參數(shù)資料
型號： MT90883
廠商： Zarlink Semiconductor Inc.
英文描述： TDM to Packet Processors
中文描述： TDM到分組處理器
文件頁數(shù)： 64/97頁
文件大?。?/td> 702K
代理商： MT90883
MT90880/1/2/3
Data Sheet
64
Zarlink Semiconductor Inc.
6.9.1 External Memory Requirements
The majority of the memory is used by the jitter buffer, which compensates for delay variation (PDV) in the
packet network. The amount of memory required to compensate for a given PDV depends on the mean size of
the packet payload. This is because for small packets, a large proportion of the packet is actually header. The
graph in Figure 27 shows the amount of packet delay variation that can be handled given the mean packet
payload size and the size of the external packet memory.
Figure 27 - PDV Supported for Different Memory and Packet Payload Sizes
6.9.2 Granule Structure
Memory on the MT9088x family is dynamically allocated in 128 byte blocks, known as "granules". Each granule
contains a 16-byte header section, used primarily for linking granules together into chains, and 112 bytes of
data. The granular organization of memory is responsible for the discontinuities in the graph shown in Figure
27, as the packet size grows to consume another granule.
The granule header contains information passed between the various internal blocks indicating how to handle
the information contained within the granule. Most importantly, it contains a pointer field indicating the location
of the next granule. This is used to chain granules together, initially to create large packets, and subsequently to
link packets together into queues.
To simplify flow of packets between functional blocks within the device, pointers are passed between blocks
indicating the location of the packet in memory. These pointers actually contain the location of the first granule
in a packet. Subsequent granules are indicated by the pointer field in the granule header.
Free granules are held centrally in a pool managed by a granule manager block. When granules are required
(e.g. during payload assembly or packet reception), the relevant block makes a request to the granule manager,
which returns a pointer to a free granule. Similarly, when a granule (or chain of granules) is no longer required
(e.g. the packet has been sent out of one of the output interfaces), it is released back to the free pool by
sending a granule release request to the granule manager.
6.9.3 Connecting the MT9088x to External Memory
The MT9088x is capable of interfacing to two types of external memory device, pipelined burst SRAM (such as
Micron
TM
's "Syncburst
TM
" family) and to the more bandwidth efficient types (such as Micron
TM
's "ZBT
" family),
which remove the turnaround cycles required when changing from a read to a write cycle. For most
applications, one external device is sufficient, as shown in the graph in Figure 27. All four memory capacities
shown in this graph can be implemented using one device (either 4, 8 or 16 Mbs). However, for more
0
50
100
150
200
250
1
32
64
96
128
256
512
1024
Packet Payload size, bytes
P
2 MByte memory
1 MByte memory
512 KByte memory
256 KByte memory
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
MT90883A 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:TDM to Packet Processors
MT90883A/IG 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:TDM to Packet Processors
MT90883BP1N 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:TDM to Packet Processors
MT90883IG 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:TDM to Packet Processors
MT9088IG 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:TDM to Packet Processors
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