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参数资料
型号： M7020R-083ZA1T
厂商： 意法半导体
英文描述： 32K x 68-bit Entry NETWORK SEARCH ENGINE
中文描述： 32K的× 68位进入网络搜索引擎
文件页数： 73/150页
文件大小： 996K
代理商： M7020R-083ZA1T
73/150
M7020R
The following is the sequence of operation for a
single 136-bit SEARCH command (see COM-
MAND CODES AND PARAMETERS, page 29).
–
Cycle A:
The host ASIC drives the CMDV high
and applies SEARCH command code ('10') on
CMD[1:0] signals. CMD[5:3] signals must be
driven with the index to the GMR pair for use in
this SEARCH operation. CMD[8:7] signals must
be driven with the bits that will be driven on
SADR[21:20] by this device if it has a hit.
DQ[67:0] must be driven with the 68-bit data
([135:68]) in order to be compared against all
even locations. The CMD[2] signal must be driv-
en to logic '0.'
–
Cycle B:
The host ASIC continues to drive the
CMDV high and to apply SEARCH command
code ('10') on CMD[1:0]. CMD[5:2] must be driv-
en by the index of the comparand register pair
for storing the 136-bit word presented on the DQ
Bus during Cycles A and B. CMD[8:6] signals
must be driven with the index of the SSR that
will be used for storing the address of the
matching entry and the Hit Flag (see SEARCH-
Successful Registers (SSR[0:7]), page 23). The
DQ[67:0] is driven with 68-bit data ([67:0]) to be
compared against all odd locations.
The logical 136-bit SEARCH operation is as
shown in Figure 51, page 76. The entire table of 31
devices (consisting of 136-bit entries) is compared
against a 136-bit word K that is presented on the
DQ Bus in Cycles A and B of the command using
the GMR and local mask bits. The GMR is the 136-
bit word specified by the even and odd global
mask pair selected by the GMR Index in the com-
mand’s Cycle A.
The 136-bit word K that is presented on the DQ
Bus in Cycles A and B of the command is also
stored in the even and odd comparand registers
specified by the Comparand Register Index in the
command’s Cycle B. In x136 configurations, the
even and odd comparand registers can subse-
quently be used by the LEARN command in only
the first non-full device.
Note:
The LEARN command is supported for only
one of the blocks consisting of up to eight devices
in a depth-cascaded table of more than one block.
The word K that is presented on the DQ Bus in Cy-
cles A and B of the command is compared with
each entry in the table starting at location “0.” The
first matching entry’s location address, “L,” is the
winning address that is driven as part of the SRAM
address on the SADR[21:0] lines (see SRAM AD-
DRESSING, page 126). The global winning device
will drive the bus in a specific cycle. On global miss
cycles the device with LRAM = 1 (the default driv-
ing device for the SRAM bus) and LDEV = 1 (the
default driving device for SSF and SSV signals)
will be the default driver for such missed cycles.
Note:
During 136-bit searches of 136-bit-config-
ured tables, the search hit will always be at an
even address.
The SEARCH command is a pipelined operation.
It executes a search at half the rate of the frequen-
cy of CLK2X for 136-bit searches in x136-config-
ured tables. The latency of SADR, CE_L, ALE_L,
WE_L, SSV, and SSF from the 136-bit SEARCH
command cycle (two CLK2X cycles) is shown in
Table 39, page 88.
The latency of a search from command to the
SRAM access cycle is 6 for 1–31 devices in the ta-
ble and where TLSZ = 10. In addition, SSV and
SSF shift further to the right for different values of
HLAT, as specified in Table 40, page 88.
The 136-bit SEARCH operation is pipelined and
executes as follows:
– Four cycles from the SEARCH command, each
of the devices knows the outcome internal to it
for that operation.
– In the fifth cycle after the SEARCH command,
the devices in a block (being less than or equal
to eight devices resolving the winner within
them using the LHI[6:0] and LHO[1:0] signalling
mechanism) arbitrate for a winner amongst
them.
– In the sixth cycle after the SEARCH command,
the blocks (of devices) resolve the winning block
through the BHI[2:0] and BHO[2:0] signalling
mechanism. The winning device in the winning
block is the global winning device for a
SEARCH operation.
Table 38. Hit/Miss Assumption
Search Number
1
2
3
4
Block 0
Miss
Miss
Miss
Miss
Block 1
Miss
Miss
Hit
Miss
Block 2
Miss
Hit
Hit
Miss
Block 3
Hit
Hit
Miss
Miss
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