{ 0x100 var, userhere
  : userallot userhere @ + userhere ! ;
  : userarray userhere @ CONST userallot ;
  : uservar cell userarray ; }

uservar tasksp 
uservar taskbp
uservar tasksi
uservar taskcoff
uservar taskcs
uservar next-task

:asm @u ( p -- v )
  POP BX
  PUSH @[ SS: BX]
  NEXT

:asm !u ( v p -- )
  POP BX
  POP AX
  MOV @[ SS: BX] AX
  NEXT

:asm get-cseg PUSH CS NEXT
{ :asm get-host-cseg PUSH CS NEXT }

:asm suspend
  MOV @[ SS: taskcs @] CS
  MOV @[ SS: tasksp @] SP
  MOV @[ SS: taskbp @] BP
  MOV @[ SS: tasksi @] SI
  MOV AX @[ SS: next-task @]
L: resume-task-ax
  MOV SS AX
  MOV SP @[ SS: tasksp @]
  MOV BP @[ SS: taskbp @]
  MOV SI @[ SS: tasksi @]
  MOV DS @[ SS: taskcs @]
  LODSW
  MOV BX AX
  MOV AX @[ BX]
  MOV @[ SS: taskcoff @] AX
  JMP FAR @[ SS: taskcoff @]

:asm resume-task ( taskseg -- )
  POP AX
  JMP resume-task-ax

:asm taskseg
  PUSH SS
  NEXT

0 var, first-task
0 var, last-task
0x200 4 >> const tasksegsize

( taskseg -- taskseg )
deferred task-init noop

: init-first-task 
  taskseg dup next-task !u task-init dup first-task ! last-task ! ;

init-first-task
' init :chain init-first-task ;

:asm unlink-task ( prevtaskseg taskseg -- )
  MOV CX SS
  POP AX
  POP BX
  MOV SS AX
  MOV DX @[ SS: next-task @]
  XOR AX AX
  MOV @[ SS: next-task @] AX
  MOV SS BX
  MOV @[ SS: next-task @] DX
  MOV SS CX
  NEXT

: prev-taskseg ( -- taskseg )
  first-task @ begin next-task over @far taskseg != while 
                     tasksegsize + repeat ;
: next-unused-taskseg
  first-task @ begin next-task over @far over last-task @ <= and while 
                     tasksegsize + repeat ;

: task-complete next-task @u prev-taskseg taskseg unlink-task resume-task [
: task-arise execute task-complete [
{ : task-arise-host execute task-complete [ }

:asm link-new-task ( taskseg -- )
  MOV CX SS
  POP AX ( taskseg )
  ( save the current next task in BX so we can point the new task at it )
  MOV BX @[ SS: next-task @]
  ( link our task segment to the new task )
  MOV @[ SS: next-task @] AX
  MOV SS AX
  MOV AX 0x100 # 
  MOV @[ SS: tasksp @]    AX
  XOR AX AX
  MOV @[ SS: taskbp @]    AX
  MOV @[ SS: next-task @] BX
  MOV SS CX ( restore the current task )
  NEXT

: push-into-task ( v taskseg -- ) 
  >r tasksp r@ @far 2 - dup tasksp r@ !far <r !far ;
: spawn-task-raw ( cp cseg arise -- taskseg ) 
  next-unused-taskseg >r r@ link-new-task
  r@ last-task @ > if r@ last-task ! then
  cell + tasksi r@ !far
  taskcs r@ !far
  r@ push-into-task 
  <r task-init ;

: spawn-task ( cp -- taskseg )
  get-cseg ' task-arise spawn-task-raw ;
{ : spawn-task ( cp -- taskseg )
    get-host-cseg ' task-arise-host spawn-task-raw ; }