Martin Stein c70fed29f7 os/timer: interpolate time via timestamps ... Previously, the Genode::Timer::curr_time always used the Timer_session::elapsed_ms RPC as back end. Now, Genode::Timer reads this remote time only in a periodic fashion independently from the calls to Genode::Timer::curr_time. If now one calls Genode::Timer::curr_time, the function takes the last read remote time value and adapts it using the timestamp difference since the remote-time read. The conversion factor from timestamps to time is estimated on every remote-time read using the last read remote-time value and the timestamp difference since the last remote time read. This commit also re-works the timeout test. The test now has two stages. In the first stage, it tests fast polling of the Genode::Timer::curr_time. This stage checks the error between locally interpolated and timer-driver time as well as wether the locally interpolated time is monotone and sufficiently homogeneous. In the second stage several periodic and one-shot timeouts are scheduled at once. This stage checks if the timeouts trigger sufficiently precise. This commit adds the new Kernel::time syscall to base-hw. The syscall is solely used by the Genode::Timer on base-hw as substitute for the timestamp. This is because on ARM, the timestamp function uses the ARM performance counter that stops counting when the WFI (wait for interrupt) instruction is active. This instruction, however is used by the base-hw idle contexts that get active when no user thread needs to be scheduled. Thus, the ARM performance counter is not a good choice for time interpolation and we use the kernel internal time instead. With this commit, the timeout library becomes a basic library. That means that it is linked against the LDSO which then provides it to the program it serves. Furthermore, you can't use the timeout library anymore without the LDSO because through the kernel-dependent LDSO make-files we can achieve a kernel-dependent timeout implementation. This commit introduces a structured Duration type that shall successively replace the use of Microseconds, Milliseconds, and integer types for duration values. Open issues: * The timeout test fails on Raspberry PI because of precision errors in the first stage. However, this does not render the framework unusable in general on the RPI but merely is an issue when speaking of microseconds precision. * If we run on ARM with another Kernel than HW the timestamp speed may continuously vary from almost 0 up to CPU speed. The Timer, however, only uses interpolation if the timestamp speed remained stable (12.5% tolerance) for at least 3 observation periods. Currently, one period is 100ms, so its 300ms. As long as this is not the case, Timer_session::elapsed_ms is called instead. Anyway, it might happen that the CPU load was stable for some time so interpolation becomes active and now the timestamp speed drops. In the worst case, we would now have 100ms of slowed down time. The bad thing about it would be, that this also affects the timeout of the period. Thus, it might "freeze" the local time for more than 100ms. On the other hand, if the timestamp speed suddenly raises after some stable time, interpolated time can get too fast. This would shorten the period but nonetheless may result in drifting away into the far future. Now we would have the problem that we can't deliver the real time anymore until it has caught up because the output of Timer::curr_time shall be monotone. So, effectively local time might "freeze" again for more than 100ms. It would be a solution to not use the Trace::timestamp on ARM w/o HW but a function whose return value causes the Timer to never use interpolation because of its stability policy. Fixes #2400		2017-05-31 13:16:11 +02:00
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interface.h	os/timer: interpolate time via timestamps	2017-05-31 13:16:11 +02:00
types.h	Adjust file headers to refer to the AGPLv3	2017-02-28 12:59:29 +01:00