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 (1=A, ...)

PROGBX:  EQU (DISKDRV-2)

STACK:   EQU (PROGBX & 0xFFFE) ; even address, grows down

DEFDRV:  EQU 4 ; default drive when opening a FCB (1=A, ...)

SYSCALL:
  MOV [PROGBX], BX
  XOR BH, BH
  MOV BL, CL
  ADD BX, BX
  ADD BX, FUNCS
  MOV BX, [BX]
  PUSH BX
  MOV BX, [PROGBX]
SYSRET:
  RET

FUNCS:
DW SETUP,GETC,PUTC,SYSRET
DW SYSRET,SYSRET,SYSRET,SYSRET
DW SYSRET,PUTS,GETS,STATUS
DW SYSRET,DISKRST,SETDEFDSK,FCBOPEN
DW SYSRET,SYSRET,SYSRET,SYSRET
DW SYSRET,SYSRET,SYSRET,SYSRET

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

  SUB SP, 0x20
  MOV BX, SP
  CALL FCBOPEN

  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

DISKRST:
  MOV BYTE [DISKDRV], 0xFF
  RET

SETDEFDSK:
  MOV BYTE [DEFDRV], DL
  RET

FCBOPEN:
  MOV CL, BYTE [BX]
  TEST CL, CL
  JNZ NODEFDRV
  MOV CL, BYTE [DEFDRV]
  MOV BYTE [BX], CL
NODEFDRV:
  CALL LOADBPB

  MOV CX, [DISKBPB+BPB_RDE]

  CALL FATSIZE
  ADD DX, WORD [DISKBPB+BPB_RSC]
  CALL SETLSEC
  CALL READ

  MOV AX, [DISKBUF]

  INT3
  ; TODO: search for file in rootdir
  ; TODO: init cluster number
  RET

; Set logical sector number
; IN DX sector number
SETLSEC:
  PUSH AX
  PUSH CX
  PUSH DX
  XOR AX, AX
  XCHG AX, DX
  DIV WORD [DISKBPB+BPB_SPT]
  MOV CX, AX
  CALL SETTRK
  MOV CX, DX
  INC CX
  CALL SETSEC
  POP DX
  POP CX
  POP AX
  RET

; OUT DX number of sectors by all FATs
FATSIZE:
  PUSH AX
  MOV DL, BYTE [DISKBPB+BPB_FN]
  MOV AL, BYTE [DISKBPB+BPB_SF]
  MUL DL
  XCHG AX, DX
  POP AX
RET:
  RET

; IN CL drive num, 1=A, 2=B, 3=C
LOADBPB:
  CMP BYTE [DISKDRV], CL
  JE RET

  PUSH CX
  DEC CL
  CALL SELDSK
  ; first track
  MOV CX, 0
  CALL SETTRK
  ; first sector
  MOV CX, 1
  CALL SETSEC
  ; into default diskbuf
  MOV CX, DISKBUF
  CALL SETDMA
  POP CX

  CALL READ
  JC DISKRST

  ; copy BPB
  PUSH CX
  PUSH SI
  PUSH DI
  MOV CX, 21
  MOV SI, DISKBUF+0x0B
  MOV DI, DISKBPB
  REP MOVSB
  POP DI
  POP SI
  POP CX

  ; store drive number
  MOV BYTE [DISKDRV], CL
  RET