cn8237 Mindspeed Technologies, cn8237 Datasheet - Page 89

• Manufacturer Part Number: cn8237
• Description: Atm Oc-12 Servicesar Plus With Xbr Traffic Management
• Manufacturer: Mindspeed Technologies

CN8237
ATM OC-12 ServiceSAR Plus with xBR Traffic Management
4.2.4 ATM PHY Layer Interface
4.2.5 Status Reporting
28237-DSH-001-C
4.2.3.2 AAL0
The CN8237 also supports a transparent or NULL adaptation layer, AAL0. AAL0
maps CPCS-SDUs directly to CPCS-PDU payloads. The SAR pads the SDU to a
48-byte cell payload boundary, but generates no other overhead. The SAR
generates the ATM header and PDU termination indications in the same manner
as it does with AAL5.
Once the segmentation coprocessor has formed an ATM cell, the CN8237
transfers the cell to the transmit FIFO buffer. The user chooses the length of this
FIFO buffer, with possible sizes from one to nine cells. The FIFO buffer depth is
programmable, since there is a trade-off between absorbing PCI latency with a
longer FIFO buffer, and introducing greater jitter.
trade-off in greater depth. Once sent to the transmit FIFO buffer, the cell passes
through the FIFO buffer to the PHY layer interface circuits.
The CN8237 informs the host of segmentation completion using segmentation
status queues. The host assigns each VCC to one of 32 status queues, enabling a
multiple peer architecture as described in
entry on either PDU or buffer boundaries, selectable on a per-VCC basis by
setting the STM_MODE bit. PDU boundary status is referred to as Message
Mode, while buffer status reporting is called Streaming Mode. Error conditions
also generate status queue entries, though this is a rare occurrence within a
CN8237 subsystem’s segmentation block. The segmentation status queues
operate according to the write-only host interface, defined in
associated with the status entry. The SAR does not use this field for any internal
purpose; it simply circulates the information back to the host. The value of
USER_PNTR must uniquely describe the segmented buffer associated with the
SBD. USER_PNTR may contain the address of the buffer or of a host data
structure describing the buffer. To simplify host management, the CN8237 also
returns the VCC_INDEX of the VCC on which the buffer was transmitted.
The CN8237 returns a user-supplied field (USER_PNTR) from the first SBD
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Section
4.2 Segmentation Functional Description
3.2. The CN8237 reports status
Section 6.2.3.3
4.0 Segmentation Coprocessor
Section
discusses this
3.3.2.
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