MT92220BG Zarlink Semiconductor, MT92220BG Datasheet - Page 27

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

Data Sheet
Packets are managed in 7 queues. Each queue corresponds to a possible destination of a packet within the
module. In addition to the 4 queues containing packets for the 2 TX link outputs, there are also queues for packets
going to the Disassembly module, the RX CPU FIFO in external memory and the Packet Identifier module. Each of
these queues can be configured independently as to a maximum number of blocks it may contain This prevents a
single overflowing port to grab the entire SDRAM and rob properly functioning ports of the memory they need to
operate. The CPU agent can also seize blocks from the linked list to write its packets destined to the CPU. The
CPU must free those blocks once it has read them.
In addition to the block queues, there are also 7 handle queues, each handle queue being associated to the block
queues. The handle queues contain the handles identifying the packets contained within the block queue. These
handles detail all the characteristics of the packets and are passed between agents until they reach their final
destination. Each handle queue can be programmed to a 2
handle queues (especially after passing through the packet identification section), the blocks that contain the
packet itself are never moved.
Each time a packet handle is added to a handle queue, the number of blocks it occupies is added to the block fill of
the queue. Should the packet cause either the block fill or the handle fill to exceed their maximum values, the
packet will be discarded and a per-queue status bit will be set in registers, indicating the error that has occurred.
Note that the chip performs its own garbage collection, so no blocks in the linked list are ever left floating because
the packet to which they were associated was lost.
The network interface also supports multicast functionality: a single packet can be sent to multiple destinations
simultaneously. A notable exception is that if a packet is being sent to the packet identifier, it cannot be sent
anywhere else.
A module called the packet handler manages all of these queues using a small internal memory shown in the next
figure.
Payload
Forward Link
Handle
Multicast Sum
Field
Packet payload. 48 bytes per block.
Link to next block of packet. All zeros is invalid link (indicating
end of packet).
Used in TX. When packet is queued in multiple TX queues this is
decremented each time the packet is sent and the TX queue that
decrements it to 0 frees the cell memory.
Table 7 - Packet Block Format Table
Zarlink Semiconductor Inc.
n
Description
size. Note that while handles may be copied to a new
MT92220
27