27.1 Introduction to timecalls.c
As you may already know, in a real time application (as a game), you need to control in-game time evolution.
For example, you cannot increment a car position by 1 at each frame since it will generate an irregular scrolling (a frame is never rendered within the same time as the previous or the next one).
Raydium supports timecalls, wich are a great solution for this problem. Usage is very simple: write a simple function, and ask Raydium to call it at the desired rate.
There is an important risk with timecalls: infinite loops.
If a callback is long, it may take more CPU time than he would, as in this very simple example:
foo() is a function, taking 200 ms for his own execution. If you ask for a 6 Hz execution, Raydium will execute foo() six times on the first frame, taking 1200 ms. On the next frame, Raydium will need to execute foo() 7 times (the asked 6 times, and one more for the 200 ms lost during the last frame), taking 1400 ms, so 8 times will be needed for the next frame, then 9, ...
So you need to create callbacks as short as possible, since long callbacks may cause a game freeze on slower machines than yours. (1 FPS syndrom)
27.1.3 Hardware devices and methods
Raydium must use a very accurate system timer, and will try many methods:
/dev/rtc , gettimeofday() (linux only) and GetTickCount?
?() for win32.
gettimeofday() will use a CPU counter and is extremely accurate. It's far the best method. (0.001 ms accuracy is possible)
/dev/rtc is quite good, and Raydium will try to configure RTC at RAYDIUM_TIMECALL_FREQ_PREFERED rate (8192 Hz by default), but may require a "/proc/sys/dev/rtc/max-user-freq" modification:
echo 8192 > /proc/sys/dev/rtc/max-user-freq
?() is (for now) the only timer available for windows, allowing a 100 Hz timer in most cases.
You may want to look at index.c for interesting defines about timecalls.
Return to RaydiumApiReference