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M7010R
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DEPTH-CASCADING
The Search Engine application can depth-cas-
cade the device to various table sizes in 68-bit,
136-bit, and 272-bit configurations by program-
ming the table size (TLSZ) field of the Command
Register. The devices perform all the necessary
arbitration to decide which device drives the
SRAM Bus. The latency of the searches increases
as the table size increases while the search rate
remains constant.
Depth-Cascading Up to Eight Devices (One
Block)
Figure 38, page 53 shows how up to eight devices
can cascade to form a 128K x68-bit, 64K x136-bit,
or 32K x272-bit table. It also shows the intercon-
nection between the devices for depth-cascading.
The host ASIC must program the table size (TLSZ)
field to '01.' Each Search Engine asserts the
LHO[1] and LHO[0] signals to inform downstream
devices in the cascade of its results. The LHI[6:0]
signals for any device are connected to the LHO
signals of the upstream device. A single device
alone drives the SRAM bus in any given cycle.
Depth-Cascading Up to 31 Devices (4 Blocks)
Figure 39, page 54 shows how to cascade up to
four blocks. Each block contains up to eight
M7010Rs (except the last block, which contains 7
devices), to form a 496K x68, 248K x136, or 124K
x272 table. Note the interconnection between
blocks for depth-cascading. The host ASIC must
program the table size (TLSZ) field to 10 for cas-
cading 8 to 31 devices (in up to four blocks). For
each search, a block asserts BHO[2], BHO[1], and
BHO[0].The BHO[2:0] signals for a block are only
taken from the last device in the block. See Figure
41, page 56 for the arbitration cycle between
blocks to determine which device drives the SRAM
Bus.
The device is configured to be the last in the
depth-cascaded table by setting LDEV to 1 in the
Command Register. The device with LDEV set to
1 drives the SSF and SSV signals in cycles when
all upstream devices do not drive these signals.
The M7010R with its LDEV Bit set drives SSF and
SSV during a search with a miss or with non-
search commands. See the LDEV Bit definition in
Table 10, page 20.
Depth-Cascading to Generate a “FULL” State
for a Block
Bit[0] of each of the 68-bit entries is designated as
a special bit (1 = FULL; 0 = Empty). For each
LEARN or PIO WRITE to the data array, each de-
vice asserts FULO[1] and FULO[0] if it does not
have any empty locations (see Figure 40, page
55). Each device combines the FULO signals from
the devices above it with its own full status to gen-
erate a FULL signal, which will then give a
“
full
”
status of the table up to the device asserting the
FULL signal. Figure 40, page 55 shows the hard-
ware connection diagram for generating the FULL
signal that goes back to the ASIC. In a depth-cas-
caded block of up to eight devices, the FULL sig-
nal from the last device should be fed back to the
ASIC controller to indicate the fullness of the table.
The FULL signal of the other devices should be left
open.
Note:
The LEARN Instruction is supported for up
to eight devices, whereas FULL cascading is al-
lowed for one block in tables containing more than
eight devices. In tables for which a LEARN Instruc-
tion will not be used, the Bit[0] of each 68-bit entry
should always be set to '1.'