Sytem clock skew

[coltonmercurio]

There is a significant difference between files access/modified time and the system time.

This causes issues with programs that compare the system time with file modification time (make).

This has been fixed by changing the following:

• First to resolve the largest difference in time. The AppendDateHack now uses UTC time, making this consistent with the time zone inodes use.
• Changing when the AppendDateHack function is called and what file it appends the date to. It was moved from when the inodes are created/loaded to when the inodes are opened. This was done because after the time correction from the first issue there was still an approx. 6 second difference between the system clock and files. This is because AppendDateHack appends the current date to rcS 6 seconds before it is executed (after boot). So with the new solution (still a hack) the time is appended to '.profile' right before it is executed -- creating the smallest clock skew.

[s-macke]

Thanks for the patch. Yes, there is indeed some discrepancy between the system time and filesystem time. But not only on the hour scale, but also on the second scale, because the system time (emulated) ) can be different from the filesystem time (Javascript function). I don't think, that I can perfectly synchronize them.

[benjamincburns]

Has been a while since I've looked over the codebase or at how the kernel handles fetching timestamps, but perhaps date/time skew in at least CLOCK_REALTIME could be fixed more generically w/ a realtime clock peripheral and a few kernel tweaks?

[s-macke]

Linux syncs its clock exactly one time at boot time with a hardware real time clock. Then it relies fully on the normal timers and calculates the real time itself. I check every 10-20 times a second the Javaxcript realtime (only ms accuray) with the timers and recalculate the "clock cycle per instruction" counter. If it too far off (I think half a second) I reset my counters. Then Javascript and the emulation is out of sync. This happens not so often. With this synchronization trick I also get real time micro second accuracy for the sound emulation.