cn8237 Mindspeed Technologies, cn8237 Datasheet - Page 75

• 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
3.3.1 Write-only Control Queues
28237-DSH-001-C
3.3.1.1 Control
3.3.1.2 Queue
Management
Variables
The host controls run-time segmentation and reassembly through write-only
control queues. There are two types of control queues—the segmentation transmit
queues and the reassembly free buffer queues. The host submits buffers of PDU
data for segmentation on the transmit queues, and supplies empty buffers for
received data on the free buffer queues. Each type of queue is managed as a
write-only control queue.
register pointers. To allow multiple clients, the CN8237 supports 32 queues of
each type. The SAR and host manage each queue independently, through queue
management variables. The SAR stores its variables in internal registers called
base tables. The host maintains its own variables within its driver. Each queue
contains a programmable number of queue entries.
Table 3-2
Table 3-2. Write-only Control Queue Variables
Figure 3-3
initializes all of the variables described in
maintains the READ pointer. When the SAR processes a queue entry, it advances
the READ pointer (READ++). Since the queues are circular, the pointer
eventually wraps back to 0. It also advances an internal counter, UPDATE
(UPDATE++). When INTERVAL queue entries have been processed, the SAR
writes its current position in the queue, READ, to a host variable, READ_UD.
The host determines the magnitude of INTERVAL at initialization. Larger
numbers result in fewer overhead PCI accesses, but also introduces larger latency
between host updates.
WRITE
READ_UD
READ
INTERVAL
UPDATE
READ_UD_PNTR
These queues reside in SAR-shared memory at locations defined by base
Variable
Mindspeed Technologies
describes the variables for write-only control queues.
illustrates the control queue management algorithm. The host
Current host position in
queue
Last known SAR position
in queue as seen by host
Current SAR position in
queue
Number of queue entries
processed by SAR before
writing READ_UD
Number of queue entries
since last write of
READ_UD
SAR pointer to READ_UD
Definition
™
Table
Host variable
Host word aligned
variable
SAR Base table
SAR register
SAR Base table
SAR Base table
3-2. Once the SAR is enabled, it
Location
3.3 Write-only Control and Status
3.0 Host Interface
Initialization
Host defined
&READ_UD
0
0
0
0
3-5