cn8236 Mindspeed Technologies, cn8236 Datasheet - Page 91

• Manufacturer Part Number: cn8236
• Description: Atm Servicesar Plus With Xbr Traffic Management
• Manufacturer: Mindspeed Technologies

CN8236
ATM ServiceSAR Plus with xBR Traffic Management
4.2.5 Status Reporting
4.2.6 Virtual FIFO Buffers
28236-DSH-001-B
The CN8236 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
CN8236 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 can contain the address of the buffer or of a host data
structure describing the buffer. To simplify host management, the CN8236 also
returns the VCC_INDEX of the VCC on which the buffer was transmitted.
In addition to gathering PDU data from buffers, the CN8236 provides an optional
method to segment from a fixed PCI address, or Virtual FIFO buffer. The
CN8236 supports AAL0, CBR Virtual FIFO buffer segmentation.
the CURR_PNTR and RUN fields to 0 in the SEG VCC table entry. The host
writes the FIFO buffer address to the FIFO_PNTR field in the VCC table entry.
The host also initially sets the SCH_MODE field = CBR.
buffer. Once the FIFO buffer is almost full, the host sets the RUN bit to a logic
high. The SAR then starts reading from the FIFO buffer. When the FIFO buffer
gets below almost empty, the host sets the SCH_OPT bit to a logic high. The SAR
then skips a cell transmit opportunity in order to allow the FIFO buffer to refill.
After the SAR skips a cell, it resets the SCH_OPT bit to a logic low.
host FIFO buffer, and prepends (that is, attaches to the beginning) the
ATM_HEADER value in the VCC table entry. The host does not use the transmit
queue for Virtual FIFO buffers. The CN8236 transmits cell payloads from this
location indefinitely, with no status reporting.
The CN8236 returns a user-supplied field (USER_PNTR) from the first SBD
The host configures the channel for Virtual FIFO buffer operation by setting
At this point the host can start writing cells to the external host transmit FIFO
In this mode, the segmentation coprocessor reads 48 bytes of payload from the
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Section
4.2 Segmentation Functional Description
3.2. The CN8236 reports status
4.0 Segmentation Coprocessor
Section
3.3.2.
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