am79c850 Advanced Micro Devices, am79c850 Datasheet - Page 65

• Manufacturer Part Number: am79c850
• Description: Supernet-r 3
• Manufacturer: Advanced Micro Devices

causes the match and exact lines to be asserted. This
pattern will take much longer to apply than the minimal
set presented in table 2.
Destination address exact/inexact logic:
Since the destination address matching logic is identical
to the source address matching logic, the same test can
be applied as described in the previous section of this
document. These tests can be applied simultaneously
with the source address patterns.
PROGRAMMING METHODS
This section provides details of how the AF is intended
to be used. This section provides a description of the
methods to write entries into the AF, to find entries in the
AF and to invalidate entries in the AF.
Writing Entries into the AF
In order for the AF to perform the function of matching
addresses in network frames, the desired addresses
must be loaded into the CAM portion of the AF. The
following procedure should be followed to accomplish
this operation.
1. Write the comparand value into the NP comparand
2. Write the NP mask register if it is desired to mask any
3. Write the NP personality register with the desired
4. Write the “Write CAM” instruction into the NP
5. The status register should be read once the DONE
Note: The ERROR bit in the status register will not be
set if a “Write CAM” instruction is used when this bit is
set. The user has to read this bit status before attempt-
ing to write an entry into the CAM.
Finding Entries in the AF
Once a number of entries are resident in the AF, it may
be necessary to find one or more of them. The process
below should be used to perform this operation.
registers. Note that the comparand register will
retain any previous value if it is not overwritten.
portion of the comparand. Note that the mask
register will retain any previous value if it is not
overwritten.
configuration of the SA, SAX, DA and DAX bits. The
VALID bit must be set if this entry is to participate in
any comparisons (either NP or network). If the
VALID bit is not set, this entry may be overwritten
when another entry is written to the CAM. The SKIP
bit should be cleared if this it will be necessary to find
this entry through the NP interface at a later time.
Note that the personality register will retain any
previous value if it is not overwritten.
command register.
bit is set to ensure that the ERROR bit was not set.
P R E L I M I N A R Y
SUPERNET 3
1. Load the value of the comparand that it is desired to
2. Write the “Find” instruction into the NP command
3. Read the NP status register when the DONE bit is
Invalidating Entries in the AF
In conjunction with managing the contents of the AF, it
may be required to remove entries. This process is
called “invalidation.” To invalidate an entry in the AF, the
following steps should be followed.
1. Load the NP comparand register with the value of the
2. Write the “Find” instruction into the NP command
3. When the DONE bit is set, read the NP status
3a.If the FOUND bit is not set, there is no entry in the AF
3b.If the FOUND bit is set and the MULT bit is not set,
3c. If the FOUND and MULT bits are set, there is more
4. Write the “Clear all SKIP” instruction to the NP
find into the NP comparand register.
register. Note: the comparand is not modified by the
NP mask registers.
set. If the FOUND bit is set, there is at least one
matching entry in the AF that does not have its SKIP
bit set. If the MULT bit is also set, there is more than
one entry that matches the comparand that does not
have the SKIP bit set.
AF entry that is to be removed.
register.
register. Do one of the following:
that matches the comparand that does not have its
SKIP bit set.
there is only one entry in the AF that matches the
comparand that does not have its SKIP bit set. Write
the “Invalidate” instruction into the NP command
register.
than one entry in the AF that matches the comparand
that does not have its SKIP bit set. If all of these
entries should be invalidated, write the “Invalidate”
instruction followed by the “Find” instruction into the
NP command register repeatedly until the FOUND
bit is not set in the NP status register. If only one of
the multiple matching entries should be invalidated,
write the “Read CAM” instruction to the NP
command register, compare the contents read back
from the CAM to the desired comparand, mask and
personality. If the currently matching AF entry is the
one that should be invalidated, write the “Invalidate”
instruction to the NP command register. If the
currently matching AF entry should not be
invalidated, write the “Skip” instruction to the NP
command register and repeat the invalidate process
from the beginning.
command register.
AMD
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