a low-power cam design for lz data compression kun-jin lin and cheng-wen wu, ieee trans. on...

A Low-Power CAM A Low-Power CAM DesignDesign

for LZ Data for LZ Data CompressionCompression

Kun-Jin Lin and Cheng-Wen Wu, Kun-Jin Lin and Cheng-Wen Wu, IEEE Trans. On computersIEEE Trans. On computers, Vol. 49, No. 10, , Vol. 49, No. 10, Oct. 2000.Oct. 2000.

Presenter: Ming-Hsien TsaiPresenter: Ming-Hsien Tsai

OutlineOutline1.1. IntroductionIntroduction

2.2. CAM StructureCAM Structure

3.3. Removal of Redundant ComparisonsRemoval of Redundant Comparisons► Conditional Comparison MechanismConditional Comparison Mechanism► Redundancy AnalysisRedundancy Analysis

4.4. ConclusionConclusion

IntroductionIntroduction

1.1. CAMCAM ( (CContent ontent AAddressable ddressable MMemory) emory) has been considered the fastest has been considered the fastest architecture among all proposed architecture among all proposed hardware solutions for searching for a hardware solutions for searching for a given string , as required in LZ77.given string , as required in LZ77.

2.2. LZ77LZ77 is the lossless data compression is the lossless data compression algorithmalgorithm



3.3. Removal of Redundant ComparisonsRemoval of Redundant Comparisons► Conditional Comparison MechanismConditional Comparison Mechanism► Redundancy AnalysisRedundancy Analysis


CAM StructureCAM StructureTraditional SRAM Cell

Cross-coupled XOR GatePull-down Transistor Fig. 1. A typical CAM cell

CAM StructureCAM Structure

Fig. 1. A typical CAM cell

“1” “0”

“1”

“1”“0”

off on

offHigh-impedance

“0”

CAM StructureCAM Structure

Fig. 1. A typical CAM cell

“0” “1”

“1”

“1”“0”

off on

onlow

“1”



3.3. Removal Of Redundant ComparisonsRemoval Of Redundant Comparisons► Conditional Comparison MechanismConditional Comparison Mechanism► Redundancy AnalysisRedundancy Analysis


Conditional Comparison Conditional Comparison MechanismMechanism

Fig. 4. A typical match logic

The masking of unnecessary comparison results on the match nodes

Only match node is in the high-impedance when the word identical to input symbols


Fig. 4. A typical match logic

When all the words do not match

“1”“0”

“0”

“0”

“0”

If all words match

“1”

“0”

“0”


Fig. 5. Conditional comparison mechanism

Difference between CCM and typical match logic


Fig. 5. Conditional comparison mechanism

When all the words do not match

“1”“0”

“0”

“0”

“0”

If all words match

“1”

“0”“1

”

“1”“OFF

” “0”

The static current is totally blocked when “ mi ” is low

Redundancy AnalysisRedundancy Analysis

► Consider a typical data compressor using a Consider a typical data compressor using a CAM of CAM of 2,048 8-bit words2,048 8-bit words as the buffer as the buffer

► Assume that the input symbols are randomly Assume that the input symbols are randomly distributed. On average, only 2048 x1/256 = distributed. On average, only 2048 x1/256 =

8 words8 words can match any input symbol. can match any input symbol.

► There are 2048 – 8 = There are 2048 – 8 = 2,0402,040 words that will words that will require the power.require the power.

Redundancy AnalysisRedundancy Analysis

TABLE 1. Experimental Results on the Files from the Calgary Corpus

OutlineOutline

1.1. IntroductionIntroduction




ConclusionConclusion►We showed that the redundant We showed that the redundant

comparisons in the compression comparisons in the compression process can be removed process can be removed by turning off by turning off the power supply to those wordsthe power supply to those words that that do not need to participate, saving do not need to participate, saving about about 80 percent80 percent of the power of the power consumption of the comparison consumption of the comparison mechanism as compared with the mechanism as compared with the conventional CAM. conventional CAM.

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a low-power cam design for lz data compression kun-jin lin and cheng-wen wu, ieee trans. on...

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