arch/.unmaintained/m68k-native/exec/disable.s

   1 /*
   2     Copyright © 1995-2001, The AROS Development Team. All rights reserved.
   3     $Id$
   4 */
   5
   6 /*****************************************************************************
   7
   8     NAME
   9
  10         AROS_LH0(void, Disable,
  11
  12     LOCATION
  13         struct ExecBase *, SysBase, 20, Exec)
  14
  15     FUNCTION
  16         This function disables the delivery of all interrupts until a matching
  17         call to Enable() is done. This implies a Forbid(). Since the system
  18         needs the regular delivery of all interrupts it is forbidden to disable
  19         them for longer than ~250 microseconds.
  20
  21         THIS CALL IS VERY DANGEROUS!!!
  22
  23         Do not use it without thinking very well about it or better do not use
  24         it at all. Most of the time you can live without it by using semaphores
  25         or similar.
  26
  27         Calls to Disable() nest, i.e. for each call to Disable() you need one
  28         call to Enable().
  29
  30     INPUTS
  31
  32     RESULT
  33
  34     NOTES
  35         This function preserves all registers.
  36
  37         This function may be used from interrupts to disable all higher
  38         priority interrupts. Lower priority interrupts are disabled anyway.
  39
  40         To prevent deadlocks calling Wait() in disabled state breaks the
  41         disable - thus interrupts and taskswitches may happen again.
  42
  43     EXAMPLE
  44
  45     BUGS
  46
  47     SEE ALSO
  48         Forbid(), Permit(), Enable(), Wait()
  49
  50     INTERNALS
  51         For old exec Disable() there exists an assembler macro replacement
  52         that is (of course) unportable. Using a Disable() implementation
  53         equal to this macro would not only have some impact on Disable()
  54         itself but also on other functions (e.g. Signal()).
  55         Therefore I decided to drop support for this macro to a certain
  56         extent. The difference is only minuscule:
  57         If a task uses the assembler macro and activates some higher priority
  58         task he cannot expect this task to be awakened immediately at Enable()
  59         but only at the next context switch. But I do not think that this
  60         poses any problems.
  61
  62     HISTORY
  63
  64 ******************************************************************************/
  65
  66         INTENA      =   0xdff09a
  67         INTEN       =   0x4000
  68         SET         =   0x8000
  69
  70         #include "machine.i"
  71
  72         .text
  73         .balign 4
  74         .globl  AROS_SLIB_ENTRY(Disable,Exec)
  75         .type   AROS_SLIB_ENTRY(Disable,Exec),@function
  76 AROS_SLIB_ENTRY(Disable,Exec):
  77         /* disable interrupts */
  78         move.w  #INTEN,INTENA
  79
  80         /* increment nesting count and return */
  81         addq.b  #1,IDNestCnt(a6)
  82         rts
  83