OC-KittenOS/repository/docs/kn-sched

This is an overview of what a program
 can expect from the scheduler.

The kernel's scheduling is entirely,
 and I mean entirely, timer-based.

Everything in the kernel,
 that has to occur the next time the
 CPU has reached the main loop,
 is, without exception, a timer,
 apart from the timer system itself.

That last note is important, since as
 the timer system controls sleeping,
 it must use computer.pullSignal -
 thus, that part of the mechanism is
 not in itself a timer - it is the
 mechanism that waits for timers.

Signals that have been retrieved with
 computer.pullSignal, however, do
 become timers.

Timers are kept in a list, and have
 their "target uptime" - the
 computer.uptime() at which they are
 due to be executed, their callback,
 and after the callback, a list of
 arguments to give to the callback.

The current time as KittenOS NEO
 sees it is available as os.uptime().
 (and the address, as os.address() -
 bit of a cheat, but who's counting?)

This source is always in seconds, and
 so KittenOS NEO timing is always in
 seconds.

The scheduling loop's precise details
 are in the kernel itself, and any
 precise description would be a
 translation into pseudocode of what
 is already there.

But it suffices to note that the
 scheduling loop works by, 16 times
 at most, executing and removing all
 timers from first defined to last
 that have passed their time,
 and getting the minimum time of all
 unexecuted timers during each loop.

The last minimum time, if it exists,
 is then bounded to at least 0.05,
 an OC minimum value for a yield.

The pullSignal is then called with
 the bounded time, if any.

(If no bounded time exists, then the
 system goes into more or less a deep
 freeze, which is useful to conserve
 energy, even when apps are "running"
 but aren't using timers.)

If there is any signal, distEvent is
 called to distribute it to those
 processes with the right accessses,
 with an "h." prefix.

-- This is released into
 the public domain.
-- No warranty is provided,
 implied or otherwise.