10GBASE-R Test PatternsIEEE 802.3ae 3/12/2001 10GBASE-R Test Patterns IBM Test Pattern • Want to...

10GBASE-R Test Patterns

John [email protected]

IEEE 802.3ae 3/12/2001

10GBASE-R Test Patterns IBM

Test Pattern• Want to evaluate “pathological” events that occur on

average once per day• At 10Gb/s “once per day” is equivalent to a

probability of 1.1×10–15 ~ 1/250

– Equivalent to 7.9σ for a Gaussian distribution• 231 – 1 PRBS repeats ~ 200ms

– Sufficient to meet worst case criteria of once per day?• 258 – 1 PRBS repeats in ~ 1 year

– Too long for practical testing

IEEE 802.3ae 3/12/2001


PCS

Test Pattern Function

16:66 Gearbox

Descrambler

Decoder

Sync Detect

66:16 Gearbox

Scrambler

Block Gen.

Coder

PMA

PMD

1616

Insert patterns at gearbox

Insert patterns at scrambler

Test here (or wrap only)?

BER Rx BER Tx

IEEE 802.3ae 3/12/2001


Proposed Test Sequence• Use existing 1 + x39 + x58 scrambler

– Seed register with defined value– Run for N bits (propose N= 216)

• Allow non-zero scrambler data inputs for additional flexibility– Reset scrambler & repeat

• Can use scrambler data input to reset its state (pseudo-seed)• Seed can be set via management registers

• Seed chosen to stress:– Maximum run-length– Minimum transition density– Maximum baseline wander

• N arbitrary, but …– Choose power of 2 for easy implementation– Choose N < memory depth of typical BERT

• Periodically resetting the scrambler implies the pattern is no longer “random”

IEEE 802.3ae 3/12/2001


Test Pattern Structure• Select a subset of the 258–1 PRBS using appropriate seed• Map the test pattern into the payload of the 66-bit blocks• Repeat the test pattern

N-bit Test Pattern (« 1017)

64b data0 1 64b data0 1 64b data0 1…

66b blocks

1 + x39 + X58 PRBS

3x1017 bits

IEEE 802.3ae 3/12/2001


Test Pattern Generation• Seed the scrambler• Apply, short, repetitive data pattern (e.g. all zero’s)• Apply pseudo-seed after N bits to transition to pattern beginning• Repeat

Seed …

Time

InputData Data p-Seed Data Data … p-Seed Data Data

S0 S1 S2 S38 S39 S56 S57

++Input

Output

Seed …Output

Test Pattern Test pattern … Test pattern

N-bit test pattern

« N bits

IEEE 802.3ae 3/12/2001


Example• Choose 1 + x6 + x7 PRBS,

– N= 16-bits– Pattern = 0 1 1 1 1 1 1 1 0 0 0 0 0 0 1 0 (longest run-length)

• Initial Seed = 1 0 1 0 1 0 0• To force scrambler to repeat the 16-bit pattern:

– “Data” = 0 1 1 1 0 0 1 0 0 0 0 0 0 0 0 0

• ∴∴∴∴Seed= 1010100, Pseudo-seed= 0111001• For Mth-order scrambler, need M-bits to reset the

scrambler

7bits reset the scrambler All zeros otherwise

IEEE 802.3ae 3/12/2001


Error Detection• Only using a subset of the full 258–1 sequence• Self-synchronous descrambler will generate “errors”

at pattern boundary– “Errors” are deterministic due to pattern mismatch

• The “error” pattern at the descrambler equals the “data” pattern used to reset the scrambler to generate the test pattern

– Can be taken into account to compute real error rate– Increases somewhat the complexity at the error detector

IEEE 802.3ae 3/12/2001


Pattern Characteristics• Compare proposed pattern with a 216 –1 PRBS

– PRBS choice is arbitrary– Want “random” pattern of ~216 length for comparison– 1+ x + x3 + x12 + x16 is convenient choice

• Evaluate– Running disparity– Transition density– Autocorrelation– Power spectral density– Baseline wander

IEEE 802.3ae 3/12/2001


Running DisparityNomenclature• “216–1 PRBS”:

– 216 bits long (one cycle + 1 bit)

– 1 + x + x3 + x12 + x16

• “258–1 PRBS”:– 216 bits long

(« one cycle)– 1 + x39 + x58

– Seed chosen for max run-length ~8kb from pattern beginning

0 1 2 3 4 5 6 7x 104

-150

-100

-50

0

50

100

150

200

250

300

350

Time (UI)

Run

ning

Dis

parit

y

258-1 PRBS216-1 PRBS

IEEE 802.3ae 3/12/2001


Transition Density• Transition density

averaged over 200 UI• 216–1

– 16 UI max run-length– 50% average density– 38% minimum density

• 258–1– 58 UI max run-length– 44% average density– 3% minimum density

0 1 2 3 4 5 6 7x 104

0.3

0.4

0.5

0.6

0.7

Tran

sitio

n D

ensi

ty 216-1 PRBS

0 1 2 3 4 5 6 7x 104

0

0.2

0.4

0.6

0.8

Tran

sitio

n D

ensi

ty

Time (UI)

258-1 PRBS

IEEE 802.3ae 3/12/2001


Autocorrelation

• Random data = delta function

• Full PRBS closely approximates random data

• Partial PRBS more correlated than random data

0 1 2 3 4 5 6x 10

4

-0.1

-0.050

0.050.1

Aut

ocor

rela

tion

216 - 1 PRBS

0 1 2 3 4 5 6x 10

4

-0.05

0

0.05

0.1

0.15258 - 1 PRBS

Time (UI)

Aut

ocor

rela

tion

IEEE 802.3ae 3/12/2001


Power Spectral Density• Increased low

frequency content in partial PRBS pattern

• Tones due to correlation in sequence

0 0.05 0.1 0.15 0.2-10

-5

0

5

Pow

er S

pect

ral D

ensi

ty (d

B/H

z)

0 0.5 1 1.5 2-30

-20

-10

0

Relative Frequency

258-1216-1

IEEE 802.3ae 3/12/2001


Baseline Wander

0 0.5 1 1.5-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time (UI)

Am

plitu

de

216-1 PRBS

DJσσσσ= 0.004,DJ-pp= 0.026Total ISI= -0.33 dB, Penalty= -0.03 dB, BLWσσσσ= 0.02442

0 0.5 1 1.5

-1

-0.5

0

0.5

1

Time (UI)

Am

plitu

de

258-1 PRBS

DJσσσσ= 0.007,DJ-pp= 0.089, Min. PW= 0.911Total ISI= -0.88 dB, Penalty= -0.62 dB, BLWσσσσ= 0.04551

IEEE 802.3ae 3/12/2001


|Amplitude| Histogram (216–1 PRBS)

0.9 1 1.1 1.20

500

1000

1500

2000

2500

3000

3500

Relative Amplitude0.95 1 1.05

0.0010.0030.01 0.02 0.05 0.10 0.25 0.50 0.75 0.90 0.95 0.98 0.99

0.9970.999

Relative Amplitude

Prob

abili

ty

Normal Probability Plot

IEEE 802.3ae 3/12/2001


|Amplitude| Histogram (258–1 PRBS)

0.6 0.8 1 1.2 1.40

1000

2000

3000

4000

5000

6000

7000

8000

Relative Amplitude0.8 0.9 1 1.1 1.2

0.0010.0030.01 0.02 0.05 0.10 0.25 0.50 0.75 0.90 0.95 0.98 0.99

0.9970.999

Relative Amplitude

Prob

abili

ty


“tails” in distribution

IEEE 802.3ae 3/12/2001


Alternate 258–1 PRBS Segments

• “258–1 PRBS”:– 216 bits long

(« one cycle)– 1 + x39 + x58

– Seed chosen for run-length of 58 ~8kb from pattern start

• “258–1 Alternate”– 216 bits long

(« one cycle)– 1 + x39 + x58

– Seed chosen for run-length of 50 ~8kb from pattern start

0 1 2 3 4 5 6x 104

-200

0

200

400

600

Run

ning

Dis

parit

y

Time (UI)

0 0.5 1 1.5 2 2.5 3x 104

0

0.2

0.4

0.6

Tran

sist

ion

Den

sity

Time (UI)

IEEE 802.3ae 3/12/2001


Baseline Wander

0 0.5 1 1.5

-1

-0.5

0

0.5

1

Time (UI)

Am

plitu

de

258-1 PRBS

DJσσσσ= 0.007,DJ-pp = 0.089, Min. PW = 0.911Total ISI = -0.88 dB, Penalty = -0.62 dBBLWσσσσ = 0.0455, BLWpp = 0.365

0 0.5 1 1.5-1

-0.5

0

0.5

1

Time (UI)

Am

plitu

de

258-1 PRBS (Alternate)

DJσσσσ= 0.005,DJ-pp = 0.036, Min. PW = 0.964Total ISI = -0.39 dB, Penalty = -0.05 dBBLWσσσσ = 0.0255, BLWpp = 0.17

IEEE 802.3ae 3/12/2001


Baseline Wander

0.8 0.9 1 1.1 1.2

0.0010.0030.01 0.02 0.05 0.10 0.25 0.50 0.75 0.90 0.95 0.98 0.99

0.9970.999

|Amplitude|

Prob

abili

ty

258-1 PRBS

0.9 0.95 1 1.05 1.1

0.0010.0030.01 0.02 0.05 0.10 0.25 0.50 0.75 0.90 0.95 0.98 0.99

0.9970.999

|Amplitude|

Prob

abili

ty

258-1 PRBS (Alternate)

IEEE 802.3ae 3/12/2001


Alternate “Data” Inputs

• “0000… data”– Seed chosen for

max run-length ~8kb from pattern start

– Data input to scrambler all zeros

• “1000… data”– Seed chosen for

max run-length – Data input to

scrambler = 1 + 63 zeros

– 64-bit data pattern repeats

0 2 4 6 8x 104

-200

0

200

400

Run

ning

Dis

parit

y 0000... data1000... data

0 2 4 6 8x 104

0

0.2

0.4

0.6

0.8

Time (UI)

Tran

sitio

n D

ensi

ty

IEEE 802.3ae 3/12/2001


Summary• Use existing scrambler / descrambler to generate and

check test patterns• Wide variety of pattern characteristics available

– Select long PRBS segments using short seed values• Pattern can be set via management registers

– New patterns can be defined in the future without modifying hardware

• Cost: increased complexity in the pattern checker

Backup Material

IEEE 802.3ae 3/12/2001


Stressed Eye

0 0.5 1 1.5-1

-0.5

0

0.5

1

Time (UI)

Am

plitu

de

K28.5 + Random 8B/10B Data

DJσσσσ= 0.030,DJ-pp = 0.084, Min. PW = 0.986Total ISI = 3.01 dB, Penalty = -2.84 dB

0 0.5 1 1.5-1

-0.5

0

0.5

1

Time (UI)

Am

plitu

de

258-1 PRBS

DJσσσσ= 0.028,DJ-pp = 0.089, Min. PW = 0.981Total ISI = -2.99 dB, Penalty = -2.76 dB

IEEE 802.3ae 3/12/2001


0 1 2 3 4 5 6 7 8x 104

-200

-100

0

100

200

300

400

500

600

700

800

Time (UI)

Run

ning

Dis

parit

y

OC-192 CID Pattern

16kb PRBS32kb PRBS

72 1’s72 0’s

16kb PRBS

A1/A2

OC-192 “CID” Pattern• 192 bytes A1• 192 bytes A2• 64 bytes C1• 128 bytes of “stuff”

(return disparity to 0 with 50% transition density)

• 16kb PRBS(x10+ x7+1)

• 72 zeros• 32kb PRBS

(x15+ x14+1)• 72 ones• 16kb PRBS

(x10+ x7+1)

IEEE 802.3ae 3/12/2001


Running Disparity

0 1 2 3 4 5 6 7 8x 104

-200

-100

0

100

200

300

400

500

600

700

800

Time (UI)

Run

ning

Dis

parit

yOC-192 CID

258 - 1 PRBS

IEEE 802.3ae 3/12/2001


0 1 2 3 4 5 6 7x 104

0

0.2

0.4

0.6

0.8258 - 1 PRBS

Time (UI)

Tran

sist

ion

Den

sity

0 1 2 3 4 5 6 7 8x 104

0.2

0.3

0.4

0.5

0.6

0.7OC-192 CID Pattern

Tran

sist

ion

Den

sity

Transition Density• Transition density

averaged over 200 UI• OC-192 CID

– 72 UI max run-length– 50% average density– 21% minimum density

• 258–1– 58 UI max run-length– 44% average density– 3% minimum density

IEEE 802.3ae 3/12/2001


Baseline Wander

0 0.5 1 1.5

-1

-0.5

0

0.5

1

Time (UI)

Am

plitu

de

OC-192 CID Pattern

DJσσσσ= 0.013,DJ-pp= 0.162Total ISI= -2.25 dB, Penalty= -1.76 dB, BLWσσσσ= 0.06953

0 0.5 1 1.5

-1

-0.5

0

0.5

1

Time (UI)

Am

plitu

de

258-1 PRBS

DJσσσσ= 0.007,DJ-pp= 0.089, Min. PW= 0.911Total ISI= -0.88 dB, Penalty= -0.62 dB, BLWσσσσ= 0.04551

IEEE 802.3ae 3/12/2001


Baseline Wander (OC-192 CID)

0.5 1 1.50

0.5

1

1.5

2

2.5

3x 104

Relative Amplitude0.6 0.8 1 1.2 1.4

0.0010.0030.01 0.02 0.05 0.10 0.25 0.50 0.75 0.90 0.95 0.98 0.99

0.9970.999

Relative Amplitude

Prob

abili

ty


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