Freescale Semiconductor MPC8260 - Manual (Page 1167)

Inverse Multiplexing for ATM (IMA)
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor 33-65
Figure 33-33. Near-End versus Far-End
33.5.4.3.2 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
PowerQUICC II, 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 30, “ATM Controller and AAL0, AAL1, and AAL5.”
33.5.4.4 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.
33.5.4.4.1 Rx Steps
1. Reset all RX parameters in the new link table entry to zero.
Tx ICP Template
TX TX
Tx ICP Template
ICP buffer
GSM/
LSM
GSM/
LSM
ICP buffer
RX RX
Near-end
PowerQUICC II
Far-end
PowerQUICC II