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What’s Next for BoW in 2024

(Optical, IoT and Memory Interfaces)

Shahab Ardalan, VP Engineering & Co-Founder, Enosemi

Kevin Donnelly, VP Strategic Marketing, Eliyan

Kash Johal, CEO & Founder, YorChip

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Bunch of Wires (BoW) Key Features

  • Open PHY and Link Layer specifications�for die-to-die (D2D) parallel interfaces
    • State-of-the-art performance metrics
      • Up to 32Gb/s/line, <0.5pJ/bit, <8ns bus-to-bus �latency
    • Compatible with a wide range of packages,�IC processes, and cost/performance design�points

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  • BoW specifications enable D2D interfaces to be optimized to their host chiplet products
    • Specifications are architected to be minimalist in their required features while supporting interoperability

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What’s Next for BoW – BoW 2.1

  • To help enable the Open Chiplet Economy, BoW is evolving to meet the requirements of new applications
    • Higher performance for AI and Edge applications
    • Lower cost for IoT applications
  • Working now on additions for an upcoming BoW 2.1 release with spec extensions related to three focus areas:
    • Optical
    • Memory
    • IoT

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Motivation to have Optical D2D Interface

  • Where do we need optical interconnect?

[J. Campenhou, ISSCC 2022]

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Optical Chiplet

  • Shifting Optical Engine (E2O/O2E) into the ASIC package

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Supporting Optical Chiplet using BoW

  • Direct Driving Optical Engine using existing BoW IP
  • No retiming at the optical chiplet

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ASIC

ASIC

B

o

W

-

T

X

B

o

W

-

R

X

E

Q

O2

E

T

I

A

CK

D

E

2

O

E

Q

D

R

CK

D

Chiplet-A

Chiplet-B

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0dB

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Asking for participation

  • Parameters to consider
    • Latency
    • Forwarded Clock quality (Jitter)
    • Quality of Data Delivery
      • RF Loss
      • ISI
      • Jitter
    • How to handle power down
    • How to address side channels

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Motivation to use D2D Interfaces for Memory

  • The ”Memory Wall” is limiting the performance of Generative AI ASICs
  • The top factor driving recent performance increases is due to DRAM bandwidth boosts
  • Driving factor is BW/mm metric on ASIC edges (beachfront)
  • D2D interfaces have the potential to dramatically improve memory BW/mm for ASICs

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D2D Signaling Technology Types

BoW 1.0 and UCIe 1.1

BoW 2.0

Memory PHYs

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Two Example D2D Use Cases for Memory

1) D2D use case Example

  • 2 DDR5 DIMMs
  • Read BW 128 GB/s
  • R/W BW ratio 2x
  • CMD, Ctrl, Sideband

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2) D2Mem use case example

  • 1 HBM4 DRAM example
  • DQ Read or Write BW 2 TB/s
  • Support for ECC traffic
  • Control O/H 25%
  • Beachfront < 10mm

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Potential BoW 2.1 Spec Changes to Support Memory

Potential Spec Changes by Use Cases

1) D2D �Logic-to-Logic

2) D2Mem �Logic-to-Memory

BoW PHY Changes

Possibly none �(asymmetric Read vs Write BW already allowed)

Yes (Ex: dynamic bidi)

Link Layer Changes

Likely new interface profiles and possibly bus variants; possible Link Layer changes to support asymmetry

Likely new interface profiles for each new memory type

Configuration Doc

Yes (per Protocol?)

Yes (per memory type)

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Bunch of Wires addendum to support IOT

ESPECIALLY FOR IOT & SENSORS

NEED LOW COST

<20% AREA

NEED LOW POWER

4 LANES VS 32

SIMPLE DEVICE

NO PLL REQUIRED

FLEXIBILITY

RX & TX

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CLK Rates

  • Target is to support 1G as default and 500MHz at low end – no upper limit specified
  • We have seen interest in even 90nm for Mixed Signal IP for IOT so lower CLK rate is desirable
  • BOW supports 1G CLK 2G operation as minimum so just clarify that as default start up ? Then negotiate to alternate speed

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Benefits /Drawbacks of IOT proposal

Advantages

Drawbacks

Half-Link's data buses are in close proximity to the centralized clock, optimizing synchronization and signal integrity.

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A symmetrical design can enable more layout sharing between TX and RX PHYs.

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Enables dual purpose TX and RX PHYs.

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Enable flexible RX/TX PHY signaling scheme

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Device setup is simplified – Just works once set

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Reduces PLL requirement for Device

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Reduces Power & Cost

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Conclusion

  • Lots of ongoing work to add to the BoW specification, including new features for memory & IoT
  • Get involved and join the workstream meetings!
  • Look for the BoW 2.1 release later in 2024

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