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CHAPTER 5 SAR FUNCTION
169
(7)
When the
μ
PD98405 receives the first cell of the packet from the PHY layer device, it references the
lookup table to determine whether the cell is to be received or discarded.
(8)
When reception is enabled, the
μ
PD98405 accesses the VC table and assigns the batch of the pool to
that VC.
(9)
When the VC T1 timer function is enabled, the
μ
PD98405 also adds the VC to the T1 timer list and
monitors timeout.
(10) Each time the
μ
PD98405 receives a cell, it repeatedly transmits the cell to system memory in segment
units (when multi-cell transmission is disabled).
(11) If the batch becomes full before the completion of processing, the
μ
PD98405 fetches and assigns a
new batch.
(12) Once the last cell of the packet has been received,
(13) Whether an error has occurred is checked from the trailer information contained in the cell,
(14) Receive indication is issued to a specified mailbox, and the host is notified by an interrupt provided it is
not masked.
(15) The host reads the receive indication.
(16) Changes the read pointer of the mailbox.
(17) Receives the data from the pool.
(18) The host issues an Add_Batch command to add a batch if the remaining batches in the system
memory pool have been exhausted during reception.
The
μ
PD98405 also supports a raw cell reception function, used to receive traffic of other than AAL-5 type.
When this function is used, the received cells are transferred to system memory as is, in units of cells. During
raw cell reception, once a cell has been received (7)*, CRC-10 is checked (8)* then that cell is transferred to a
free buffer for the specified pool as raw cell data (9)*. Processing for raw cell reception is completed in units of
cells and no receive indication is stored to a mailbox, unlike AAL-5 packet reception. Each time a cell is stored,
the RCR bit of the GSR register is set, after which an interrupt is issued (10)*.
Remark
For a VC that uses the ABR service, received RM cells are not stored in system memory.
Instead, the
μ
PD98405 processes such cells internally.
The reception processing flow illustrated above merely outlines the reception processing.