Bizarre Droid Auto-Focus Bug Revealed

itwbennett writes "Pity the poor engineer who had to find this one. One of the more interesting of the handful of bugs that have appeared since the launch of Verizon's Droid smartphone has to do with the on-board camera's auto-focus. Apparently it just didn't work. And then suddenly it did. Naturally, this off-again, on-again made the theories fly. But the real reason for the bug was revealed in a comment on an Engadget post by someone claiming to be Google engineer Dan Morrill: 'There's a rounding-error bug in the camera driver's autofocus routine (which uses a timestamp) that causes autofocus to behave poorly on a 24.5-day cycle,' said Morrill. 'That is, it'll work for 24.5 days, then have poor performance for 24.5 days, then work again. The 17th is the start of a new 'works correctly' cycle, so the devices will be fine for a while. A permanent fix is in the works.'"

Comments

When Signed/Unsigned Strikes

[eldavojohn]

It's all over the comments on the engadget page but since 2^31 milliseconds is about 24.5 days, it's highly probably we're dealing with a very classic not so funny sign extension bug here. So if I may presume the real problem, it's that autofocusing depends on catching timestamps from the system to know how long it's been since the last sampling in order to adjust the lens and check for accuracy. It's casting this to a signed 32 bit variable which means that during the 24.5 days it is miscast to a negative number, thus breaking the algorithm when it measures time deltas and causing it to mis focus before snapping the picture.

The patch is simple, make that signed int something like an unsigned long or truncate it properly. Hopefully we're not waiting long.

Re:When Signed/Unsigned Strikes

[BitZtream]

Most cameras do, they just don't use a RTC value to do so.

You don't want it continually focusing, you want it to focus then wait a bit otherwise it'll bounce all over the place. You check the distance, wait a moment, and check again, is it close to the same? If so use that as your focal length, other wise you'll probably end up never in focus cause you'll be using all the various raw values given to you by the sensor. This is likely input averaging to get a smooth value and throw out bad samples.

Take a look at the raw input values provided by most game controllers, try to hold an analog stick in one spot and not get jitter in the raw values, unless the device itself is averaging you won't got a solid result. Plug a xbox controller into your PC and use the Windows control panel (if you're using windows, never plugged a joystick into a unix box myself) to see how jumpy it is.

A sensor measuring the environment outside, in someones hand is going to bounce around like a mad man, so it has to be smoothed out somehow.

Re:Bigger bugs afoot...

[DeadCatX2]

Exchange works great for me. So does navigation. I had no problem charging my phone with my netbook's USB port. I did, however, notice that changing the orientation can cause not-yet-applied settings to be forgotten (happened to me while setting up Exchange).

I don't have any Bluetooth stuff so I can't comment on Bluetooth support, but I imagine it will improve. Bluetooth seems like a very temperamental protocol. That said, hands-free Bluetooth voice dialing is actually a showstopper for a lot of important business types, so that should get fixed right away.

If you don't like the native Contacts application, I'm sure you can find some others. Personally, I use the Favorites tab of the Contacts widget, and that handles 95% of the times I want to make a phone call in two clicks.

Finally...Motorola made the phone, not Google.