Motorola PowerQUICC II MPC8280 Series Reference Manual page 1230

IMA Microcode Architecture
The states are described as follows:
• Group Unassigned—This corresponds to a link which is known to be IMA, but for
which no information is known (e.g. IMA group number, IMA frame size). In this
state, the receive task only screens the incoming cells for ICP cells and discards all
others. ICP cells in which an SCCI change is noted are passed to a user-defined
receive channel, where software must interpret their content in order to initialize the
link and add it to the group. The link transitions to the 'Link IFSM Unsynchronized'
state when the link's 'Group Assigned' flag is set by software.
• Link IFSM Unsynchronized—In this state, the link state machine has not yet found
or validated the frame boundary for this link. This state is initially entered after
software defines the link's M value and expected ICP cell format, then sets the
'Group Assigned' flag. This state can be subsequently re-entered as the result of a
link defect. In this state, the link searches for an ICP cell, then looks for ICP cells in
the expected position of subsequent frames in order to validate frame
synchronization. Cells other than ICP cells are discarded. When the IFSM becomes
synchronized, an interrupt to the host is generated. The link transitions to the 'Link
Delay Unsynchronized' state when the link's group and link synchronization flags
are set appropriately by software.
• Link Delay Unsynchronized—This state contains two separate operations,
depending on the state of the group to which the link belongs. If the link enters this
state as the result of group start-up, it performs the "new-group link delay
synchronization algorithm". If the link enters this state while the group is already
activated (per the link addition/slow recovery (LASR) procedure of the IMA
standard), it performs the "added-link delay synchronization algorithm". As the
result of either algorithm, an interrupt will be generated to the host when delay
synchronization is achieved.
• No Link Defect—This is the state in which normal receive operation occurs after the
link has been established and the link-state has been communicated appropriately to
the far end. If the link is not inhibited at the group or link level, reception of ATM
cells will occur. If the link or group is inhibited, non-ICP received cells will be
replaced with filler cells. In the "no link defect" state, cells received (or their
replacements) are written to the link's delay compensation buffer. The link will
transition out of this state only as the result of an error or if reset by host software.
34.3.3.2 Cell Processing Activation Function
The cell processing activation function operates in two modes. The first, simplest mode is
for on-demand cell processing. The second mode is for cell processing as determined by
the reconstructed IMA data cell rate, as determined from the recovered receive data clock
of the timing reference link (TRL) of the IMA group.
34-20
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