RELEASED
PM73123 AAL1GATOR-8
DATASHEET
PMC-2000097
ISSUE 2
8 LINK CES/DBCES AAL1 SAR
value of this code ranges from –8 (1000) to +7 (0111). A higher value than had
been output previously indicates the remote clock is running faster than the local
clock. A lower value than had been output previously indicates the remote clock
is running slower than the local clock. The AAL1_CGC uses this value to
synthesize the TL_CLK. Since the frequency synthesizers accept 8 bit input
values, the lower 4 bits will be set to zero and the upper 4 bits will receive the
SRTS nibble. The synthesizers should be set for low resolution mode by
programming the HI_RES_SYNTH register bit in the LIN_STR_MODE memory
register to zero.
Figure 60 Receive Side SRTS Support
External to AAL1_CGC
R_SRTS_CDVT
Difference between
Remote SRTS and
Local SRTS
Cell Reception
SRTS Bit
Remote SRTS
SRTS
Queue
Extraction
Line Clock
Frequency
Latch
Divide by 3008
4-Bit Latch
Local SRTS
4-Bit Count
Input Reference Clock Frequency
NCLK (For T1/E1 = 2.43 MHz; For T3
= 77.76 MHz
4-Bit Counter
9.3.3.7 Adaptive
The Adaptive block determines the appropriate line clock frequencies based on
the buffer depth received from the A1SP. Every time a cell is received on a
particular line, the Adaptive block is given the current depth of the receive buffer.
If the buffer depth is increasing, then the local line clock is running slower than
the remote line clock. If the buffer depth is decreasing, then the local line clock
is running faster than the remote line clock. Therefore, the Adaptive block will
adjust the local line clock according to the buffer depth by passing the
appropriate value to the Frequency Synthesizer.
When CDV is accounted for, the buffer depth will not only vary due to differences
in the line clock frequencies, but also due to differences in the interarrival time of
cells. In order to truly measure the difference in the remote line clock frequency
and the local line clock frequency the buffer depth needs to be filtered. The
method the Adaptive block uses is a weighted moving average algorithm where
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145
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