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A Case for Custom Silicon in Enabling Low-Cost Information

Technology for Developing Regions

Z. Foo, David Devecsery, T. Schmid, N. Clark, R. Frank, M. Ghaed, Y. Kuo,

Lee, Y. Park, Z. Renner, N. Slottow, V. Vinay, M. Wieckowski, D. Yoon,

C. Schmidt , D. Blaauw, P. Chen, and P. Dutta

The University of Michigan

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Motivation

• Recent studies show benefits of information in developing regions

• Avaaj Otalo– Mobile-phone-based interactive voice forum– Users found value listening to questions and answers

• Digital Green Project– Disseminate agricultural information through video– Large increase in adoption of agricultural practices

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Motivation

• Talking Book Project– Provide on-demand access to information from local experts– Information pre-loaded onto devices, and re-programmed in field– Farmers showed a significant increase in crop production

• Question: Why aren’t these devices more popular in developing regions?

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Commodity Devices Not Sufficient• Radio

– No replay capability– No indexing– No on-demand information

• Voice Recorder– No indexing– Information distribution difficult

• Cell Phone– Too expensive - $20-$40– Running cost too high - $.10-$.30/min. in rural Africa– High power draw– Connection unreliable

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Custom Devices Still Not Sufficient• Lifeplayer

– Provides data recording, playback, indexing, communication

– Costs around $100– Very large

• Talking Book– Similar functionality to Lifeplayer– Scaled way down

• Hand-held• Costs between $20 and $35• 2 - 3 day lifetime on AA batteries

Source: lifelineenergy.org

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Our Goal

• Design a custom device:– Provide recording, playback, communication, data

indexing– < $10– Reduce upkeep cost to user

• Case Study: Redesign Talking Book

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Improving The Talking Book

• Reduce costs with– Custom silicon integration– Flatter memory hierarchy – Unconventional communication

• Will reduce cost to $10 and power by 6x

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Use Custom Silicon

• Aggressively integrate into custom silicon• Eliminate discrete components

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Integrate to Chip

• Speaker amp• Voltage regulators• Oscillators

– One off chip crystal– Inexpensive, and slow

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Memory Hierarchy• Old Memory Hierarchy

• Goals of new system:– Minimize Costs– Allow for large code bases– Easy for programmers

Core

ExternalNOR Flash

Internal Flash

ExternalSD Card

Internal RAM

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Minimizing Memories

• Use only one NAND Flash– Lower power– Less expensive

• NAND Flash– Chips wear out– Not fault tolerant– Slower– Requires software FTL– Uses cache

– Improve performance– Reduces flash wear

Software FTL

NAND Flash

Cache

Microcontroller

Core

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Custom Cache• 4-way set associative• 128 KB memory• Cache must use core

– Interrupts fetch data– Similar to MMU

• Pinned region– Stops critical code from missing– Allows real-time guarantees

Software FTL

NAND Flash

Cache

Microcontroller

Core

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Move Interfaces On-Chip• Push button interface

– Expensive - $1– Requires membrane switch-pad– Mechanical failure

• Replace with Capacitive Sensors:– Low chip area – Nearly no cost– Built into PCB– No physical system

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Communications

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Communications

FM Radio

• Long range voice distribution

• Digital data through RDS sub-band

• Download information over night

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Communications

FM Radio

Inductive Link

• Replaces USB• Wireless peer to peer• 500Kb/s• Integrated into PCB• Minimal hardware cost

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Communications

FM Radio

Inductive Link

Cell Phone

• On-demand information download

• Directly download voice

• Digital data with FSK modulation– Firmware Updates

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Bill of Materials - ComponentsComponent Name Cost Speaker Inductor $0.0245 Speaker Capacitor $0.0090 Linear Regulator Cap $0.0107 Step-Up Converter Cap (Type 1) 4

$0.0027

Step-Up Converter Cap (Type 2) 2

$0.0246

Chip Area $0.7600 Total Chip Cost $0.8315

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Bill of Materials - BoardComponent Name Cost Chip $0.8315 Speaker $0.7783 Headphone Jack $0.0232 Microphone $0.0935 PCB $1.0050 NAND Flash $2.0000 Radio $1.0395 Total Board Cost $5.7711

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Bill of Materials - System

Component Name Cost Board $5.7711 Casing $1.0000 Test & Assemble $1.0000 Total System Cost $7.7711

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NRE Costs

• Custom silicon equal COTS 70k units• Custom silicon < $10 at 400k units

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Power Costs

• 2 Week battery lifetime on 2 AA Batteries• Overall 6x power reduction

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Summary

• Current devices are not sufficient• Custom silicon:

– Gives similar functionality to old Talking Book– Allows entire system on three chips– Reduces all costs to within goals

• Custom silicon presents a viable option for large-quantity developing world products

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Low-Power Core

• Use ARM Cortex-M0 processor– 50MHz core clock– ARM v6m ISA

• 32-bit performance • 16-bit instruction size

– <10% of total chip energy in active mode– Decodes, timescales, & plays audio real time

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Cell Phone Issues

• Use More Power• Stuff about why not good