mt90502ag2 Zarlink Semiconductor, mt90502ag2 Datasheet - Page 95

• Manufacturer Part Number: mt90502ag2
• Description: Multi-channel Aal2 Sar
• Manufacturer: Zarlink Semiconductor

SID Transmission Operation
After the transmission of an SID, subsequent silent CPS-Packets are suppressed. However, the UUI sequence
count is maintained. Therefore the reception device can determine the number of CPS-Packets suppressed. Upon
the detection of silence the first suppressed CPS-Packet will be replaced by an SID packet and will contain the
Local Energy determined by the CPS-Packet Assembly Structure, without consideration of the Local Energy
Correction. Further SID CPS-Packets will be transmitted if the Local Energy is less than 3 dB of the last transmitted
SID energy level. Therefore, the energy level transmitted may gradually reduced over the silent period.
The ratio of silent packets to total CPS-Packets can be determined by consulting the CPS-Packet Final Assembly
Structure, SID Count and CPS-Packet Count fields (see Figure 62 and Figure 63).
SID Reception Operation
In the reception direction, SID CPS-Packets are employed to insert silent/comfort noise in Rx direction. The
MT90502 is required to compensate for suppressed CPS-Packets employing the CPS-Packet loss compensation
algorithm in the RX SAR (see Section 2.4.4, CPS-Packet Loss Compensation on page 60). Therefore, it is a
requirement to enable the CPS-Packet Loss Compensation employing the UUI sequence number counter in
silence suppression mode.
When the RX SAR receives an SID CPS-Packet and in the CPS-Packet Disassembly Structure (see Figure 24 on
page 54), LI0 field is configured for Silent Suppression the SID value will identify the Silent/Tone Buffer Number by
referencing the SID Byte to Silence Buffer Structure (see Figure 56 on page 95). The SID energy level is mapped
to the Silent/Tone Buffer Number in internal memory 1400h to 15FEh. For each SID byte, the Silence/Tone Buffer
Number is stored in the SID Byte to Silence Buffer memory location. Different silence buffers must be used
depending on the compression type. There are 5 entries for each SID byte, one per compression type:
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•
•
•
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The Silent/Tone Buffer Number is written to the ‘Tone Number to Insert’ field located in the RX TDM Control Memory
Structure (see Figure 31 on page 67) which identifies the ‘Silent/Tone Buffers’ (e.g., Figure 57 on page 96) in either
SSRAM, SDRAM or null byte insertion, for the associated channel. The contents of the ‘Silent/Tone Buffers’ is
inserted on the channel in place of the TDM Circular Buffer.
14C0h
1400h
1440h
1480h
1500h
Buffer no.: 0 - 63 for 64 tone buffers in SSRAM; 64 - 95 for 32 silent buffers in SDRAM; 96 - 127 for 32 null bytes in internal memory; 128
PCM 64 kb/s
ADPCM 40 kb/s
ADPCM 32 kb/s
ADPCM 24 kb/s
ADPCM 16 kb/s
SID Translation ADPCM (40 kbps)
SID Translation ADPCM (32 kbps)
SID Translation ADPCM (24 kbps)
SID Translation ADPCM (16 kbps)
SID Translation PCM (64 kbps)
for buffer number of previous SID packet.
Figure 56 - SID Byte to Silence Buffer Structure
Zarlink Semiconductor Inc.
MT90502
+3Ch
+2Eh
+3Eh
+00h
+30h
95
b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0
Buffer no. when SID byte is 30
Buffer no. when SID byte is 76 Buffer no. when SID byte is 77
Buffer no. when SID byte is 78
Buffer no. for all other SIDs
Reserved
Buffer no. when SID byte is 31
Buffer no. when SID byte is 79
Buffer no. when SID byte 127
Reserved
Data Sheet