Motorola PowerQUICC II MPC8280 Series Reference Manual page 1189

packet belongs to an SSSAR CID, the receiver closes the SSSAR buffer with
RxBD[RxError = OS = 11] (oversized) and discards the rest of the frame.
The receiver issues an interrupt for each of the above errors.When a SSSAR buffer is closed
with RxBD[RxError = US or OS], indicating Uncompleted SDU or Oversized, then
RxBD[L] is set, and if RxQD[RFM]=1 then the receiver also issues an RXF interrupt.
Then, if no errors have occurred in the packet header, the packet CID is used to match the
PHY | VP | VC | CID with an RxQD; see Section 33.4.2, "Mapping of PHY | VP | VC |
CID." The match process yields an RxQD pointer. The RxQD indicates the type of SAR
operation to be performed on the PHY | VP | VC | CID. Three SAR operation modes are
supported:
• For the CPS sublayer, each packet from the CID is stored, as is, in a one packet
buffer.
• For switching, the packet is stored directly into the transmit buffer, and the CID is
translated.
• For the SSSAR sublayer, all packets received from the CID are reassembled into an
SSSAR SDU similar to the BD and buffer structures used for AAL5 frames.
• For the SSSAR sublayer, last packet UUI indication is stored in the last RxBD of the
SDU.
For the SSSAR sublayer, two additional parameters are verified for each new packet
received:
• RAS_Timer expiration. The RAS_Timer_Duration defined in the AAL2 parameter
RAM limits the time (starting when the first packet is received) allowed to receive a
complete SSSAR SDU. If this time limit is exceeded, the receiver closes the current
buffer with RxBD[RxError = TE = 01] (Ras_Timer expired) and starts a new
SSSAR frame with the next packet. When a buffer is closed with RxBD[RxError =
TE = 01], RxBD[L] is not set and the receiver does not issue an RXF interrupt.
• SSSAR_Max_SDU_Length. With each new packet the receiver checks whether the
current accumulated length of the SSSAR SDU exceeds the
SSSAR_Max_SDU_Length. If so, the receiver closes the current buffer with
RxBD[RxError = OS = 11] (oversized), discards the rest of the SSSAR SDU,
RxBD[L] is set, and if RxQD[RFM]=1 issues an RXF interrupt.
CIDs that have the same number but that are from different
AAL2 connections cannot use the same RxQD, unless they
never have split packets.
MOTOROLA
Freescale Semiconductor, Inc.
NOTE
Chapter 33. ATM AAL2
For More Information On This Product,
Go to: www.freescale.com
AAL2 Receiver
33-21