Experts At The Table: Building A Better Mousetrap

Low-Power Design sat down with Richard Zarr, chief technologist for the PowerWise Brand at National Semiconductor; Jon McDonald, technical marketing engineer in Mentor Graphics’ design creation business unit; Prasad Subramaniam, vice president of design technology at eSilicon; Steve Carlson, vice president of marketing at Cadence Design Systems, and David Allen, product director for power at Atrenta. What follows are excerpts of that conversation.

By Ed Sperling

LPD: How important is it to be green?
Zarr: In the past, when our customers plugged something into the wall they didn’t care. They pushed the problem off. But with some of the legislation, people are starting to care. No system is ever loaded 100% all the time. Even data centers are not always busy. Typically 50% to 80% of the power is wasted. They’re running at high speed and consuming power when they don’t need to be. But they’re not doing anything about it because it’s adding complexity or it’s adding cost. You’re designing the hardware, but someone is taking that and using in ways that you didn’t design it.
Carlson: I wrote a paper on the effects of virtualization. One of the things they would do in data centers is offload the servers, but the servers would have to go into standby mode when they’re not being used. They didn’t stand-by very well because they were never designed to stand-by. An improvement in the architecture at the macro level would be a big benefit, but people aren’t doing that unless they’re forced to do it or unless it becomes a competitive advantage.
McDonald: Where people have been investing the time—in the handhelds and at the micro level and device-level optimization—we’ve squeezed a lot of benefit out of that. Things can be made better, but a lot has already been done. At the macro level, almost nothing has been done.
Allen: The great thing about the handhelds is they’re proof points that it can be done. There’s a lot of work going on in the networking companies now, but you’ve got to start at the IC level. Once you’ve got the infrastructure there, then you can start layering on energy efficiency in the lighting, the HVAC in the data center and controlling of peak power.
McDonald: Cisco did a study in 2006 where they determined that if they saved 1% on the power for a network router it was the equivalent of taking tens of thousands of cars off the street. But when you’re designing it, no one cares. They just want to get it out the door and meet performance.
Zarr: Education is a big thing here. Designers are not educated in the vehicles to reduce the power consumption in their designs. It hasn’t been a priority for them.
McDonald: It’s also the delayed benefit. It’s not a benefit to the designer or even the company making the chip.

LPD: If it came down to hitting a deadline for getting a design out the door or cutting power, what’s the likely response?
Carlson: In the case of a very large printer company, it’s getting the chip out the door—even if it ultimately costs more money.
McDonald: Power is not really what most people care about up front. You care about the economics. You care about power only insofar as it affects the economics.
Zarr: It may have more of an impact as we go forward.

LPD: What happens if we trim the margin in designs? Do we gain power savings?
Carlson: There’s incredible waste. If you look at design methodologies for front-end design teams, there was a 5% margin. Now it’s typical to see 20% to 25% margin. One company we’re working with is going to use a 50% timing margin on the design for a battery-operated application. You start to explain what the impact will be on the overall logic architecture and the response you get is, ‘I hadn’t thought of that.’ You need to look at timing and power together. That’s where the real increases in margin occur.
Subramaniam: Margin is an issue, but it’s even more than that. Today we’re overdesigning chips because we are designing for the worst-case scenario that may never occur. So how do we take advantage of the process itself? You need to monitor the chip and lower your voltage accordingly. You’ve designed the chip for the slow corner, but you know that in normal conditions the chip is going to work much faster.

LPD: We’ve been adding cores and power domains on a regular basis. Now we’ve got a bunch of this stuff. How do you manage all these pieces?
Allen: You need to start at the architectural level. You can’t retrofit designs on the chip. There are a small number of power architects who can do this. They understand what the tradeoffs are, and from an EDA perspective you have to arm them with the right tools.

LPD: How small?
Allen: At ST there might be four. At TI there might be a half dozen. Maybe that’s enough. You don’t need a whole new power architecture for each derivative. You need a power architecture for the first one, and then you may get 30 or 40 derivatives out of that. But can every small company afford to have one of those guys? No. But big companies do have this expertise.
Carlson: There are sources of expertise to bridge the gap.
Allen: With external expertise, there’s a question of how much the design team learns.
Carlson: It depends on how you structure the engagement. If it’s a turnkey operation, they’re not going to learn much. But you can also teach them how to fish.

LPD: Do we ever get to the point where it’s no longer economical to do this stuff?
Subramaniam: You can probably go quite low on voltage for digital logic. We had a customer running digital logic at 600 millivolts. They could afford to do that because the chip runs at a very low frequency. If you’re willing to go with low performance, you can go to very low voltage on digital logic.
Allen: We’re not quite at the end of this road. Another thing to think about is how much charge is in a battery. That’s not really going to change that much. But there is still a lot of potential for architecture at the high end of the spectrum. Those guys can probably learn a lot.
Zarr: Even architectures that scale frequency will find benefit.

LPD: Is there a limit to how far down we want to go down the Moore’s Law roadmap, though?
Subramaniam: There is definitely a tradeoff. Only those with high-volume products will be willing to go to the next step.
Zarr: You never know until the next materials come out. They’re just continuing with strained silicon techniques and SOI.
Subramaniam: There are still a lot of designs done in 0.25 micron and 0.18 micron today. TSMC has not retired a single process since its inception. People will be willing to go back to older nodes if it helps them, but it doesn’t really help with power because they consume more power.

LPD: How do more restrictive design rules affect all of this?
Carlson: That will drive a renaissance in architecture. The process guys will quit solving the problem for you, and you have to be more clever about everything. You can’t just say you’re going to use the next-generation LP process and think you won’t have a problem with it.
Allen: There have been a number of times where the design guys said, ‘Leakage is going to kill us,’ and the process guys said, ‘Don’t worry about it.’ Then it scales to the next generation and it’s something else. The process guys may save us, but they won’t be able to save us forever.
Zarr: Somewhere along the line we’ll have to change materials, whether it’s carbon or something else. Everyone’s trying to avoid making that kind of investment.