CN8236EBGB Mindspeed Technologies, CN8236EBGB Datasheet - Page 114

• Manufacturer Part Number: CN8236EBGB
• Description: ATM SAR 155Mbps 3.3V ABR/CBR/GFR/UBR/VBR 388-Pin BGA
• Manufacturer: Mindspeed Technologies

Specifications of CN8236EBGB

• Package: 388BGA
• Traffic Class: ABR|CBR|GFR|UBR|VBR
• Utopia Type: Level 1|Level 2
• Host Interface: PCI
• Maximum Data Rate: 155 Mbps
• Typical Operating Supply Voltage: 3.3 V
• Minimum Operating Supply Voltage: 3 V

5.0 Reassembly Coprocessor
5.2 Reassembly Functional Description
5.2.2 Channel Lookup
Figure 5-3. Direct Index Method for VPI/VCI Channel Lookup
5-4
Block Size for VCC Table/
5.2.2.1 Programmable
Base Register (16)
RSM_TBASE
(RSM_ITB)
VPI [11:0]
VCI Index Table
VPI Index Table
VCI_IT_PNTR
The CN8236’s reassembly coprocessor implements a VPI/VCI index table
mechanism using direct index lookup in order to assign each cell to a virtual
channel, based on its VPI/VCI value. Each channel is thus identified by its
internally generated index value, the VCC_INDEX.
concatenated index values. It simplifies user channel assignment, provides
flexible provisioning for received traffic, and provides fast, consistent lookup
times regardless of the VPI/VCI values. In addition, using VPI/VCI table indexes
minimizes the memory impact in pre-allocating large numbers of channels by
requiring that only the VCI Index table entries be pre-allocated instead of the
VCC table entries.
Some users might have a requirement or desire to limit the amount of memory
allocated to VPI/VCI channel lookup. To enable this, the CN8236 provides the
user with the choice of enabling an alternative scheme for the memory allocation
and table handling involved in the Direct Index Lookup mechanism. In this
scheme, the user programs the size of the memory block of RSM VCC table
entries for all VCI Index table entries, to fit a range of 1 to 64 entries, instead of
the default 64 entries.
amount of memory space set aside for RSM VCCs, the total memory space
required for VCC allocation can be substantially lessened.
to a logic high. The SAR thus allocates block memory for VCC entries per VCI,
based on the value entered in VCI_IT_BLK_SZ (RSM_CTRL1).
This VPI/VCI table index mechanism dynamically maps VPI/VCIs to
Figure 5-3
Each RSM VCC entry requires 12 words of memory. By thus limiting the
To enable this scheme, set EN_PROG_BLK_SZ in the RSM_CTRL1 register
Mindspeed Technologies
VCI [15:6]
illustrates the direct index channel lookup mechanism.
(Max. 1024 entries
VCC_Block_Index
VCI Index Table
for each VPI)
ATM ServiceSAR Plus with xBR Traffic Management
(for one VPI)
™
(RSM_VCCB)
RSM_TBASE
VCI [5:0]
VCC Table Entries)
28236-DSH-001-B
(Block of 64
VCC Table
CN8236
8236_022