CN8236EBGB Mindspeed Technologies, CN8236EBGB Datasheet - Page 206

• 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

6.0 Traffic Management
6.3 ABR Flow Control Manager
6-38
Turnaround RM Cells
Implicit ER Modification
6.3.7.6 Rate
Adjustment in
The system designer has various options for effecting a lowered explicit rate in
Turnaround RM cells.
Added to word 10 of the RSM VCC table entry and AAL3/4 head VCC entry are
the following: EN_IMP_CHG, CONG_ID. Added to word 9 is ERS_INDEX.
SCH_CNG(CONG_ID) is checked. If a logic high, the ER field is modified per
the mapping mechanism described below and written into TA_ER field of the
SEG VCC table entry. This mechanism provides an efficient per-connection
hardware reduction of ER values when turning around RM cells.
ER_HC_RATE table to provide programmable scaled reduction of the ER value
based on the value’s range. In addition, multiple ER_SHIFT tables and
ER_HC_RATE tables may be used to allow different VCCs to utilize different
mappings to ER_HC_RATE table entries. For example, different mappings may
be associated with various ABR templates. A 6-bit index, ERS_INDEX, located
the RS VCC table entry, indicates which ER_SHIFT table to use. The exponent
portion of the ER value is used as an index into the ER_SHIFT table. Thus, there
are 32 entries in each ER_SHIFT table. Each entry contains two values, the first,
HC_SHIFT, specifies the mantissa shift mask, and the second HC_INDEX,
specifies the address of an entry into the ER_HC_RATE table. For HC_SHIFT
values larger than 9, no ER_HC_RATE table lookup is performed, and the ER
value from the incoming RM cell is written into the TA_ER field in the SEG
VCC table. The number of rates in the ER_HC_RATE table for each exponent
value is determined by: 2^^(9 >> HC_SHIFT). The address of an ER_HC_RATE
table entry is calculated as (ER_SHIFT_B << 5 + HC_INDEX) + RM_CELL
mantissa [8:1] >> HC_SHIFT. The right entry for this address is chosen, if the bit
value of the RM_CELLS mantissa at its bit position HC_SHIFT is zero, and the
left otherwise. The new reduced rate is then
ER_SHIFT_B base address. Multiple ER_HC_RATE tables might be used.
When EN_IMP_CNG is a logic high and a forward RM cell is received,
The implicit ER reduction mechanism uses a ER_SHIFT table and the
The maximum index into the rate table has an offset of 4096 words to the
Mindspeed Technologies
2 ^^ HC_EXP (1
ATM ServiceSAR Plus with xBR Traffic Management
+
™
HC_MANT 512)
28236-DSH-001-B
CN8236