RELEASED
PM73123 AAL1GATOR-8
DATASHEET
PMC-2000097
ISSUE 2
8 LINK CES/DBCES AAL1 SAR
10.4.1 R_OAM_QUEUE_TBL
Organization: 2 words
Base address within A1SP: 8000h
Index: 1h
Type: Read/Write
Function: OAM cells received from the ATM side are stored in a FIFO queue in
the memory. Head and tail pointers are used to keep track of the read and write
locations of the OAM cell buffers. There are 256 cell buffers in the OAM receive
queue. Of these 256 cell buffers, 255 are usable. The 256th buffer is used to
detect a full queue as follows:
When the queue is empty, OAM_HEAD = OAM_TAIL = N. When a cell is
received, the cell is written into the buffer at index (OAM_TAIL + 1) mod 256, and
OAM_TAIL is replaced with (OAM_TAIL + 1) mod 256. When the processor
receives an interrupt, it reads the cell at the buffer index (OAM_HEAD + 1) mod
256. After completing the read, it sets OAM_HEAD to (OAM_HEAD + 1) mod
256. This process is continued until OAM_HEAD = OAM_TAIL, at which time the
OAM receive queue is empty. The receive OAM interrupt can be cleared by
asserting the CLR_RX_OAM_LATCH bit in the CMD_REG.
If an OAM cell arrived between the time the OAM_TAIL was last read and
CLR_RX_OAM_LATCH was asserted, this OAM cell’s arrival can be detected
within the interrupt service routine by re-reading OAM_TAIL after
CLR_RX_OAM_LATCH was asserted.
OAM Queue Format
Offset
Name
OAM_HEAD
OAM_TAIL
Description
0
1
Head pointer
Tail pointer
OAM_HEAD Word Format
Field(Bits)
Description
OAM_HEAD
(7:0)
The microprocessor should increment to the next
cell location when it reads a cell. Initialize to 0.
PMC-SIERRA, INC. PROPRIETARY AND CONFIDENTIAL
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PMC [ PMC-SIERRA, INC ]
