rom/exec/enable.c

   1 /*
   2     Copyright © 1995-2001, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Enable() - Allow interrupts to occur after Disable().
   6     Lang: english
   7 */
   8 #include <exec/types.h>
   9 #include <exec/execbase.h>
  10 #include <aros/libcall.h>
  11 #include <aros/atomic.h>
  12
  13 /*****************************************************************************/
  14 #undef  Exec
  15 #ifdef UseExecstubs
  16 #    define Exec _Exec
  17 #endif
  18
  19 /*  NAME */
  20 #include <proto/exec.h>
  21
  22         AROS_LH0(void, Enable,
  23
  24 /*  LOCATION */
  25         struct ExecBase *, SysBase, 21, Exec)
  26
  27 /*  FUNCTION
  28         This function will allow interrupts to occur after they have
  29         been disabled by Disable().
  30
  31         Note that calls to Disable() nest, and for every call to
  32         Disable() you need a matching call to Enable().
  33
  34         ***** WARNING *****
  35
  36         Using this function is considered very harmful, and it is
  37         not recommended to use this function for ** ANY ** reason.
  38
  39         It is quite possible to either crash the system, or to prevent
  40         normal activities (disk/port i/o) from occuring.
  41
  42         Note: As taskswitching is driven by the interrupts subsystem,
  43               this function has the side effect of disabling
  44               multitasking.
  45
  46     INPUTS
  47         None.
  48
  49     RESULT
  50         Interrupts will be enabled again when this call returns.
  51
  52     NOTES
  53         This function preserves all registers.
  54
  55         To prevent deadlocks calling Wait() in disabled state breaks
  56         the disable - thus interrupts may happen again.
  57
  58     EXAMPLE
  59         No you DEFINITATELY don't want to use this function.
  60
  61     BUGS
  62         The only architecture that you can rely on the registers being
  63         saved is on the Motorola mc68000 family.
  64
  65     SEE ALSO
  66         Forbid(), Permit(), Disable(), Wait()
  67
  68     INTERNALS
  69         This function must be replaced in the $(KERNEL) or $(ARCH)
  70         directories in order to do some work.
  71
  72 ******************************************************************************/
  73 {
  74 #undef Exec
  75
  76     AROS_LIBFUNC_INIT
  77
  78     /* Only disable interrupts if they are not already disabled. The
  79        initial (enabled) value of IDNestCnt is -1
  80     */
  81
  82     AROS_ATOMIC_DEC(SysBase->IDNestCnt);
  83
  84     if( SysBase->IDNestCnt < 0)
  85     {
  86         /*
  87             We have to enable interrupts, however some silly person
  88             hasn't written the code required to do it yet. They should
  89             have created a file in config/$(KERNEL)/exec or
  90             config/$(ARCH)/exec called disable.c or disable.s which
  91             implements this function.
  92         */
  93
  94 #ifndef __CXREF__
  95 #error You have not written the $(KERNEL) interrupt subsystem!
  96 #endif
  97     }
  98
  99     AROS_LIBFUNC_EXIT
 100 } /* Enable() */