ATM Parameter RAM
MPC885 PowerQUICC Family Reference Manual, Rev. 2
38-12
Freescale Semiconductor
•
Address compression—See
Table 38-10
for the AM1–AM5 configuration for operation with
address compression.
•
Content-addressable memory (CAM)—See
Table 38-12
for the AM1–AM5 configuration for
CAM operation.
The address match parameter configuration when using the internal address look-up table
(SRSTATE[EXT] = 0) is shown in
Table 38-8
. See also
Section 39.1.1, “Internal Look-up Mechanism
(SRSTATE[EXT] = 0).”
HMASK is shown in
Figure 38-5
.
The HMASK fields are described in
Table 38-9
.
Table 38-8. AM1–AM5 Parameters for the Internal Look-up Table
Field
Name
Function
AM1
HMASK
Header mask. The ATM controller masks the header of each incoming cell with HMASK and uses
the resulting masked header in the address match process. The masking process uses a bitwise
AND function so bits are masked out by clearing the relevant bits in HMASK. The HMASK fields are
shown in
Figure 38-5
.
AM2
AM3
AMBASE Address matching table base. Used as a pointer to the address lookup table. It is scanned from the
top (AMEND) to the base, so headers for the busiest connections should be at the top of the table.
When a match occurs, the CP uses the location of the match to locate the channel number in the
pointer table.
Initialize AMBASE to point to the last entry of the lookup table. AMBASE must be word-aligned.
AM4
AMEND
Address matching end pointer. Contains the address of the top entry in the lookup table. New
connections are added to the table at the location immediately above AMEND. The match process
starts at the top (AMEND) and proceeds to the base (AMBASE).
AMEND is maintained by the user.
AM5
APBASE Address pointing table base. Contains the base address of a table of pointers to the connection
tables.
Initialize APBASE to point to the last pointer of the pointing table, which contains the offset of the
connection table for the global raw cell queue (channel 0). APBASE must be halfword-aligned.
0
3
4
11 12
27 28
30
31
GFC
VPI
VCI
PTI
CLP
Figure 38-5. HMASK
Table 38-9. HMASK Field Descriptions
Bit(s)
Name
Description
0–3
GFC
Generic flow control. Can be cleared to indicate that GFC protocol is not enforced.
4–11
VPI
Virtual path identifier mask
12–27
VCI
Virtual channel identifier mask
28–30
PTI
Payload type identifier mask
31
CLP
Cell loss priority mask
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