ORG BDOS

%include "hdr/bios.asm"
%include "hdr/fcb.asm"
%include "hdr/bpb.asm"

DISKBUF: EQU (BDOS-0x200) ; deblocking
DISKBPB: EQU (DISKBUF-21) ; BPB of the current driv
DISKDRV: EQU (DISKBPB-1) ; BYTE denoting drive of current fcb
STACK:   EQU (DISKDRV & 0xFFFE) ; even address, grows down

DEFDRV:  EQU 4 ; default drive when opening a FCB

SYSCALL:
  TEST CL, CL
  JE SETUP
  CMP CL, 1
  JE GETC
  CMP CL, 2
  JE PUTC
  CMP CL, 9
  JE PUTS
  CMP CL, 10
  JE GETS
  CMP CL, 11
  JE STATUS
  JMP SYSCALL2

SETUP:
  MOV SP, STACK
  MOV BYTE [DEFDRV], 0x01
  MOV CX, DISKBUF
  CALL SETDMA

  MOV CL, 0x00
  CALL LOADBPB

  MOV AX, [DISKBPB]

  INT3

  CLI
HALT:
  HLT
  JMP HALT

GETC:
  CALL CONIN
  TEST AL, AL
  JZ GETC
  PUSH DX
  MOV DL, AL
  CALL CONOUT
  POP DX
  ret

PUTC:
  JMP CONOUT

PUTS:
  PUSH SI
  MOV SI, DX
PUTS_L:
  MOV DL, BYTE [SI]
  CMP DL, '$'
  JZ PUTS_E
  CALL CONOUT
  INC SI
  JMP PUTS_L
PUTS_E:
  POP SI
  RET

; BX base ptr to buffer
; CH maximum BL
; CL minimum BL
GETS:
  PUSH AX
  PUSH CX
  PUSH DX
  PUSH BX
  ; BX is base pointer
  MOV BX, DX
  ; CL is maximum, CH is current position
  MOV CX, [BX]
  XOR CH, CH
  ; BX starts at actual character area
  ADD BX, 2
GETS_L:
  ; Read and maybe handle control chars
  CALL GETC
  CMP AL, 0x0D
  JE GETS_E
  CMP AL, 8
  JE GETS_BS
  ; Store character
  PUSH BX
  ADD BL, CH
  ADC BH, 0
  MOV [BX], AL
  POP BX
  ; Loop if we arent full yet
  INC CH
  CMP CH, CL
  JC GETS_L
GETS_E:
  ; Append LF to CR
  MOV DL, 0x0A
  CALL PUTC
  ; Write back length data
  SUB BX, 2
  MOV [BX], CX
  ; Restore registers
  POP BX
  POP DX
  POP CX
  POP AX
  ret
GETS_BS:
  TEST CH, CH
  JZ GETS_L
  MOV DL, 0x20
  CALL PUTC
  MOV DL, 8
  CALL PUTC
  DEC CL
  JMP GETS_L

STATUS:
  JMP CONST

SYSCALL2:
  CMP CL, 13
  JE DISKRST
  CMP CL, 14
  JE SETDEFDSK
  CMP CL, 15
  RET

DISKRST:
  MOV BYTE [DISKDRV], 0xFF
  RET

SETDEFDSK:
  MOV BYTE [DEFDRV], DL
  RET

; IN CL drive num
LOADBPB:
  PUSH CX
  CALL SELDSK
  ; first track
  MOV CX, 0
  CALL SETTRK
  ; first sector
  MOV CX, 1
  CALL SETSEC
  ; into default diskbuf
  MOV CX, DISKBUF
  CALL SETDMA
  CALL READ
  ; copy BPB
  PUSH SI
  PUSH DI
  MOV CX, 21
  MOV SI, DISKBUF+0x0B
  MOV DI, DISKBPB
  REP MOVSB
  POP DI
  POP SI
  ; store drive number
  POP CX
  MOV BYTE [DISKDRV], CL
  RET

FCBOPEN:
  RET