M7020R datasheet(92/150 Pages) STMICROELECTRONICS

92 / 150 page

M7020R

92/150

272-bit SEARCH on Tables x272-configured Using Up to Eight M7020R Devices

The hardware diagram of the search subsystem of

eight devices is shown in Figure 66, page 94. The

following are the parameters programmed in the

eight devices.

– First seven devices (devices 0–6):

CFG = 10101010, TLSZ = 01, HLAT = 000,

LRAM = 0, and LDEV = 0.

– Eighth device (device 7):

CFG = 10101010, TLSZ = 01, HLAT = 000,

LRAM = 1, and LDEV = 1.

Note: All eight devices must be programmed with

the same value of TLSZ and HLAT. Only the last

device in the table must be programmed with

LRAM = 1 and LDEV = 1 (Device 7 in this case).

All other upstream devices must be programmed

with LRAM = 0 and LDEV = 0 (Devices 0 through

6 in this case).

Figure 68, page 96 shows the timing diagram for a

SEARCH command in the 272-bit-configured ta-

ble of eight devices for Device 0. Figure 69, page

97 shows the timing diagram for a SEARCH com-

mand in the 272-bit-configured table of eight de-

vices for Device 1. Figure 70, page 98 shows the

timing diagram for a SEARCH command in the

272-bit-configured table of eight devices for De-

vice 7 (the last device in this specific table). For

these timing diagrams three 272-bit searches are

performed sequentially. The following HIT/MISS

assumptions were made as shown in Table 43,

page 93.

The following is the sequence of operation for a

single 272-bit SEARCH command (also 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 used for

bits [271:136] of the data being searched in this

operation. DQ[67:0] must be driven with the 68-

bit data ([271:204]) to be compared against all

locations “0” in the four-word, 68-bit page. The

CMD[2] signal must be driven to logic '1.'

Note: CMD[2] = 1 signals that the search is a

272-bit search. CMD[8:3] in this cycle is ig-

nored.

– Cycle B: The host ASIC continues to drive the

CMDV high and applies SEARCH command

code ('10') on CMD[1:0]. The DQ[67:0] is driven

with the 68-bit data ([203:136]) to be compared

against all locations “1” in the four 68-bits-word

page.

– Cycle C: 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 used for

bits [135:0] of the data being searched.

CMD[8:7] signals must be driven with the bits

that will be driven on SADR[21:20] by this de-

vice if it has a hit. DQ[67:0] must be driven with

the 68-bit data ([135:68]) to be compared

against all locations “2” in the four 68-bits-word

page. The CMD[2] signal must be driven to logic

'0.'

– Cycle D: The host ASIC continues to drive the

CMDV high and applies SEARCH command

code ('10') on CMD[1:0]. CMD[8:6] signals must

be driven with the index of the SSR that will be

used for storing the address of the matching en-

try and the Hit Flag (see SEARCH-Successful

Registers (SSR[0:7]), page 23). The DQ[67:0] is

driven with the 68-bit data ([67:0]) to be com-

pared to all locations “3” in the four 68-bits-word

page. CMD[5:2] is ignored because the LEARN

Instruction is not supported for x272 tables.

Note: For 272-bit searches, the host ASIC must

supply four distinct 68-bit data words on

DQ[67:0] during Cycles A, B, C, and D. The

GMR Index in Cycle A selects a pair of GMRs in

each of the eight devices that apply to DQ data

in Cycles A and B. The GMR Index in Cycle C

selects a pair of GMRs in each of the eight de-

vices that apply to DQ data in Cycles C and D.

The logical 272-bit SEARCH operation is shown in

Figure 67, page 95. The entire table of 272-bit en-

tries is compared to a 272-bit word K that is pre-

sented on the DQ Bus in Cycles A, B, C, and D of

the command using the GMR and the local mask

bits. The GMR is the 272-bit word specified by the

two pairs of GMRs selected by the GMR Indexes

in the command’s Cycles A and C in each of the

eight devices. The 272-bit word K that is presented

on the DQ Bus in Cycles A, B, C, and D of the com-

mand is compared to each entry in the table start-

ing 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[23:0] lines (see SRAM ADDRESSING,

page 126).

Note: The matching address is always going to be

a location “0” in a four-entry page for 272-bit

SEARCH (two LSBs of the matching index will be

'00').

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