SECTION "Operations", ROM0

; For all instructions, b contains the current op stage

; [in] a: instruction
; [in] b: stage index
; 0b0000
op_hlt:
  ld c, a
  ld a, b

  cp 2
  jr nz, .exit

.stage_2:
  ld hl, ctrl
  set CTRL_HT, [hl]

.exit:
  ld c, a
  ret

; 0b0001
op_lda:
  ld c, a
  ld a, b

  cp 2
  jr z, .stage_2
  cp 3
  jr z, .stage_3
  jr .exit

.stage_2:
  ld hl, ctrl
  set CTRL_MI, [hl]
  set CTRL_IO, [hl]
  jr .exit

.stage_3:
  ld hl, ctrl
  set CTRL_RO, [hl]
  set CTRL_AI, [hl]

.exit:
  ld c, a
  ret

; 0b0010
op_add:
  ld c, a
  ld a, b

  cp 2
  jr z, .stage_2
  cp 3
  jr z, .stage_3
  cp 4
  jr z, .stage_4
  jr .exit

.stage_2:
  ld hl, ctrl
  set CTRL_MI, [hl]
  set CTRL_IO, [hl]
  jr .exit

.stage_3:
  ld hl, ctrl
  set CTRL_RO, [hl]
  inc hl
  set CTRL_BI, [hl]
  jr .exit

.stage_4:
  ld hl, ctrl
  set CTRL_AI, [hl]
  inc hl
  set CTRL_EO, [hl]
  set CTRL_FI, [hl]

.exit:
  ld c, a
  ret

; 0b0011
op_sub:
  ld c, a
  ld a, b
  cp 2
  jr z, .stage_2
  cp 3
  jr z, .stage_3
  cp 4
  jr z, .stage_4
  jr .exit

.stage_2:
  ld hl, ctrl
  set CTRL_MI, [hl]
  set CTRL_IO, [hl]
  jr .exit

.stage_3:
  ld hl, ctrl
  set CTRL_RO, [hl]
  inc hl
  set CTRL_BI, [hl]
  jr .exit

.stage_4:
  ld hl, ctrl
  set CTRL_AI, [hl]
  inc hl
  set CTRL_EO, [hl]
  set CTRL_SU, [hl]
  set CTRL_FI, [hl]

.exit:
  ld c, a
  ret

; 0b0100
op_sta:
  ld c, a
  ld a, b

  cp 2
  jr z, .stage_2
  cp 3
  jr z, .stage_3
  jr .exit

.stage_2:
  ld hl, ctrl
  set CTRL_MI, [hl]
  set CTRL_IO, [hl]
  jr .exit

.stage_3:
  ld hl, ctrl
  set CTRL_AO, [hl]
  set CTRL_RI, [hl]

.exit:
  ld c, a
  ret

; 0b0101
op_ldi:
  ld c, a
  ld a, b

  cp 2
  jr nz, .exit

.stage_2:
  ld hl, ctrl
  set CTRL_IO, [hl]
  set CTRL_AI, [hl]

.exit:
  ld c, a
  ret

; 0b0110
op_jmp:
  ld c, a
  ld a, b

  cp 2
  jr nz, .exit

.stage_2:
  ld hl, ctrl
  set CTRL_IO, [hl]
  inc hl
  set CTRL_JP, [hl]

.exit:
  ld c, a
  ret

; [in] a: instruction
; [in] b: stage index
; 0b0111
op_jc:
  ld c, a ; save instruction
  ld a, b

  cp 2
  jr nz, .exit

.stage_2:
  ; save stage index
  ld d, a

  ld hl, ctrl
  set CTRL_IO, [hl]
  inc hl

  ld a, [flags]
  bit FLAG_C, a
  jr z, .exit
  set CTRL_JP, [hl]

.exit:
  ; restore stage index
  ld a, d
  ld c, a
  ret

; [in] a: instruction
; [in] b: stage index
; 0b1000
op_jz:
  ld c, a ; save instruction
  ld a, b

  cp 2
  jr nz, .exit

.stage_2:
  ; save stage index
  ld d, a

  ld hl, ctrl
  set CTRL_IO, [hl]
  inc hl

  ld a, [flags]
  bit FLAG_Z, a
  jr z, .exit
  set CTRL_JP, [hl]

.exit:
  ; restore stage index
  ld a, d
  ld c, a
  ret

; 0b1111
op_out:
  ld c, a
  ld a, b

  cp 2
  jr nz, .exit

.stage_2:
  ld hl, ctrl
  set CTRL_AO, [hl]
  inc hl
  set CTRL_OI, [hl]

.exit:
  ld c, a
  ret