[Dev] Sensor timestamp source (Tizen 2.3.2, Gear S2 EPK5 firmware)

Maxim Khitrov max at bhsai.org
Thu Dec 29 16:25:04 GMT 2016


Hi,

I posted about this on the developer forum and JIRA back in August,
but got nowhere. The original Gear S2 firmware used CLOCK_MONOTONIC
for sensor event timestamps. The next firmware (DPG1) changed this to
CLOCK_REALTIME. The new firmware (EPK5) that was released a few weeks
ago changed the source yet again, only this time I don't have a clue
what it's using and I can't find the relevant source at
https://review.tizen.org/git/.

Here's logcat output from a small native test program:

12-29 10:29:19.827 : CLOCK_MONOTONIC: 153936923042954
12-29 10:29:19.862 : CLOCK_REALTIME:  1483025359862936528
12-29 10:29:27.222 : [00] t=18446744073694551
12-29 10:29:27.222 : [01] t=225000(-18446744073.470)
12-29 10:29:27.222 : [02] t=465000(+0.240)
12-29 10:29:27.227 : [03] t=705000(+0.240)
12-29 10:29:27.227 : [04] t=946000(+0.241)

The first two lines are the current time values obtained using
clock_gettime, followed by 5 acceleration events at a rate of 250 ms.
What am I looking at? Yes, I get that the last four values are
relative times in microseconds (even though the docs still say
nanoseconds).

The first timestamp is always the same, so it's not even an actual
time value, which makes it very difficult to convert these times to
UTC or to compare them with timestamps from other sensors. I also have
no idea whether these values are going to be affected by jumps in the
UTC clock or not. Can anyone explain what is happening here and
whether there is some hope of a stable API in the future?

-Max


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