Arria GX Architecture
GIGE Mode Rate Matcher
In GIGE mode, the rate matcher can compensate up to 100 PPM
(200 PPM total) frequency difference between the upstream transmitter
and the receiver. The rate matcher logic inserts or deletes /I2/ idle
ordered sets to/from the rate matcher FIFO during the inter-frame or
inter-packet gap (IFG or IPG). /I2/ is selected as the rate matching
ordered set since it maintains the running disparity, unlike /I1/ that
alters the running disparity. Since the /I2/ ordered-set contains two
10-bit code groups (/K28.5/, /D16.2/), 20 bits are inserted or deleted at a
time for rate matching.
1
The rate matcher logic has the capability to insert or delete /C1/
or /C2/ configuration ordered sets when ‘GIGE Enhanced’
mode is chosen as the sub-protocol in the MegaWizard Plug-In
Manager.
If the frequency PPM difference between the upstream transmitter and
the local receiver is high, or if the packet size is too large, the rate matcher
FIFO buffer can face an overflow or underflow situation.
Basic Mode
In Basic mode, you can program the skip and control pattern for rate
matching. There is no restriction on the deletion of a skip character in a
cluster. The rate matcher deletes the skip characters as long as they are
available. For insertion, the rate matcher inserts skip characters such that
the number of skip characters at the output of rate matcher does not
exceed five.
8B/10B Decoder
The 8B/10B decoder is used in all supported functional modes. The
8B/10B decoder takes in 10-bit data from the rate matcher and decodes it
into 8-bit data + 1-bit control identifier, thereby restoring the original
transmitted data at the receiver. The 8B/10B decoder indicates whether
the received 10-bit character is a data or control code through the
rx_ctrldetectport. If the received 10-bit code group is a control
character (Kx.y), the rx_ctrldetectsignal is driven high and if it is a
data character (Dx.y), the rx_ctrldetectsignal is driven low.
Altera Corporation
May 2008
2–23
Arria GX Device Handbook, Volume 1
ALTERA [ ALTERA CORPORATION ]
