, note that the rate match
FIFO is capable of inserting or deleting the first two bytes (/K28.5//D2.2/) of /C2/
ordered sets during auto-negotiation. However, the insertion or deletion of the first
two bytes of /C2/ ordered sets can cause the auto-negotiation link to fail. For more
information, refer to the Altera Knowledge Base Support Solution.
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
rx_rmfifodatadeleted
datain K28.5Dx.y
Dx.y
K28.5 D16.2 K28.5
First /I2/ Skip
Ordered Set
Second /I2/ Skip
Ordered Set
/I2/ Skip Symbol Deleted
Third /I2/ Skip
Ordered Set
D16.2 D16.2 Dx.y
dataout K28.5 Dx.yD16.2