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(* Premptive.mod provides the Processes module with a premptive scheduler.
Copyright (C) 2020-2023 Free Software Foundation, Inc.
Contributed by Gaius Mulley <gaius.mulley@southwales.ac.uk>.
This file is part of GNU Modula-2.
GNU Modula-2 is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.
GNU Modula-2 is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.
You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
<http://www.gnu.org/licenses/>. *)
IMPLEMENTATION MODULE Preemptive ;
FROM COROUTINES IMPORT TurnInterrupts, PROTECTION ;
FROM Processes IMPORT Wait, Attach, Detach, Create, ProcessId, Urgency, Activate, SuspendMe ;
FROM RTint IMPORT InitTimeVector, ReArmTimeVector, IncludeVector, ExcludeVector ;
FROM libc IMPORT printf ;
CONST
debugging = FALSE ;
(* The space we request becomes part of a stack request, which generally
has constraints on size and alignment. *)
extraWorkSpace = 10 * 1024 * 1024 ;
(*
timer - the timer process which runs at maximum scheduling priority with
interrupts off. It sleeps for a time quantum, performs a Wait
which will rotate the ready queue and then Waits again.
*)
PROCEDURE timer ;
VAR
vec,
currentUsec,
currentSec : CARDINAL ;
old : PROTECTION ;
BEGIN
IF debugging
THEN
printf ("timer\n");
END ;
old := TurnInterrupts (MAX (PROTECTION)) ;
vec := InitTimeVector (timeSliceUsec, timeSliceSec, MAX (PROTECTION)) ;
IF debugging
THEN
printf ("attach\n");
END ;
Attach (vec) ; (* attach vector to this process. *)
IF debugging
THEN
printf ("include vec\n");
END ;
IncludeVector (vec) ;
LOOP
currentSec := timeSliceSec ;
currentUsec := timeSliceUsec ;
IF debugging
THEN
printf ("timer process about to Wait\n");
END ;
Wait ;
(*
printf ("yes 2 seconds elapsed, suspending\n");
SuspendMe ;
*)
IF debugging
THEN
printf ("timer process wakes up, now calling ReArmTimeVector\n");
END ;
ReArmTimeVector (vec, timeSliceUsec, timeSliceSec) ;
IF debugging
THEN
printf ("ReArmTimeVector complete\n");
printf ("attach\n");
END ;
Attach (vec) ; (* attach vector to this process. *)
IF debugging
THEN
printf ("finished attach, now include vec\n");
END ;
IncludeVector (vec) ;
END
END timer ;
(*
initPreemptive - if millisecs > 0 then turn on preemptive scheduling.
if millisecs = 0 then preemptive scheduling is turned off.
*)
PROCEDURE initPreemptive (seconds, microsecs: CARDINAL) ;
BEGIN
timeSliceUsec := microsecs ;
timeSliceSec := seconds ;
IF NOT init
THEN
init := TRUE ;
Create (timer, extraWorkSpace, MAX (Urgency), NIL, timerId) ;
Activate (timerId)
END
END initPreemptive ;
VAR
init : BOOLEAN ;
timerId : ProcessId ;
timeSliceSec,
timeSliceUsec: CARDINAL ;
BEGIN
init := FALSE ;
timeSliceSec := 0 ;
timeSliceUsec := 0
END Preemptive.
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