VolksForth/8086/msdos/tasker.fb

\                                                 ks 22 dez 87  The multitasker is a simple yet powerful round robin scheme     with explicit task switching. This has the major advantage      that the system switches tasks only in known states.            Hence the difficulties in synchronizing tasks and locking       critical portions of code are greatly minimized or simply       do not exist at all.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            \ Multitasker loadscreen                          ks 03 apr 88    Onlyforth   \needs Assembler   2 loadfrom asm.scr                                                                               Code stop         $E990 # U ) mov  ' pause @ # jmp   end-code                                                                   : singletask   [ ' noop @  ] Literal  ['] pause ! ;             : multitask    [ ' pause @ ] Literal  ['] pause ! ;                                                                             1 3 +thru   .( Multitasker geladen) cr                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        \ pass activate                                   ks  1 jun 87                                                                    : pass      ( n0 ... nr-1 Taddr r -- )                        BEGIN [ rot ]                                                       swap $E9CD over !       \ awake Task                            r> -rot                 \ Stack: IP r addr                      8 + >r                  \ s0 of Task                            r@ 2+ @ swap            \ Stack:  IP r0 r                       2+ 2*                   \ bytes on Taskstack incl. r0 & IP      r@ @ over -             \ new SP                                dup r> 2- !             \ into Ssave                            swap bounds  ?DO  I !  2 +LOOP  ;  restrict                                                                                   : activate  ( Taddr -- )  0  \ [ ' pass >body ] Literal >r ;  [ -rot ] REPEAT ; restrict                                                                                                      ( Building a Task                          ks  8 may 84 )                                                                       | : taskerror   ( string -- )   standardi/o  singletask              ." Task error: " count type multitask stop ;                                                                                 : sleep     ( addr -- )    $90 swap c! ;                                                                                        : wake      ( addr -- )    $CD swap c! ;                                                                                        : rendezvous   ( semaphoraddr -- )                                 dup unlock  pause  lock ;