rom/exec/dispatch.c

   1 /*
   2     Copyright © 1995-2001, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Dispatch() - Tell the system that we have switched tasks.
   6     Lang: english
   7 */
   8
   9 #include <exec/types.h>
  10 #include <exec/lists.h>
  11 #include <exec/tasks.h>
  12 #include <exec/execbase.h>
  13 #include <exec/alerts.h>
  14
  15 #include <proto/arossupport.h>
  16 #include <aros/asmcall.h>
  17
  18 /*****i***********************************************************************
  19
  20     NAME */
  21 #include <proto/exec.h>
  22
  23         AROS_LH0(void, Dispatch,
  24
  25 /*  LOCATION */
  26         struct ExecBase *, SysBase, 10, Exec)
  27
  28 /*  FUNCTION
  29         Inform SysBase that the task has been switched. This function
  30         only does all the non-system-dependant dispatching. It is up
  31         to the implementation to ensure that the tasks do actually get
  32         switched.
  33
  34         The tc_Switch and tc_Launch functions will be called with
  35         SysBase in register A6.
  36
  37     INPUTS
  38         None.
  39
  40     RESULT
  41         The current task will have changed.
  42
  43     NOTES
  44
  45     EXAMPLE
  46
  47     BUGS
  48         Not a good function to call.
  49
  50     SEE ALSO
  51         Switch(), Reschedule()
  52
  53     INTERNALS
  54         You can use your CPU dependant function as a wrapper around this
  55         function if you want. But you have to make sure then that you
  56         do NOT call Dispatch() from the exec.library function table.
  57
  58 ******************************************************************************/
  59 {
  60     AROS_LIBFUNC_INIT
  61
  62     struct Task *this, *task;
  63
  64     this = SysBase->ThisTask;
  65
  66     /* Check the stack... */
  67
  68     /* Get the task which is ready to run */
  69     if(( task = (struct Task *)RemHead(&SysBase->TaskReady)))
  70     {
  71         if(this->tc_Flags & TF_SWITCH)
  72         {
  73             AROS_UFC1(void, this->tc_Switch,
  74             AROS_UFCA(struct ExecBase *, SysBase, A6));
  75         }
  76
  77         this->tc_TDNestCnt = SysBase->TDNestCnt;
  78         this->tc_IDNestCnt = SysBase->IDNestCnt;
  79
  80         /*  Oh dear, the previous task has just vanished...
  81             you should have called Switch() instead :-)
  82
  83             We don't change the state of the old task, otherwise it
  84             may never get freed.(See RemTask() for details).
  85
  86             We especially don't add it to the ReadyList !
  87         */
  88         task->tc_State = TS_RUN;
  89
  90         SysBase->TDNestCnt = task->tc_TDNestCnt;
  91         SysBase->IDNestCnt = task->tc_IDNestCnt;
  92
  93         SysBase->ThisTask = task;
  94
  95         /* Check the stack of the task we are about to launch */
  96
  97         if( task->tc_SPReg <= task->tc_SPLower
  98             || task->tc_SPReg >= task->tc_SPUpper )
  99         {
 100             /* POW! */
 101             Alert(AT_DeadEnd|AN_StackProbe);
 102         }
 103
 104         if(task->tc_Flags & TF_LAUNCH)
 105         {
 106             AROS_UFC1(void, task->tc_Launch,
 107             AROS_UFCA(struct ExecBase *, SysBase, A6));
 108         }
 109
 110         /* Increase the dispatched counter */
 111         SysBase->DispCount++;
 112     }
 113     else
 114     {
 115         kprintf("Eh? No tasks left to Dispatch()\n");
 116
 117     /*
 118         We have reached a point where there are no ready tasks.
 119         What can you do? Well you can basically go into some kind of
 120         loop that can be interrupted easily. If you do this however
 121         you must re-enable interrupts.
 122
 123         If you seem to go into endless loops with nothing happening,
 124         it could be that you have not enabled interrupts, or alternatively
 125         you could be running under emulation, disabled all signals and be
 126         getting some kind of process error (SIGBUS, SIGSEGV etc), which
 127         can't be delivered.
 128
 129         If you do go idle, increase the counter please.
 130
 131         You could also create a task (the idle task), which basically
 132         does nothing, and switch to that, in which case you should never
 133         get to here.
 134
 135                 SysBase->IdleCount++;
 136     */
 137     }
 138
 139     /* Aha, the task pointed to be SysBase->ThisTask is correct. */
 140
 141     AROS_LIBFUNC_EXIT
 142 } /* Dispatch() */