[stevep98]

> Next, it has an intriguing “motion coprocessor”, which I think pretty much means you can use your 5S as a fitness tracker with almost no effect on your battery life.

My guess is that it's much more than this. It's for augmenting the GPS location with dead-reckoning, for places where the GPS location doesn't reach well, such as buildings or on subways, etc.

Accelerometers are already pretty sensitive - enough to provide an improvement on GPS-only devices. But, this new coprocessor will allow a much higher-resolution sampling of the accelerometer, and thus the integration (in the calclus sense) of acceleration into velocity and distance will be much more precise.

[inoop]

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 :)

[sjtgraham]

> 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.

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.

[inoop]

I meant that on current phones the main CPU needs to be on, which is why motion suppression isn't used much. Apple added a separate processor to handle the motion sensing, thus offloading the main CPU, and saving energy.

> Of course it will used to augment/supplement GPS. > Of course

What do you base this on? Could you give me an example where a separate motion processor would augment GPS?

[simonh]

Inertial navigation? It's an interesting idea, but I think if they were doing that, they'd have touted it in the presentation as an example of something they can do that nobody else is even thinking about. It's not like apple to miss an opportunity to try an distance themselves from the pack on their technical capabilities.

[rahoulb]

One thing I noticed is that they said the 5S is a "forward-thinking" device, implying that they've got more planned for it.

[derefr]

What I hope this really means is less battery drain for geofencing.