
CN8236
5.0 Reassembly Coprocessor
ATM ServiceSAR Plus with xBR Traffic Management
5.4 Buffer Management
28236-DSH-001-A
Mindspeed Technologies
5-25
5.4.8.4 LANE-LECID
Packet Discard—Echo
Suppression on Multicast
Data Frames
The system designer can use this feature to discard superfluous traffic on the
ATM network caused by LAN Emulation Clients (LECs) transmitting multicast
frames, that is, point-to-multipoint Emulated LAN traffic.
If the LECID_EN bit in the RSM VCC table is a logic high, the
LANE-LECID discard function for that VCC is enabled, and the functions below
are performed:
The DPRI field is used as an index into the LECID table. This allows
support for up to 32 LECIDs, each a unique identifier for a single LAN
Emulation Client.
When the RSM coprocessor receives a BOM cell with this function
enabled, it checks the 16-bit LECID field in the LANE header against the
value in the LECID table. If a match occurs, the RSM coprocessor discards
the cell, marks the rest of the packet for discard, and increments the
SERV_DIS counter in the VCC table.
If the SERV_DIS counter rolls over, the CNT_ROVR bit in the next status
entry for this channel is set to a logic high. The CNT_ROVR bit in the
VCC table holds this flag information until a status is sent.
5.4.8.5 DMA FIFO Buffer
Full
The purpose of this function is to allow a graceful recovery from an incoming
DMA FIFO buffer full condition. Without this function, the reassembly
coprocessor is stalled when the FIFO buffer is full until recovery from the full
condition. This causes the cells to be dropped indiscriminately on the upstream
side of the reassembly block without any record of which VCCs the cells
belonged to. Upon recovery from the full condition, cells belonging to corrupted
PDUs continue to be processed, which wastes PCI bandwidth during the recovery
phase. This function provides for a more efficient use of host and SAR resources
by allowing the reassembly block to process and drop cells during the full
condition.
The reassembly block marks all channels that receive a cell during the full
condition for subsequent early packet discard. Upon recovery from the full
condition, the reassembly block performs early packet discard on the appropriate
channels as cells are received on those channels. In addition, cells continue to be
dropped on each channel until after an EOM cell is received for that channel.
Early packet discard processing is delayed until recovery from the full condition,
since the status entry also requires the use of the incoming DMA FIFO buffer.
This function is enabled by setting the FF_DSC bit in each VCC entry to a
logic high.
The user can want to disable this function if the free buffers, buffer
descriptors, and RSM status queues reside in SAR-shared memory.
Similarly, if RSM_CTRL1(OAM_QU_EN) is a logic high, RSM_CTRL1
(OAM_FF_DSC) should be set to a logic high.
The user can want to disable this function if the global OAM buffers, buffer
descriptors, and status queues reside in SAR-shared memory.
Early packet discard due to a FIFO buffer full condition is indicated by the
FFPD bit in the RSM status queue entry being a logic high.