Separate out headers for structures

Makefile

@@ -50,7 +50,7 @@ com/%.com: com/%.asm
 	$(NASM) $(NASM_ARGS) -o $@ $<
 
 bdos/%.bin: bdos/%.asm lib/*.asm
-	$(NASM) $(NASM_ARGS) -o $@ -I bdos $<
+	$(NASM) $(NASM_ARGS) -o $@ $<
 
 bios/%.bin: bios/%.asm
 	$(NASM) $(NASM_ARGS) -o $@ $<

bdos/8086.asm

@@ -1,18 +1,15 @@
 ORG BDOS
 
-%include "bios/header.asm"
+%include "hdr/bios.asm"
+%include "hdr/fcb.asm"
+%include "hdr/bpb.asm"
 
 DISKBUF: EQU (BDOS-0x200) ; deblocking
-STACK:   EQU (DISKBUF) ; grows down
-DEFDRV:  EQU 4
+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
 
-FCB_DRV: EQU 0  ; BYTE 0=A: 1=B: 2=C: ...
-FCB_NAM: EQU 1  ; 8 BYTES, space padded
-FCB_EXT: EQU 9  ; 3 BYTES, space padded
-FCB_TYP: EQU 12 ; 1 for regular file
-FCB_BLK: EQU 13 ; current 128b block in sector
-FCB_CLU: EQU 14 ; current sector
-FCB_LFT: EQU 16 ; bytes left to read in current file
+DEFDRV:  EQU 4 ; default drive when opening a FCB
 
 SYSCALL:
   TEST CL, CL
@@ -25,8 +22,9 @@ SYSCALL:
   JE PUTS
   CMP CL, 10
   JE GETS
-  STC
-  RET
+  CMP CL, 11
+  JE STATUS
+  JMP SYSCALL2
 
 SETUP:
   MOV SP, STACK
@@ -34,16 +32,10 @@ SETUP:
   MOV CX, DISKBUF
   CALL SETDMA
 
-  MOV DL, BYTE [DEFDRV]
-  ADD DL, '@'
-  CALL PUTC
-  MOV DL, '>'
-  CALL PUTC
+  MOV CL, 0x00
+  CALL LOADBPB
 
-  MOV DX, 0x7F
-  MOV BYTE [0x7F], 0x2F
-  MOV BYTE [0x80], 2
-  CALL GETS
+  MOV AX, [DISKBPB]
 
   INT3
 
@@ -63,8 +55,7 @@ GETC:
   ret
 
 PUTC:
-  CALL CONOUT
-  RET
+  JMP CONOUT
 
 PUTS:
   PUSH SI
@@ -134,3 +125,53 @@ GETS_BS:
   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

hdr/bpb.asm

@@ -0,0 +1,12 @@
+; BPB from first sector on FAT fs, starting 0x0B
+BPB_SS:  EQU 0  ; WORD sector size
+BPB_SC:  EQU 2  ; BYTE sectors per cluster
+BPB_RSC: EQU 3  ; WORD reserved sector count
+BPB_FN:  EQU 5  ; BYTE number of FATs
+BPB_RDE: EQU 6  ; WORD number of root directory entries
+BPB_TS:  EQU 8  ; WORD total number of sectors
+BPB_MI:  EQU 10 ; BYTE medium identifier
+BPB_SF:  EQU 11 ; WORD sectors per FAT
+BPB_SPT: EQU 13 ; WORD sectors per track
+BPB_NOS: EQU 15 ; WORD number of sides/heads
+BPB_PO:  EQU 17 ; DWORD partition offset

hdr/fcb.asm

@@ -0,0 +1,10 @@
+; File control block
+FCB_DRV: EQU 0  ; BYTE 0=A: 1=B: 2=C: ...
+FCB_NAM: EQU 1  ; 8 BYTES, space padded
+FCB_EXT: EQU 9  ; 3 BYTES, space padded
+FCB_TYP: EQU 12 ; BYTE FCB type
+; TYP=1: regular file
+FCB_BLK: EQU 13 ; current 128b block in sector
+FCB_CLU: EQU 14 ; current sector
+FCB_LFT: EQU 16 ; bytes left to read in current file
+FCB_END: EQU 20 ; FCB length