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IBM2520L8767
IBM Processor for ATM Resources
atmrm.chapt05.01
08/27/99
Receive AAL Processing (RAAL)
Page 275 of 553
Reassembly Timeout (RTO) Processing
Reassembly timeout processing is supported for AAL 5/6/7 LCs. It can be enabled on an LC basis by turning
on the RTO enable bit in the LC. The following registers also need to be properly set up to run RTO process-
ing:
RAALL LC Table Bound Registers
RAALL Reassembly Timeout value Register
RAALL Reassembly Timeout Pre-Scaler Register
See the register descriptions for more register details.
The LC table registers define the LC table that the RTO processor examines. The value register is used as a
compare value against a counter that counts based on a pre-scaler. Each time the registers compare, RTO
processing is started for a single LC and the time base is reset. RTO processing checks the RTO bit. If it is
reset, it sets it and continues. If it is set, then a timeout occurs and the LC is placed in error state and the
current packet is either freed or surfaced to the user via an event. The RTO bit is reset with each inbound cell
received or when a packet either completes or goes into error state.
Note:
If the RTO bit is set when RTO processing is disabled, it will remain set unless the LC goes into error
state. An LC needs to be touched twice to cause a timeout (once to set it and once to detect that it is already
set).
The time base starts running as soon as the RTO processing is complete. Currently, the RTO processing
takes the back seat if there are cells to be processed. So, RTO processing can be held off indefinitely.
Note:
For AAL0 FIFO RTO, it is assumed that the software will reset all counts and/or remove all cells from
the FIFO before resetting the state to idle. This needs to be done in order to maintain the reassembly count!
LC Statistics
If enabled, RAALL maintains LC level statistics. The following statistics are kept:
Total User Cells Received
Total User Cells Received with CLP=0
Using these numbers, the Total User Cells Received with CLP=1 can be calculated.
Both are 32-bit counters that wrap on overflow. Using the RAALL LC Statistics Overflow Register, the
overflow behavior of the counters can be changed to overflow on a value other than 0xffffffff. If enabled in the
mode reg, software is notified of overflow events via the counter overflow event queue specified in RXQUE.
Statistics can be enabled on a LC basis by turning on the statistics enable bit in the LC. Statistics can be
globally enabled/disabled across all LCs by setting the appropriate bit in the RAALL mode register. The global
enable/disable overrides all lc enables, and the global disable overrides the global enable.
If OAM blocking is enabled, then you might as well turn on statistics because you get them for free.