;=========== BEGIN kbsvc =============
;-- kbsvc.asm
;-- Keyboard service.
;--    getc: get one char of kb input in R0.
;--    kb_int: handle keyboard interrupts.
;--    kb_init: Set up IVT slot, turn on interrupts.
;-------------------------------------
;-------------------------------------

  ;;;------------------------------------------------
  ;;;-- getc
  ;;;-- Get the next char from the keyboard buffer.
  ;;;-- Returns it in R0. If none is available, waits.
  ;;;-- Simple waiting: loop until ready.
  ;;;-- Real waiting: return to OS, which suspends current
  ;;;-- process and does other work. Interrupt handler, kb_int 
  ;;;-- will 
  ;--------------------------------------------------

  getc_BEGIN: ;--------------------------------------
    push__( r1 )          ;-- save reg
    pop__( r1 )           ;-- unsave reg
  getc_END: ret ;------------------------------------

  ;;;------------------------------------------------
  ;;;-- kb_int
  ;;;-- Get char from keyboard, store in buffer.
  ;--------------------------------------------------
  kb_int_BEGIN: ;--------------------------------------
    push__( r0 )          ;-- save reg
    ldi r0, KBDR          ;-- get char
    st r0, kb_buf         ;-- put it in buffer.
    pop__( r0 )           ;-- unsave reg
  kb_int_END: rti ;-------------------------------

  ;;;------------------------------------------------
  ;;;-- kb_init
  ;;;--     Sets IVT slot at x0180 to kb_int_BEGIN.
  ;--------------------------------------------------
  kb_init_BEGIN: ;---------------------------------
    push__( r0 )          ;-- save reg
    push__( r1 )          ;-- save reg
    ld  r0, KB_IVT_LOC    ;-- r0 <== vector slot addr
    lea r1, kb_int_BEGIN  ;-- r1 <== svc routine addr
    str r1, r0,  0        ;-- IVT[r0] <== routine addr
    pop__( r1 )           ;-- unsave reg
    pop__( r0 )           ;-- unsave reg
  kb_init_END: ret ;-------------------------------

  ;;;------------------------------------------------
  ;;;-- KB Data area
  ;--------------------------------------------------
  KB_IVT_LOC:   .FILL x0180   ;-- kb IVT slot.
  GETC_IVT_LOC: .FILL x0020   ;-- getc TVT slot.
  KBSR:         .FILL xFE00   ;-- address of KBSR.
  KBDR:         .FILL xFE02   ;-- address of KBDR.
  kb_ENmask:    .FILL x4000   ;-- ENmask[14] = 1
  kb_buf:       .STRINGZ "*"  ;-- one-char buffer.

;=========== END kbsvc =============