Air presentation at NMI verification workshop

1. Low-Power Verification, the Way
Functional + Physical Low-Power Silicon Verification
David Tester, Founder & CTO
26 February 2009

2. What are the Low-Power Verification Questions?
How can you prove low-power silicon implementation of a system?
Disruptive products demand system-level optimizations
- Low-Power is no exception and requires …
- Example: airwave1 and low-power GPS optimization
- Today we will not discuss GPS or system verification!
Let‟s consider an alternative question:
“How did you prove (verify) the silicon implementation of
that low power architecture? What are the challenges?”
Here are five … not in order and not an exhaustive list …
Q1. Lazy is OK. How do you know when you‟re done?
Q2. Did you survive (or avoid) the pain a PMK can offer?
Q3. How did you verify clock tree power consumption?
Q4. Multi-DVDD chips – Where EDA meets reality …
Q5. Is timing-optimized and power-optimized the same?
… but first let‟s have an advert for

3. GPS 101
Received Power is -130dBm (Maximum) … 20dB below Thermal Noise Floor!
Earth radius 6 km
3578
6378 km
m
0 0k Geo-stationary
191
Regional geo-stationary
augmentation satellites
km
20200 WAAS
Wide Area Augmentation System – USA
EGNOS
23222 km European Geostationary Navigation Overlay
System – Europe
GPS
6 orbital planes; 55° to equator Galileo
Orbit 14 hours (approx) Moon
Galileo 13300 km/h Approx. 400000 km
3 orbital planes; 56° to equator
GLONASS
GPS
3 orbital planes; 65° to equator Orbit 11 hours 58 minutes
13900 km/h
GLONASS
Orbit 11 hours 15 mins
14200 km/h

4. GPS with airwave1 silicon

5. The A Development Team
Air Headcount: 23 people
10x Employee Development
9x Contract Development Hugh Thomas
4x Non-Development Staff
CEO
David Tester Andy Heaton Stephen Graham
Co-Founder & CTO VP Operations & Development Co-Founder & VP Marketing
RFIC Design System Design ASIC Design Software Design
Staff Staff Staff Staff
Employee #1 (20 years experience) Employee #3 (20 years experience) Employee #4 (10 years experience) Employee #7 (20 years experience)
Employee #2 (20 years experience) Employee #1 (20 years experience) Employee #5 (15 years experience) Employee #8 (15 years experience)
Employee #6 (15 years experience)
Contract Contract Contract
Contract #1 (15 years experience) Contract #3 (20 years experience) Contract #8 (20 years experience)
Contract #2 (15 years experience) Contract #4 (20 years experience) Contract #9 (15 years experience)
Contract #5 (20 years experience)
2x Synopsys IC layout contractors
Board of Directors
Support Staff
Hugh Thomas CEO ex-CEO TapRoot 1x General Admin
1x Finance Manager
David Tester CTO
ex-CEO Andromedia (acquired Macromedia ‘99)
Kent Godfrey Pond Ventures
ex-CEO Frictionless Commerce (acquired SAP ‘06)
Michael Gera Pond Ventures
ex-CEO PortalPlayer (NASDAQ: PLAY)
Gary Johnson Independent ex-CEO S3 (NASDAQ: SIII)

6. History – Design, Verification, Schedule conflict
Hugh Thomas
CEO
David Tester Andy Heaton Stephen Graham
Co-Founder & CTO VP Operations & Development Co-Founder & VP Marketing
RFIC Design System Design ASIC Design Software Design
Staff Staff Staff Staff
Employee #1 (20 years experience) Employee #3 (20 years experience) Employee #4 (10 years experience) Employee #7 (20 years experience)
Employee #2 (20 years experience) Employee #1 (20 years experience) Employee #5 (15 years experience) Employee #8 (15 years experience)
Employee #6 (15 years experience)
Contract Contract Contract
Contract #1 (15 years experience) Contract #3 (20 years experience) Contract #8 (20 years experience)
Contract #2 (15 years experience) Contract #4 (20 years experience) Contract #9 (15 years experience)
Contract #5 (20 years experience)
Air tracks GPS satellites with RFIC
2x Synopsys IC layout contractors March „08
RFIC + FGPA platform
May „08
Air tracks GPS satellites with RFIC + FPGA
A1225 RFIC (v1) June „08
April „07 Air first PVT, confirms lab in Swindon
June „08
A1225 RFIC (v2)
A1250 single die GPS receiver
February „08
January „09
J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D
2006 2007 2008 2009
J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D
Electra Start-Up of the Year 2008
November „08
Gary Johnson joins Board of Directors
2x NASDAQ CEO (PortalPlayer & S3) IET Start-Up of the Year 2008
May „07 November '08
Prof Izzet Kale joins Technical Advisory Board
October „08
Engage with TSMC for silicon
Sept „06
Demonstrate GPS technology
July „08
Development starts!
June „06 Recruit external CEO
May „08
Air Inc + Ltd incorporated
May „06 Red Herring 100 Europe 2008
April „08
Series-A Termsheet
April „06 Exit stealth mode
Announce 1st product
January „08

7. Optimize for Power Everywhere, But Earlier is Better
Low power algorithms more efficient (for hitting targets) than optimized circuits

8. Quick Review on Where that Power is Consumed
Dynamic (switching) and static (leakage) power from DVDD to DVSS
Example circuit taken from:
http://www.dti.unimi.it/~liberali/papers/c63.pdf

9. When is “Low-Power” low enough? When to Stop?
Products need to get to market … Stop when you‟ve verified it‟s good enough
Can you spot the conflict between the following two statements?
“I‟d like the lowest possible power consumption, please”
“I‟d also like to get that product to market on time, please”
Do you have a power budget? When should verification STOP ?
Track and predict power performance at all levels of abstraction:
- Architecture / Algorithm / System Partitioning
- Pre-Synthesis RTL and Post-Synthesis Gates
- Pre-Layout and Post-Layout
“… but verification is never really complete…”
True
… what is the milestone for sufficient
confidence that power meets budget?

10. Less Complexity + Less Transitions = Lowest Power
Reduce depth of logic between flip-flops and switching activity to minimise power
How to verify switching
activity level on budget?
How to verify the original
complexity assumptions?

11. Routing Capacitance is the Enemy
Parasitic capacitance (from routing) significantly alters switching power of logic
How can you verify post-layout parasitic routing capacitance is acceptable?

12. Power Management Kit ... Handle with Care!
… rather like a chainsaw with all the safety features removed …
- Standard cell library assumes single DVDD supply voltage
- Power management library enables multiple voltage domains
- Voltage domain control cells – DVDD and DVSS switch
- P&R “optimisation” can pull cells from PMK library by mistake!
- Can simulation identify these problems?…
- Signal isolation cells (for crossing voltage domains)
- Must verify P&R didn‟t “optimise” these!
- PMK also adds more back-end DRC and LVS
verification issues simulation can‟t solve…

13. Multi-DVDD Silicon: Where EDA meets Reality …
Circuit level functionality that needs to be verified at RTL level
- DVDD functionality in “HEAD” and “FOOT” cells
… but DVDD not represented in logic simulation!
- How, and when, are cells instanced in the design?
- Manually by logic designer or layout team?
- Automatically by EDA tool? Do you trust it?
- Yet another task to verify before tape-out !!!
- Control signal active sense depends on cell used:
- Active low for PMOS but active high for NMOS
- Are control signal wired correctly?
- How many cells for each domain?
- “Power Aware” design flows try to plug the hole!
Example:
airwave1: 44x digital, 8x analog voltage domains

14. “Custom” Cells rather than “Standard” Cells?
„Optimized for Power‟ and „Optimized for Timing‟ are not always compatible
- Knowledge of “use” offer options for power optimized gates
- Power optimized and timing optimized are not always the same
Example
- Custom flip-flop used in airwave1 datapath
- Relaxed timing enabled >40% power improvement!

15. What‟s Your Methodology to Verify the Clock Tree?
Not all clock tree‟s are low power …
- Power depends on conflicting constraints: skew, rise time, load, etc
- CTS tools build functional but over-designed, high-power clock trees
- Can‟t verify power until P&R started ... but is that too late for market?
- Clock tree can pass functional verification but fail power verification!
Example:
airwave1:
400+ clock domains
More a clock forest
than a clock tree ...

16. Post-Placement Optimization? Roll the Dice Again!
Development on-schedule and on-budget? P&R “optimization” can solve that…
“Here‟s the final netlist,
it meets the power spec‟s
and just needs to go through P&R”
- Pre-Layout gate level power estimates are estimates
- Routing capacitance impacts both timing and power
- P&R optimization resizes gates to close timing
… almost certainly ignoring circuit power
… so power estimates on pre-P&R netlist
are exactly that - estimates
Verification Issue:
How to verify post-layout power still hits
the target specification …
… and hit your schedule

17. Validation of Software Power against Power Budget
After the HW / SW partitioning is done, does the software hit it‟s power budget?
How to Estimate Software Power ?...
(… since hardware power is under control)
- CPU power consumed with vendor „example‟ code
- Actual power with real code in real environment?
Example Issues:
Cache RAM v Main RAM power executing code
Does any firmware exist yet that can be profiled?

18. “Blind Faith and Ignorance” or “Informed Decision”?
Don‟t forget to be paranoid about power, if you care about power
Low-Power can be broken anywhere:
- Architecture
- Hardware (RTL) or Software
- Logic Synthesis
- P&R and CTS
- Cell library and macros choices
- Process technology
Each step demands differing levels of verification activity,
but verification of power needs more than just logic simulation
and must include power budgets, circuit simulation and
… application of brain power …