MT92220BG Zarlink Semiconductor, MT92220BG Datasheet - Page 92

• Manufacturer Part Number: MT92220BG
• Description: Description = 1023 Channel Voice Over IP/AAL2 Processor ;; Package Type = Epbga ;; No. Of Pins = 608
• Manufacturer: Zarlink Semiconductor

MT92220
Data Sheet
The silence suppression information can also be fed to the process externally. When this is the case, a special PCM
code is used on the TDM bus. In this mode, 2 TSSTs must be used to feed the MT92220 with the transmit data.
When the last PCM byte of the packet is read off the H.110 bus is 00h and the associated time slot upper bit also
indicates 0, this means that the packet must be suppressed. Note that the TX unsigned PCM magnitude is
transmitted on the lower 7 bits of the associated time slot. If the code received is normal data (upper bit 1), then the
packet is valid. In this case, the external agent makes all the suppress/don't suppress decisions, but the MT92220
still calculates the CN or SID Energy and decides when to send and when not to send CN and SID packets.
The MT92220 also supports many modes in which it can send CN or SID packets. In the most common
configuration, it will suppress silence packets and send CN or SID packets at the beginning of silence periods, or
whenever it decides to update. It is also possible to configure it to suppress silence packets but never to send CN or
SID packets at any time. It also supports two modes in which it does not suppress packets. In the first one, it uses
the marker bit in RTP to indicate the beginning of a voice period; in the second, all silence packets are indicated
with a marker bit = ‘1’, as well as the first packet at the beginning of a voice period. Finally, instead of calculating its
own CN or SID energy and generating the packet itself, the MT92220 can use a preprogrammed CN or SID packet.
This preprogrammed packet can be of variable length, allowing spectral data to be passed along as well as an
energy value. Preprogrammed packets must be written into external SSRAM A by an agent through the CPU
interface and may be updated periodically. Because a pointer is given to the preprogrammed packet, its payload
may be changed in a glitch-free, atomic way. Spectral CN or SID packets may be up to 64 bytes in length.
The silence suppression process also monitors and counts underruns that occur on the RX TDM side. The
underrun information from the RX side is passed along and is written to the TX circular buffer. The silence
suppression process can thus keep a 16-bit Underrun Count of the number of underrun events that have occurred.
The format of the TX Silence Suppression Structure varies according to whether or not the silence suppression
decision is being taken internally or if it is being fed from an outside agent, and according to whether or not the
generated CN or SID packet will be a white energy value or a preprogrammed spectral value.
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Zarlink Semiconductor Inc.