cn8237 Mindspeed Technologies, cn8237 Datasheet - Page 114

• Manufacturer Part Number: cn8237
• Description: Atm Oc-12 Servicesar Plus With Xbr Traffic Management
• Manufacturer: Mindspeed Technologies

5.0 Reassembly Coprocessor
5.2 Reassembly Functional Description
5-6
5.2.2.3 Operation
described in the
to a logic high.
VCI addresses to be processed, in order to reduce the memory size of the lookup
structures being accessed. VPIs are limited by VP_EN; and VCIs are limited by
VCI_RANGE in the VPI Index table entry, and BLK_EN in the VCI Index table
entry when EN_PROG_BLK_SZ is enabled.
Index table entries to blocks in the reassembly VCC table.
Virtual Circuits (SVCs), can be dynamically allocated with simple on-the-fly
index updates.
Upon reception of a cell, the reassembly coprocessor uses the VPI field as an
index into the VPI Index table, the base address of which is located at
RSM_TBASE(RSM_ITB) x 0x80. The maximum allowed VPI value for UNI
header operation is 255, and the maximum allowed VPI value for NNI operation
is 4095, controlled by the RSM_CTRL0(VPI_MASK) field. If the VPI_MASK
bit is a logic high (indicating UNI header operation), the four most significant bits
of the ATM header are ANDed with 0000. The RSM coprocessor uses the VPI
value to read the VPI Index table entry.
maximum allowed value of VCI[15:x] values for that VPI, and thus sets the
useable size of the VCI Index table for that VPI. If the value of VCI[15:x] of the
received VCI field in the ATM header is greater than the VCI_RANGE field in
the VPI Index table entry, or VP_EN is a logic low, the reassembly coprocessor
discards the cell and increments the CELL_DSC_CNT counter.
The CN8237 then reads the appropriate entry in the VCI Index table. The address
of the VCI Index table entry is derived as follows:
block of 64 reassembly VCC State table entries (or from one to 64 VCC State
table entries if EN_PROG_BLK_SZ is enabled), offset from the base address of
the reassembly VCC table. The VCC_INDEX value is derived by concatenating
the VCC_BLOCK_INDEX value with the VCI[x-1:0] bits from the received cell
header. Thus, VCI[x-1:0] from the received header points to the reassembly VCC
State table entry for that VCC.
VC_EN is a logic low, the cell is discarded and the CELL_DSC_CNT counter is
incremented. Optionally, the counter is not incremented if the AAL_TYPE field
has a value of 11. VC_EN allows idle cells to be filtered if the PHY layer has not
already done so.
counter.
The user can also enable the programmable block size for VCC table entries as
At system initialization, the user can also limit the valid range of both VPI and
VPI/VCI address pairs can now be preallocated in groups by mapping VCI
Once the reassembly process has been initiated, additional channels, Switched
The VCI_RANGE field in the VPI Index table entry is used to set the
The VCI_IT_PNTR indicates the base address of the VPI’s VCI Index table.
The VCC_BLOCK_INDEX in the VCI Index table entry selects a contiguous
The reassembly coprocessor reads the first word of the VCC table entry. If
If the channel is active, the CN8237 increments the CELL_RCVD_CNT
Mindspeed Technologies
VCI_IT_PNTR x 4 + VCI[15:x] x 4
VCC_INDEX = VCC_BLOCK_INDEX + VCI[x-1:0]
Section
ATM OC-12 ServiceSAR Plus with xBR Traffic Management
5.2.2.2, by setting EN_PROG_BLK_SZ(RSM_CTRL1)
™
28237-DSH-001-C
CN8237