NEC Network Controller uPD98502 User Manual
Page 274
CHAPTER 4 ATM CELL PROCESSOR
274
Preliminary User’s Manual S15543EJ1V0UM
Figure 4-34. Receive Indication Format
UINFO
PACKET SIZE
31
16 15
0
TIME STAMP
31
0
PACKET START ADDRESS
31
0
1
VC Number
ERR CI C LP 0
ERR STATUS
0
POOL No.
31 30
16 15 14 13 12 11
8
7
5
4
0
UINFO
Pattern set by the host in the UINFO field in the VC table
PACKET SIZE
Size of the receive packet in cell units
TIME STAMP
Value of A_TSR when this indication is issued
PACKET START ADDRESS
Start address of the batch used
CHANNEL NUMBER
VC Number used by this VC
ERR
If 1, indicates that an error occurred while the packet was being received.
If 0, indicates that the packet was received normally.
CI
The PTI field in the header of at least one cell of the packet indicated congestion.
CLP
The CLP field in the header of at least one cell of the packet was equal to 1.
ERROR STATUS
Status of the error that occurred
0000
No error
0001
Free buffer underflow
0011
Max. number of bytes violation
0100
CRC-32 error
0110
Length error
0111
T1 time-out
POOL NUMBER
Number of the pool used
4.8.3.4 Receive errors
ATM Cell Processor checks errors while a packet is being received and also after the packet has been received.
Upon detecting an error, it reports the type of error, the start address and the amount of data that had been
transferred to system memory prior to the error being detected, using the receive indication in the mailbox.
Upon receiving a receive indication containing the error status, the V
R
4120A takes appropriate action and discards
the packet that caused the error. The types of reception errors are described below:
(1) Free buffer underflow
This error occurs if the free area in the free buffer is equal to or less than 48 bytes when a packet is received.
When this error occurs, an A_RQU interrupt is generated. If the discarded cell is an intermediate cell or the last cell of
the packet, reception of the packet is suspended. A receive indication reporting the free buffer underflow error is
issued, and the RID bit in the VC table is set. The remaining cells of the packet, including the last cell, are discarded,
and the RID bit is referenced. When the last cell is received, the RID bit is reset. If the cell discarded due to this error
is the first cell of the packet, an A_RQU interrupt is generated and the RID bit is set. No receive indication, however, is
issued.