ORG (RAM-0x600)
CPU 8086

DISKCX: EQU 0x40
DISKDL: EQU 0x42
DISKDH: EQU 0x43
DISKBX: EQU 0x44

JMP NEAR BOOT
JMP NEAR WBOOT
JMP NEAR CONST
JMP NEAR CONIN
JMP NEAR CONOUT
JMP NEAR LIST
JMP NEAR PUNCH
JMP NEAR READER
JMP NEAR HOME
JMP NEAR SELDSK
JMP NEAR SETTRK
JMP NEAR SETSEC
JMP NEAR SETDMA
JMP NEAR READ
JMP NEAR WRITE
JMP NEAR LISTST
JMP NEAR SECTRAN

BOOT:
  STC
  RET

WBOOT:
  STC
  RET

; CHAR I/O
CONST:
  MOV AH, 1
  INT 0x16
  JZ .END
  MOV AL, 0xFF
  RET
.END:
  XOR AL, AL
  RET

CONIN:
  XOR AX, AX
  INT 0x16
  TEST AL, AL
  JZ CONIN
  RET

CONOUT:
  PUSH AX
  PUSH BX
  MOV AH, 0x0E
  MOV AL, DL
  XOR BX, BX
  INT 0x10
  POP BX
  POP AX
  RET

LIST:
  PUSH DX
  XOR AH, AH
  MOV AL, DL
  INT 0x17
  POP DX
  RET

LISTST:
  STC
  RET

PUNCH:
  STC
  RET

READER:
  STC
  RET

; DISK I/O
HOME:
  RET

SELDSK:
  MOV BYTE [DISKDL], CL
  XOR BX, BX
  RET

SETTRK:
  PUSH CX
  PUSH DX

  MOV DX, CX
  ; CH for headnum, CL for SAL
  MOV CX, 0x0006

  ; Take off LSB as head number
  XOR CH, CH
  RCR DX, 1
  RCL CH, 1
  MOV BYTE [DISKDH], CH

  ; DX is sector number now
  ; Shift into format for int13
  ; DX ------9876543210
  SAL DX, CL
  ; DX 9876543210------
  ROL DX, 1
  ROL DX, 1
  ; DX 76543210------98
  SAL DL, CL
  ; DX 7654321098------
  AND WORD [DISKCX], 0x003F
  OR WORD [DISKCX], DX

  POP DX
  POP CX
  RET

SETSEC:
  STC
  RET

SETDMA:
  MOV WORD [DISKBX], CX
  RET

READ:
  STC
  RET

WRITE:
  STC
  RET

SECTRAN:
  STC
  RET