Motorola PowerQUICC II MPC8280 Series Reference Manual page 1190

AAL2 Receiver
33.4.2 Mapping of PHY | VP | VC | CID
The AAL2 mapping mechanism translates a PHY | VP | VC | CID combination into an
RxQD. An RxQD can be unique per PHY | VP | VC | CID.
The mapping mechanism, shown in Figure 33-13, can be broken down as follows:
• Each ATM channel number (RCT) has its own CID mapping table. The mapping
table can be placed in internal or external memory (according to RCT[MAP]) and is
pointed to by RCT[CID Mapping Table Base]. The CID of the received packet is
used as an index into the mapping table.
• Each entry in the mapping table contains a 2-byte RxQD offset. This offset,
multiplied by 4, is the offset to an RxQD in either the internal or external RxQD
table.
• The two RxQD tables serve all the ATM channel numbers of an FCC.
(RxQD_Base_Int and RxQD_Base_Ext are defined in the FCC parameter RAM.)
• RxQD offsets from 8 through 511 point into the internal RxQD table located in
dual-port RAM at RxQD_Base_Int. Note that the first 32 bytes of the internal RxQD
table are reserved (so offsets 0–7 are reserved).
• RxQD offsets greater than 511 point into the external RxQD table located at
RxQD_Base_Ext + (512*4).
• Because the three types of RxQDs are different sizes, some offset numbers may not
be used.
33-22
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MPC8280 PowerQUICC II Family Reference Manual
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