RELEASED
PM73123 AAL1GATOR-8
DATASHEET
PMC-2000097
ISSUE 2
8 LINK CES/DBCES AAL1 SAR
the amount of weighting is programmable. The following formula is used to
determine the average buffer depth.
(PrevAvgDepth * (N-1)) + CurBufDepth
N
N = Weighting = 2^Adap_Filt_Size
PrevAvgDepth = Previous Average Buffer Depth
CurBufDepth = Current Buffer Depth
N must be a power of 2 and is controlled by the ADAP_FILT_SIZE field in the
A_ADAP_CFG register. If ADAP_FILT_SIZE equals ‘0’ then no filtering is done.
To enable quicker lock times, the window size will start small and will grow until it
matches the ADAP_FILT_SIZE parameter. The average value will reset when
either the line is disabled or it goes into underrun.
The value sent to the synthesizers is a truncated value of the Relative Buffer
Depth. Relative Buffer Depth is the difference between the calculated average
buffer depth and the CDVT setting (R_CDVT in the receive queue table) which
represents the ideal buffer depth value. The Relative Buffer Depth is limited to
represent a value of +/- 8 frames (ie, +/- 256 bytes) from the CDVT setting.
Relative buffer depths that exceed this value are truncated to a max/min value of
+/- 8 frames. Using a signed 8 bit data value, this corresponds to 1 bit
representing 2 bytes of data.
The frequency synthesizer will further cap this value by limiting the frequency
range to +/- 200 ppm for T1 and +/-100 ppm for E1.
Note that adaptive clocking, in general, is not well suited for voice applications
since low frequency or DC changes of the CDV will pass through most filters and
cause frame slips. Adaptive clocking is only supported for unstructured
connections inside the AAL1gator. If adaptive clocking is desired for structured
connections, it will need to be processed externally. The buffer depth will be
played out for each queue, but the information will be in frames. (the bottom 5
bits are invalid).
If an alternative algorithm is desired, this can be handled externally following an
architecture similar to what is shown in Figure 61. Note that the internal
synthesizers can be used via the CGC control port, so that only the adaptive
algorithm has to be in external logic and not the synthesizers.
PMC-SIERRA, INC. PROPRIETARY AND CONFIDENTIAL
146
PMC [ PMC-SIERRA, INC ]
