RELEASED
PM73123 AAL1GATOR-8
DATASHEET
PMC-2000097
ISSUE 2
8 LINK CES/DBCES AAL1 SAR
Figure 50 Overrun Detection
Write Pointer
R_MAX_BUF
1
Write Pointer
R_MAX_BUF
Read Pointer
2
Write Pointer
Read Pointer
(fixed)
R_MAX_BUF
3
Write Pointer
Read Pointer
4
Read Pointer
Write Pointer
R_MAX_BUF
R_CDVT
5
Read Pointer
U nderrun En d Pointer
(fixed)
Write Pointer
R_MAX_BUF
6
Old Location of Read Pointer
R_CDVT
Read Pointer = Underrun End Pointer
NOTES:
1. Normal operation.
2. If an overrun occurs, then the OVERRUN sticky bit is set and a forced underrun condition is set.
3. During the forced underrun condition, the write pointer is fixed, new data is dropped, and data in the buffer is played out, causing
the read pointer to increment. Each time a cell is received and dropped, the FORCED_UNDERRUN sticky bit is set.
4. The read pointer catches up to the write pointer, indicating a forced underrun condition, and the underrun condition is set.
Both pointersare advanced for each frame that the queue remains in the underrun condition. Conditioned underrun data is played
out.
5. When the first valid cell comes in, the RESUME sticky bit is set. The write pointer and the underrun end pointer are set to the
proper frame that is one R_CDVT ahead of the read pointer. Conditioned underrun data is played out.
6. Once the read pointer is equal to the underrun end pointer, then RESUME is complete and real data is now played out. Normal
operation now takes place.
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