2–184
Altera Corporation
Stratix II GX Device Handbook, Volume 2
October 2007
Native Modes
Figure 2–133
shows the input data codes versus the output data codes.
/D14.3/, /D24.0/, and /D15.8/ were replaced by /D5.6/ or /D16.2/ (for
/I1/, /I2/ ordered sets) and /D21.5/ (part of the /C2/ order set) was not
replaced.
Figure 2–133. Example of the Input Data Codes Versus the Output Data Codes
Rate Matching (Rate Matcher)
GIGE can operate in a multi crystal environment, so rate matching is
necessary to compensate for the frequency variations from different
crystals. Stratix II GX devices contain a built-in rate matcher
(12-word-deep FIFO buffer with control logic) that can tolerate up to, and
compensate for, a ±100 PPM frequency variation.
In the GIGE mode, rate matching occurs automatically in the rate
matcher. If the GMII protocol is followed, the /I/ sets (/I1/, /I2/) are sent
during the inter-frame gap (IFG). (The GMII protocol specifies 96-bits
long). The /I2/ ordered set (/K28.5/, /D16.2/) is added or deleted based
on how full or empty the rate matcher FIFO buffer is and if the current
running disparity is negative. The /I2/ order set contains two 10-bit code
groups. Two 10-bit groups (20-bits total) are deleted or added at a time. If
the number of words in the FIFO buffer (FIFO count) is greater than nine,
the FIFO buffer stops writing when the /I2/ ordered set is detected
(
Figure 2–134
). If the FIFO count is less than five, the FIFO buffer stops
reading and inserts the /I2/ ordered sets in place of the next FIFO data
(
Figure 2–135
).
1
The GIGE rate matcher does not have the capability of inserting
or deleting /C1/or /C2/ ordered sets.
If the rate matching FIFO buffer is in an underflow or overflow condition
(empty or full), the receiver outputs a /K28.4/ (
8'h9C + ctrl
). This
might happen if the PPM (parts per million) difference in the read and
write clock is too great, the IFG or IPG is too small (there are not enough
/I2/ code groups to remove), and/or the frame or packet size is too big.
K28.5
D14.3
K28.5
D24.0
K28.5
D15.8
K28.5
D21.5
tx_datain [ ]
clock
Dx.y
Dx.y
K28.5
D5.6
K28.5
D16.2
K28.5
D16.2
K28.5
tx_dataout
Ordered Set
D21.5
/I1/
/I2/
/I2/
/C2/
Содержание Stratix II GX
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