AAL2 Implementation
MPC885 PowerQUICC Family Reference Manual, Rev. 2
44-20
Freescale Semiconductor
A description of the data flow shown in
Figure 44-9
is as follows:
•
The head of CPS-Packet (CID=1) has already been received (using the previous AAL0 buffer) and
has been stored in memory using the packet pointer in RPD 2. The tail of this packet (CID=1), now
in the first part of the active AAL0 buffer, is appended to the head, and RPD 2 is marked full (E=0).
•
Then, CPS-Packet (CID=19) is copied to memory using RPD 3, and RPD 3 is marked full (E=0).
•
Only the first part of CPS-Packet (CID=56) is in the active buffer, and it is stored in memory using
RPD 4.
•
Note that while the AAL2 processes the active AAL0 buffer (pointed to by AAL2_RACT_PTR),
the AAL0 may be filling another AAL0 buffer (pointed to by RBD_PTR) to be processed later.
44.6
Systems Restrictions When Using the AAL2 Functionality
Any combination of SCCs can run AAL2 channels; that is, all SCCs can activate AAL2. However, the
following restrictions apply:
•
Because AAL2 uses only one set of global AAL2 structures, each SCC should handle a unique set
of AAL2 channel numbers. No two SCCs should control the same AAL2 channel n.
•
AAL2 channel numbers can only be in the range 0–255.
NOTE
While the internal channels 0-31 can be used as AAL2 channels, care should
be taken that no conflict with possibly required raw cell queues in that range
occurs.
44.7
Global AAL2 Data Structures
The global AAL2 structures consist of the AAL2 parameter RAM, two programmable scratch areas for
internal use (AAL2_SCRATCH1 and AAL2_SCRATCH2), the CRC tables, the external CT pointer table
(AAL2_ECT_PTR_table), and the optional wait table (AAL2_TxWait_table). All the SCCs running
AAL2 share this one set of global AAL2 data structures. The following subsections discuss the AAL2
parameter RAM and the external CT pointer table.
44.7.1
AAL2 Parameter RAM
All global parameters and the pointers to global data structures are defined in the 64-byte AAL2 parameter
RAM area, starting at location (IMMR+0x3FC0—which is offset 0x1FC0 from the beginning of dual-port
RAM) in the parameter RAM. See
Figure 44-10
.
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