RS8234EBGC Mindspeed Technologies, RS8234EBGC Datasheet - Page 73

• Manufacturer Part Number: RS8234EBGC
• Description: RS8234EBGC ATM XBR SAR
• Manufacturer: Mindspeed Technologies

RS8234
ATM ServiceSAR Plus with xBR Traffic Management
Table 3-2. Write-Only Control Queue Variables
28234-DSH-001-B
WRITE
READ_UD
READ
INTERVAL
UPDATE
READ_UD_PNTR
Variable
3.3.1.1 Control
3.3.1.2 Queue
Management
Variables
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
Table 3-2
Figure 3-4
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 will
eventually wrap back to zero. 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 will also introduce larger
latency between host updates, which reduces the effective size of the queue.
Mindspeed Technologies
describes the variables for write-only control queues.
illustrates the control queue management algorithm. The host
Definition
Host variable
Host word aligned
variable
SAR Base Table
SAR register
SAR Base Table
SAR Base Table
™
Table
Location
3-2. Once the SAR is enabled, it
3.3 Write-Only Control and Status
3.0 Host Interface
Initialization
Host defined
&READ_UD
0
0
0
0
3-7