A potential bug discovered in Apple's latest iOS 9 release appears to be impacting certain apps running on iPhone 6s that tap into compass and gyroscope data, in some cases affecting key assets that render some features unusable.
reader Frank experienced the problem first hand with popular stargazing app Sky Guide, which relies on iPhone's advanced sensor suite to power an augmented reality function that transforms the device into an interactive map of the night sky. Under normal conditions, users point their iPhone up toward the sky to see an onscreen view of stars, planets, constellations and more, but on iPhone 6s running iOS 9 -- including the latest iOS 9.0.1 update -- the map drifts uncontrollably.
Developer Fifth Star Labs confirmed issues affecting Sky Guide's "Compass" feature are limited to iPhone 6s and do not extend to older hardware. Other augmented reality titles relying on data generated by iPhone's digital compass, three-axis gyroscope and accelerometer are also seeing problems, but certain apps like Apple Maps function correctly, suggesting the issue lies in a faulty iOS API. Fifth Star Labs is currently working on a fix.
Apple faced similar sensor difficulties in 2013 when iPhone 5s owners reported faulty readings from iOS 7's Compass app. At the time, some assessments claimed Apple failed to properly employ an appropriate firmware calibration bias when it switched from accelerometer supplier STMicroelectronics to Bosch.
Extremely sensitive components like those employed in iPhone are notoriously difficult to integrate due to wide ranging hardware variance and bias specifications that differ by type and manufacturer. A seemingly minor discrepancy might result in pronounced deviations for apps tapping into iPhone's data feed.
According to iPhone 6s and 6s Plus teardowns, the handsets use the same InvenSense 6-axis gyroscope/accelerometer chip and Bosch Sensortec 3-axis accelerometer module found in last year's iPhone 6 lineup. Upgraded from last year is the M9 motion coprocessor, now embedded in Apple's A9 SoC, which acts as a data hub for iPhone's various sensors, including the accelerometer, compass, gyroscope and barometer.
Update: Sky Guide has been updated with a workaround for the Compass feature issue.