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5-6
Mindspeed Technologies
28229-DSH-001-B
Transmission Convergence Block
CX28224/5/9 Data Sheet
5.2.3
Cell Screening
The CX2822x provides two optional types of cell screening. The first type, idle cell
rejection, prevents idle cells from being passed on. The second type, user traffic
screening, compares incoming bits to the values in the receive cell header registers.
Cells are rejected or accepted based on the bit patterns of their headers.
Idle cell rejection is enabled in bit 6 of the CVAL register (0x0C). If this bit is set to 1,
all incoming cells that match the contents of the Receive Idle Cell Header Control
Registers, RXIDL1–4 (0x20–23), are rejected. Individual bits in the Receive Idle Cell
Mask Control Registers, IDLMSK1–4 (0x24–27), can be set to 1 or Don’t Care,
causing the corresponding bits of the incoming cell to be treated as matching,
regardless of their value. If idle cell rejection is disabled, cells pass directly to user
traffic screening.
User traffic cell screening is similar to idle cell screening in that the incoming cells
are compared to the Receive Cell Header Control Registers, RXHDR1–4 (0x18–1B).
Individual bits in the Receive Cell Mask Control Registers, RXMSK1–4 (0x1C–1F),
can be set to 1 or Don’t Care, causing the corresponding bits of the incoming cell to be
treated as matching, regardless of their values. The RejHdr bit (bit 7) in the CVAL
register (0x0C) determines whether matching cells are rejected or accepted. If it is set
to 0, matching cells are accepted. If it is set to 1, matching cells are rejected. See
Table 5-2. Cell Screening—Matching
Receive Cell Mask Bit
Receive Cell Header Bit
Incoming Bit
Result
0
Match
00
1
Fail
01
0
Fail
0
1
Match
1
x
Match
Table 5-3. Cell Screening—Accept/Reject Cell
Cell
Reject Header
Result
Match
0
Accept Cell
Match
1
Reject Cell
Fail
0
Reject Cell
Fail
1
Accept Cell