MT90502_06 Datasheet, PDF (94/205 Pages) Zarlink Semiconductor Inc – Multi-Channel AAL2 SAR

MT90502
Data Sheet
Complex Silence Suppression TDM Channel Mapping
ct_c8
ct_frame
ct_d[0]
ct_d[1]
ct_d[2]
ct_d[3]
Local ADPCM Nibble
Local PCM Byte
Remote PCM Byte
ct_c8
ct_frame
ct_d[0]
ct_d[1]
Local PCM Byte
Remote PCM Byte
Figure 54 - Complex Silent Suppression Stream Configuration
Tx PCM
CODEC
Rx PCM
Tx PCM
Tx ADPCM
Rx ADPCM
Rx PCM
CT_D[0]
CT_D[3]
MT90502
CT_D[2]
CT_D[1]
UTOPIA
Figure 55 - ADPCM Complex Silent Suppression Stream Configuration
2.9.3.2 CPS-Packet Silence State
The procedure is identical for both remote and local channels, as the silence suppression function requires
information for both local and remote CPS-Packet mean values to consult the State Graph (see Figure 52) and
determine the CPS-Packet status. Therefore, a channel on which complex silence suppression is enabled must
have its transmit and receive direction streams mapped on consecutive stream and the same time slot (e.g., see
Figure 54, “Complex Silent Suppression Stream Configuration,” on page 94). For example, the transmission
stream_(odd) 17, time slot 4 the associated reception stream is reception stream_(even) 16 time slot 4.
Silence Suppression State Table
To determine a CPS-Packet status (i.e., voice, transitional & silence), the TX TDM will reference the local and
remote decibel energy levels in external memory. The table contains 2-bit values indicating a combination of local
and remote energy levels. Note the Silent State Graph as shown in Figure 52.
The Silence Suppression State Table (4KB) is located in the variable structures of TX SSRAM determined by the
‘Table Offset[20:12]’ field in the CPS-Packet Final Assembly Structure (see Figure 63). The MT90502 can
accommodate a different State Table for as many as 512 channels, as different channels may exhibit different line
characteristics. The Table Offset field in the CPS-Packet Final Assembly Structure (shown in Figure 63) points to
the base address of the Silence Suppression State Table for the associated channel.
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