Jun 27, 2013

Separating You from Your Phone

posted by Bryon Moyer

In high-school physics class, we did an experiment. It’s so crude by today’s standards, that I feel like something of a fossil as I recall it, but here goes. We had a ticker-tape kind of thing that would make a mark on a paper tape as you pulled the tape through. It marked at a constant frequency, so if you pulled the tape faster, the dots were farther apart. So dot spacing became a measure of speed.

The experiment consisted of two parts. In the first, we held the tape and walked a distance, swinging our arms like normal. In the second, we walked the same distance at the same speed, but holding our arms still.

In the first case, the dots tell a tale of acceleration and deceleration, repeated over and over as our arms moved forward and then backward. The second case showed no such variation; speed was consistent. But the trick was, if you averaged the speeds on the first one, you ended up with the exact same speed as the second one*. Which is obvious with just a little thought: it’s the speed we were actually walking.

This was an early case of, well, not sensor fusion, but, how about if we call it “implied signal extraction.” In this case, there was only one sensor (the tape), which is why there’s no fusion. But in modern times, such extraction might involve fusion.

Here’s the deal: the tape was directly measuring the speed of our hands, when what we were really interested in was the speed of our moving bodies. By averaging the hand movements, we were able to extract the implied body movement signal out of a raw hand movement signal that contained lots of potentially misleading artifacts.

This is happening in spades today in the navigation/orientation business. This will be obvious to the folks that have been trying to manage the problem for a while, but the rest of us may not realize how tough this is. We expect that, with our phones, we now have a way to navigate simply because our phone goes with us.

But put your phone in your hand. Now extend your arm forward: according to the phone, you just moved forward a foot or so. But you didn’t: your arm moved your phone forward; you didn’t go anywhere. Now put your phone in your back pocket, display to the outside. According to your phone, you just turned around. But you didn’t: you turned your phone around as you put it in your pocket. (Heck, the phone might even think you’re standing on your head if you put it in your pocket upside down.)

This drives at the art of orientation-to-trajectory management, a topic I discussed with Movea’s Tim Kelliher at Sensors Expo, and something Movea is working on. Unlike my high school scenario, where, if done right, we’re essentially averaging out a well-controlled sinusoidal movement, our phones go all over the place while we stand in one place. We pick it up, turn it around to orient it properly, switch hands, drop it, put it into one pocket or another, wave it randomly when we try to swat away that bee with our phone-holding hand.

Oh, and we can also do all of this while walking. Or running. Or dancing. Or running in random directions while we try to escape that bee, hands still aflail.

When you think about it, it’s got to be really hard to evaluate all of the sensor inputs on the phone and extract from that a signal that describes how the phone holder is moving. The more I think about it, the more I feel like I would have no idea how to start. Presumably some heuristics would be involved, but even then, it’s not obvious.

For instance, if the proximity sensor is firing, then you might assume that you’re probably on a call, and so conclude that the phone is stationary with respect to the body, up by your ear. That might be right 90% of the time, but then some goofball will, just for sh…ucks and grins, move the phone sultrily up and down along his or her body, keeping it close. The “on a call” heuristic would then decide that we’re walking up and down hills.

So when solutions to this problem are finally announced, I can imagine the aforementioned goofball types to try all kinds of things to see if they can fool the system. Typical silliness, but it also provides clues about how the algorithm works.

For the rest of us, well, let’s not take it for granted. This is a hard problem, and any effective solution will have been hard won.

 

*It actually didn’t work for me; my teacher declared, in frustration, that I needed to learn to walk a consistent speed. Not sure if I’ve mastered that yet; it’s not high on my bucket list…

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Jun 26, 2013

Simpler CDC Exception Handling

posted by Bryon Moyer

For static timing analysis, it’s a concept that goes back years. You get a bunch of violations, and then you have to decide which ones represent false paths or multi-cycle paths and create “exceptions” for them. Tedious.

Well, apparently formal analysis can have the same issue. Only here they’re referred to as “waivers,” according to Real Intent. If you run analysis and get a long list of potential violations, you have to go through the list and, one by one, check them for “false positives” and mark them as such. Time-consuming and error-prone. And tedious. Especially when working on large-scale SoCs (so-called “giga-scale”).

In their latest release of Meridian CDC, which does clock-domain crossing verification, Real Intent has provided a different way of handling this: provide more granular control over the run parameters in the form of rules or constraints that can be successively refined.

Using the old method, if a particular over-reaching aspect of analysis caused 100 false positives, you’d have to find all 100 and “waive” them. With the new approach, when you find the first one, you make the refinement, and then, with a rerun of the analysis, the one you found and the other 99 all disappear. OK, not disappear per se, but they’re grouped together as not being an unexpected finding. You can also review that list to make sure nothing snuck through. (This is a simplification of a more sophisticated overall process, but it captures the essence.)

This may take some iterations, but in the end, you can have a clean run with no exceptions, and the way you got there is less likely to have involved a mistake here or there.

You can find out more about Real Intent’s latest Meridian CDC release in their announcement.

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Jun 20, 2013

Extreme Compilers for Extreme Architectures

posted by Bryon Moyer

ACE calls them “extreme architectures.” These are the processors that your mother told you to avoid because they’re just too darn hard to support. You can come up with the niftiest hardware features, but who’s going to figure out how to turn C code into something that will take advantage of them?

Well, ACE would say, “Don’t listen to your mother.” Their CoSy tool (I keep wanting to pronounce this “Co-Sigh,” you know, kind of like when you both lay back and realize that you both have something you need to talk about… but actually, ACE pronounces it “cozy”…) can take bizarre architectures and help you generate a compiler than optimizes the code it generates from a C program.

Where do you find these processors? In those dark alleys your mother told you to avoid? Perhaps… There might be one in that headset that that shady character is wearing. Don’t ask to take it apart and check; take our word for it.

But deeply-embedded processors that look nothing like the kind your mother likes, resembling them only in that they run code; they are found in the dark recesses of systems where every cycle counts for very specific functions. Like audio. Or video or communications or… well, your imagination is the limit.

Down there, you can sneer at power-of-two bit widths. You want precisely 11 bits? 17 bits? 19 bits? (These are prime examples…) You can do it, and CoSy will help you produce a compiler that allows a C program to use that data. You can also set custom alignment.

And the supported architectures don’t have to be on some “Here are the supported bizarre architectures”  list. If you build your own via ARC (now Synopsys) or Tensilica (now Cadence), for example, you can still use CoSy to generate the compiler.

You can find out more about their latest edition in their announcement.

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