find root directory for fcb opening

bdos/8086.asm

@@ -6,10 +6,10 @@ ORG BDOS
 
 DISKBUF: EQU (BDOS-0x200) ; deblocking
 DISKBPB: EQU (DISKBUF-21) ; BPB of the current driv
-DISKDRV: EQU (DISKBPB-1) ; BYTE denoting drive of current fcb
+DISKDRV: EQU (DISKBPB-1) ; BYTE denoting drive of current fcb (1=A, ...)
 STACK:   EQU (DISKDRV & 0xFFFE) ; even address, grows down
 
-DEFDRV:  EQU 4 ; default drive when opening a FCB
+DEFDRV:  EQU 4 ; default drive when opening a FCB (1=A, ...)
 
 SYSCALL:
   TEST CL, CL
@@ -32,12 +32,9 @@ SETUP:
   MOV CX, DISKBUF
   CALL SETDMA
 
-  MOV CL, 0x00
-  CALL LOADBPB
-
-  MOV AX, [DISKBPB]
-
-  INT3
+  SUB SP, 0x20
+  MOV BX, SP
+  CALL FCBOPEN
 
   CLI
 HALT:
@@ -135,6 +132,8 @@ SYSCALL2:
   CMP CL, 14
   JE SETDEFDSK
   CMP CL, 15
+  JE FCBOPEN
+RET:
   RET
 
 DISKRST:
@@ -145,9 +144,63 @@ SETDEFDSK:
   MOV BYTE [DEFDRV], DL
   RET
 
-; IN CL drive num
-LOADBPB:
+FCBOPEN:
+  MOV CL, BYTE [BX]
+  TEST CL, CL
+  JNZ NODEFDRV
+  MOV CL, BYTE [DEFDRV]
+  MOV BYTE [BX], CL
+NODEFDRV:
+  CALL LOADBPB
+
+  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
+
+; 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
@@ -158,8 +211,13 @@ LOADBPB:
   ; 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
@@ -168,10 +226,8 @@ LOADBPB:
   REP MOVSB
   POP DI
   POP SI
-  ; store drive number
   POP CX
+
+  ; store drive number
   MOV BYTE [DISKDRV], CL
   RET
-
-FCBOPEN:
-  RET