Motorola PowerQUICC II MPC8280 Series Reference Manual page 1220

IMA Microcode Architecture
Cell n
7
6
1-5
Cell ID
Cell OAM
Label Link ID
Header
PTI/CLP = b1011
HEC = 0x64
Figure 34-4. IMA Frame and ICP Cell Formats
The IMA protocol must compensate for potential differences in delay between the different
links of the IMA group. The allowable delay differential for DS1/E1 links is 25ms, which
at E1 rates is equivalent to approximately 118 cells.
34.2.3.2 IMA Filler Cells
At the transmitting end, cells are transmitted continuously. If there are no ATM layer cells
to be sent between ICP cells within an IMA frame, then the IMA transmitter sends filler
cells to maintain a continuous stream of cells at the physical layer. The insertion of Filler
cells provides cell rate decoupling at the IMA sublayer. The Filler cells should be discarded
by the IMA receiver.
34.3 IMA Microcode Architecture
This chapter explains the architecture of the receive and transmit IMA microcode tasks.
34.3.1 IMA Function Partitioning
The IMA microcode performs only those functions with regular, critical real-time demands.
The other functions of IMA (e.g. control and management) are the responsibility of host
software. As such, the IMA microcode corresponds primarily to the user plane functions
defined in the IMA specification, and software must provide the layer management and
plane management functionality. The IMA microcode provides interrupts when interaction
with layer management and plane management is required.
34-10
Freescale Semiconductor, Inc.
IMA Frame
.....
ICP Cell
ICP Cell
9
8
11
10
IMA
ICP
Link
Stat. &
cell
FSN
SI Ctrl CI
offset
MPC8280 PowerQUICC II Family Reference Manual
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Cell 3 Cell 2 Cell 1
Cell 4
ICP Cell offset should be different for each link.
ICP cell offset is determined at start-up.
12 14 15
13 16
TX
IMA Grp.
TX TX
Stat. & timing test test
ID
ptrn.
info ctrl
Ctrl.
17 18-49 50 51
52-53
end to
RX
Link
X
test end CRC
info.
ptrn
ch.
Link information for links 0-31
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