rom/exec/enable.c

   1 /*
   2     Copyright © 1995-2018, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Enable() - Allow interrupts to occur after Disable().
   6     Lang: english
   7 */
   8
   9 #define DEBUG 0
  10
  11 #include <exec/execbase.h>
  12 #include <aros/libcall.h>
  13 #include <aros/atomic.h>
  14
  15 #include "exec_intern.h"
  16
  17 /*****************************************************************************/
  18 #undef  Exec
  19 #ifdef UseExecstubs
  20 #    define Exec _Exec
  21 #endif
  22
  23 /*  NAME */
  24 #include <proto/exec.h>
  25
  26         AROS_LH0(void, Enable,
  27
  28 /*  LOCATION */
  29         struct ExecBase *, SysBase, 21, Exec)
  30
  31 /*  FUNCTION
  32         This function will allow interrupts to occur (*) after they have
  33         been disabled by Disable().
  34
  35         Note that calls to Disable() nest, and for every call to
  36         Disable() you need a matching call to Enable().
  37
  38         ***** WARNING *****
  39
  40
  41         Using this function is considered very harmful, and it should only
  42         ever be used to protect data that could also be accessed in interrupts.
  43
  44         It is quite possible to either crash the system, or to prevent
  45         normal activities (disk/port i/o) from occuring.
  46
  47     INPUTS
  48         None.
  49
  50     RESULT
  51         Interrupts will be enabled again when this call returns.
  52
  53     NOTES
  54         This function preserves all registers.
  55
  56         To prevent deadlocks calling Wait() in disabled state breaks
  57         the disable - thus interrupts may happen again.
  58
  59         As the schedulers pre-emption is interrupt driven,
  60         this function has the side effect of disabling
  61         multitasking.
  62
  63         (*) On EXECSMP builds, Enable() only applies to the processor
  64             it is called from. Data which needs to be protected from
  65             parallel access will also require a spinlock.
  66
  67     EXAMPLE
  68         In most userspace code, you will not want to use this function.
  69
  70     BUGS
  71         The only architecture that you can rely on the registers being
  72         saved is on the Motorola mc68000 family.
  73
  74     SEE ALSO
  75         Forbid(), Permit(), Disable(), Wait()
  76
  77     INTERNALS
  78
  79 ******************************************************************************/
  80 {
  81 #undef Exec
  82
  83     AROS_LIBFUNC_INIT
  84
  85     D(bug("[Exec] Enable()\n");)
  86
  87     IDNESTCOUNT_DEC;
  88
  89     D(bug("[Exec] Enable: IDNESTCOUNT = %d\n", IDNESTCOUNT_GET);)
  90
  91     if (KernelBase)
  92     {
  93         if (IDNESTCOUNT_GET < 0)
  94         {
  95             D(bug("[Exec] Enable: Enabling interrupts\n");)
  96
  97             /* The following stuff is not safe to call from within supervisor mode */
  98             if (!KrnIsSuper())
  99             {
 100                 KrnSti();
 101
 102                 /*
 103                  * There's no dff09c like thing in x86 native which would allow
 104                  * us to set delayed (mark it as pending but it gets triggered
 105                  * only once interrupts are enabled again) software interrupt,
 106                  * so we check it manually here in Enable(), similar to Permit().
 107                  */
 108                 if (SysBase->SysFlags & SFF_SoftInt)
 109                 {
 110                     /*
 111                      * First we react on SFF_SoftInt by issuing KrnCause() call. This triggers
 112                      * the complete interrupt processing code in kernel, which implies also
 113                      * rescheduling if it becomes necessary.
 114                      */
 115                     D(bug("[Exec] Enable: causing softints\n");)
 116                     KrnCause();
 117                 }
 118
 119                 if ((TDNESTCOUNT_GET < 0) && FLAG_SCHEDSWITCH_ISSET)
 120                 {
 121                     /*
 122                      * If SFF_SoftInt hasn't been set, we have a chance that task switching
 123                      * is enabled and pending. We need to trigger it here in such a case.
 124                      */
 125                     D(bug("[Exec] Enable: rescheduling\n");)
 126                     KrnSchedule();
 127                 }
 128             }
 129         }
 130     }
 131
 132     AROS_LIBFUNC_EXIT
 133 } /* Enable() */