MPC8280 datasheet(1206/1386 Pages) FREESCALE

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Inverse Multiplexing for ATM (IMA)

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

34-60

Freescale Semiconductor

Figure 34-33. Near-End versus Far-End

34.5.4.3.2

As Responder (RX)

The IMA GSM/LSM software will receive ICP cells in the ICP buffer conveying the state of the FE’s

group and links. Once it has determined that the required minimum number of links are available, it can

proceed to enable the “group delay synchronization (GDS)” mechanism in which the all links in the

corresponding group are analyzed to find the one with the shortest propagation delay. The amount of delay

tolerated is programmable and is programmed via the setting of the beginning and ending addresses (size)

of the delay compensation buffers (DCB). Note that the size of all DCBs must be the same and must be

initialized before the GDS mechanism is activated. Activate GDS:

•

Set IGRSTATE[GDSS] to 1 (one) to enable GDS. Once GDS is enabled, the user must not alter

GDSS.

Once group delay synchronization is achieved, a “GDS” exception is generated. At this point, ATM stream

reconstruction can take place. In order for ATM stream reconstruction to be performed by the MPC8280,

the user must switch all links in the group to “active” mode (i.e., capable of receiving data cells), as

specified earlier in this section. The initialization of the ATM TX and RX data structures required to

generate and receive the ATM stream is out of the scope of this document, however, it is documented in

Chapter 31, “ATM Controller and AAL0, AAL1, and AAL5.”

34.5.4.4

Link Addition Procedure

Adding a link to an existing group requires changes to both the group and link table entries. Aside from

the normal exchange of ICP cells by the state machines at the FE and NE, the following steps should be

followed. In general, a new link entry is appended to the existing list of link table entries and the required

parameters initialized. This has no impact until the corresponding link is enabled via the PHYEN fields in

the IMA root table.

Tx ICP Template

ICP buffer

GSM/

LSM

GSM/

LSM

ICP buffer

Near-end

MPC8280

Far-end

MPC8280

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