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by inoop
4664 days ago
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I doubt it's for GPS assistance. Motion sensors can be used to suppress Wi-Fi scanning and/or GPS localization during the roughly 89% of the time humans are not moving. Remember, phones continually scan for new Wi-Fi APs in the background even when the screen is off. On modern phones with a/b/g/n chipsets (32 channels to scan) and energy-expensive CPUs (i.e. Exynos) this takes a huge amount of power. Motion sensors themselves are really energy-cheap but the main CPU needs to be on to sample them, which basically means that if you want continuous mobility detection you're going to burn through your battery pretty quickly, which is why it isn't used much. You can do some CPU duty-cycling, but wake-up and suspend overhead is pretty bad and can amount to as much as 50% of the total energy spent. I haven't done any measurements on an iPhone, but a GS2 Exynos 4 is a terrible energy drain, while an something like an OMAP 4460 (e.g. Galaxy Nexus) is much more efficient. By offloading mobility detection to a separate chip you can bring down the overhead to tens of mW. The fact that you can use it as a step counter for jogging is just icing on the cake :) |
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It's a coprocessor not a sensor, so it may operate independently of the CPU as far as continuously sampling the motion sensors is concerned. Presumably that requires much less power to do so.
Of course it will used to augment/supplement GPS.