ibm3206k0424 ETC-unknow, ibm3206k0424 Datasheet - Page 66

• Manufacturer Part Number: ibm3206k0424
• Description: Ibm Processor For Network Resources
• Manufacturer: ETC-unknow

IBM3206K0424
IBM Processor for Network Resources
Preliminary
General LCD Layout
Transmit Logical Channel Descriptor Data Structures
Logical Channel Data Structure on page 65 and Scheduling Portion of a Transmit Descriptor on page 67
show the layout of the transmit portion of a Logical Channel Descriptor. When initializing an LCD, any loca-
tions that are not written to a specific value should be initialized to zeros. Fields that typically need to be ini-
tialized to a non-zero value are flagged with a # in the structure below.
Note: This is only one possible layout of the transmit portion of the LCD. Some field locations vary and are
further defined later in this section.
Care must be taken when updating fields in the LCD and then immediately causing the updated fields to be
accessed by other IBM3206K0424 entities. For example, it is possible, although not likely, under the right
conditions, for a normal LCD update followed by a SEGBF cell enqueue operation to actually execute in
reverse order. This is due to IBM3206K0424 internal priority levels and could result in SEGBF fetching the
LCD data before it has been updated to the new value. For this reason, it is highly advisable to use the LCD
update mechanism in Cell/Packet Re-assembly (REASM).
The transmit portion of the LCD can be subdivided into three distinct parts based on which chip functions or
entities access that particular part of the LCD. The first three 64-bit words are scheduling related and are
accessed only by CSKED. The next two 64-bit words (four if using switch fabric header) are related to both
scheduling and segmentation and are accessed and shared by both CSKED and SEGBF. The words follow-
ing these shared locations are related only to segmentation and are accessed only by SEGBF. The number
of 64-bit words in this portion of the LCD can vary from one to three. The actual number being used in an LCD
is determined by the segmentation processor code entry point field of that LCD. The following figure is the
layout of the entire transmit portion of the LCD.
Overall Transmit LCD Layout
CSKED Scheduling Information
Three 64-Bit Words
CSKED/SEGBF Shared Information
Two 64-Bit Words
SEGBF Segmentation Information
Zero - Three 64-Bit Words
The three 64-bit words containing CSKED scheduling information can have four different formats depending
upon whether scheduling is based on virtual path parameters or is configured for ABR.
If LCD-based memory management is used, a 64-bit section is inserted at byte offset ‘18’X.
Packet Header
pnr25.chapt03.01
Page 66 of 676
August 14, 2000