implement fcb search with more efficient segmenting and dta use

com/@rdos.asm

@@ -9,6 +9,7 @@ banner:	db "RDOS KERNEL ", V, 0x0A, 0x0D, '$', 0x1A
 %include "kernel/char.asm"
 %include "inc/bpb.asm"
 %include "kernel/drive.asm"
+%include "kernel/fcb.asm"
 
 section .text
 
@@ -18,20 +19,22 @@ init:	call rstseg
 	mov dx, banner
 	call puts
 
-	mov byte [testbuf], 5
-	mov dx, testbuf
-	call gets
-
-	mov ax, [testbuf]
-	mov cx, [testbuf+2]
-	mov dx, [testbuf+4]
-	mov bx, [testbuf+6]
+	call rstseg
+	mov dx, testdta
+	call setdta
+	mov dx, testfcb
+	call fndfst
 
 	int 3
 
 hlt:	hlt
 	jmp hlt
 
+section .data
+
+testfcb	db 0, "HELLO   ","COM"
+	times FCBSIZ db 0
+
 section .bss
 
-testbuf	resb 130
+testdta	resb 128

kernel/drive.asm

@@ -90,6 +90,7 @@ getprm	test byte [dskflag], 4
 	; copy BIOS dpt table over ours
 	mov dx, dpt
 	mov bx, di
+	mov cx, 11
 	call lodfar
 .ret	ret
 
@@ -112,13 +113,15 @@ logdrv	cmp dl, [dsknum]
 	cmp dl, 2
 	jnc loghdd
 
-	; save info for bios
 logfdd	mov [biosnum], dl
+	; assume some default values
+	xor ax, ax
+	mov word [bpb+BPBHS], ax
+	mov word [bpb+BPBHS+2], ax
+	mov word [bpb+BPBNOS], 2 ; 5 1/4" 360kB
+	mov word [bpb+BPBSPT], 9
 	; reset dpt to defaults
 	call getprm
-	; set default geometry (1.44 MB floppy)
-	mov word [bpb+BPBNOS], 2
-	mov word [bpb+BPBSPT], 18
 	; load boot sector
 	xor ax, ax
 	xor dx, dx
@@ -133,10 +136,6 @@ logfdd	mov [biosnum], dl
 	; copy SPT to DPT
 	mov al, [bpb+BPBSPT]
 	mov [dpt+4], al
-	; make sure partition offset is forced zero
-	xor ax, ax
-	mov [bpb+BPBHS], ax
-	mov [bpb+BPBHS+2], ax
 .ret	ret
 
 loghdd	sub dl, 2
@@ -192,28 +191,13 @@ loghdd	sub dl, 2
 logerr	stc
 	ret
 
-	; counting from begin of cluster area
-mapclu	mov bx, [bpb+BPBRDE]
-	mov cl, 4
-	shr bx, cl ; 32 bytes per entry
-	add ax, bx
-	adc dx, 0
-	; counting from beginning of dir
-	; add fat table sizes
-maprd	xor ch, ch
-	mov cl, byte [bpb+BPBFN]
-.loop	add ax, [bpb+BPBFS]
-	adc dx, 0
-	loop .loop
-	; counting from beginning of FAT
-	; add reserved sector count
-mapfat	add ax, [bpb+BPBRSC]
-	adc dx, 0
 	; count from partition start
-map	add ax, [bpb+BPBHS]
+	; IN	dx:ax	sector number
+maprel	add ax, [bpb+BPBHS]
 	add dx, [bpb+BPBHS+2]
 	; absolute sector count
 	; skip doing a read if sector number matches
+	; IN	dx:ax	sector number
 mapabs	cmp ax, [dskseek]
 	jne read
 	cmp dx, [dskseek+2]

kernel/fcb.asm

@@ -1,94 +1,152 @@
-
 ; FCB layout
 ; 1 byte drive (0=default, 1=A:, 2=B:, ...)
 ; 8.3 filename
 ; 8.3 filename for rename
 
-FCBDEN:	equ 23 ; WORD directory entry number
-FCBSIZ:	equ 30
+FCBSIZ	equ 30
+
+section .data
+
+defdrv	db 0
+dta	dd 0
 
 section .text
 
 	; auto-complete drive field in fcb
-	; also returns the drive number
-	; IN	es:bx	far ptr FCB
-	; OUT	dl	dl (0=A:, 1=B:, 2=C:, ...)
-fcbdrv:	mov dl, [es:bx]
+	; also logs in the drive
+	; IN	ds:dx	far ptr FCB
+fcbdrv	push ds
+	push dx
+	mov si, dx
+	; if currently zero, ...
+	mov dl, [si] ; 1-based
 	test dl, dl
-	jnz .ret
-	call getdd
-	mov dl, al
+	jnz .log
+	; replace with current drive
+	mov dl, [cs:defdrv] ; 0-based
 	inc dl
-	mov [es:bx], dl
-.ret:	dec dl
+	mov [si], dl ; 1-based
+.log	dec dl
+	call logdrv ; 0-based
+	pop dx
+	pop ds
+	; if carry flag set, resume stack at bp
+	; this instant-returns some higher level procs
+	jnc .ret
+	mov sp, bp
+	; duplicate carry bit into all 8 AL bits
+	; similar to SALC instruction
+.ret	sbb al, al
+	ret
+
+	; set disk transfer address
+	; IN	DS:DX	dta ptr
+setdta	mov [cs:dta], dx
+	mov [cs:dta+2], ds
+	ret
+
+	; get disk transfer address
+	; OUT	ES:BX	dta ptr
+getdta	les bx, [cs:dta]
 	ret
 
 	; Load root directory entry
 	; IN	ax	number of directory entry
-	; OUT	cs:si	ptr to directory entry
-lddir:	push ax
+	; OUT	cs:di	ptr to directory entry
+lddir	push ax
+	push ax
+	call rstseg
+	pop ax
 	mov cl, 4
 	shr ax, cl
 	xor dx, dx
-	call maprd
-	; get si to point to entry
-	pop si
+	; dx:ax = sector number in rootdir
+	; add sizes of FAT tables
+	xor ch, ch
+	mov cl, byte [bpb+BPBFN]
+.loop:	add ax, [bpb+BPBFS]
+	adc dx, 0
+	loop .loop
+	; add reserved sector count
+	add ax, [bpb+BPBRSC]
+	adc dx, 0
+	; fetch sector (relative to partition)
+	call maprel
+	; get di to point to entry
+	pop di
 	mov cl, 5
-	shl si, cl
-	and si, 0x1FF
-	add si, dskbuf
+	shl di, cl
+	and di, 0x1FF
+	add di, dskbuf
 	ret
 
 	; find first matching file
-	; IN	ES:BX	input fcb
-fndfst:	; get and log in drive
+	; IN	DS:DX	input fcb
+fndfst	mov bp, sp
 	call fcbdrv
-	call logdrv
 	; set search state to zero
-	push es
-	push bx
-	call getdta
+	les di, [cs:dta]
 	xor ax, ax
-	mov [es:bx+0x20+1], ax
-	pop bx
-	pop es
+	mov [es:di+FCBSIZ], ax
 	; find next matching file
 	; state is kept in DTA
-fndnxt:	; get net direntry to fetch
+fndnxt	mov bp, sp
+	call fcbdrv
+	; get next direntry to fetch
 	; get number of current entry from DTA
-	push es
-	push bx
-	call getdta
-	mov ax, [es:bx+0x20+1]
-	inc word [es:bx+0x20+1]
-	pop bx
-	pop es
+.loop	les di, [cs:dta]
+	mov ax, [es:di+FCBSIZ]
+	inc word [es:di+FCBSIZ]
 	; bail out if we are at end of dir
 	cmp ax, [bpb+BPBRDE]
 	jnc .err
 	; load entry and first byte
-	push bx
+	push ds
+	push dx
 	call lddir
-	pop bx
+	pop dx
+	pop ds
 	; next if hidden, dir or vol label
-	test byte [si+0x0B], 0xDA
-	jnz fndnxt
+	test byte [cs:di+0x0B], 0xDA
+	jnz .loop
 	; bail out if end of dir
-	mov al, [si]
+	mov al, [di]
 	cmp al, 0
 	je .err
 	; next if deleted entry
 	cmp al, 0xE5
-	je fndnxt
-	; compate DS:SI with ES:BX+1
-	lea di, [bx+1]
+	je .loop
+	; DS:SI := FCB+1
+	; ES:DI := CS:dirent
+	mov si, dx
+	push si
+	inc si
+	mov ax, cs
+	mov es, ax
+	; compare and ; try next if mismatch
 	mov cx, 11
+	push di
 	rep cmpsb
-	; try next if mismatch
-	jne fndnxt
-	clc
+	pop di
+	pop si
+	jne .loop
+	; create FCB in DTA
+	call getdta
+	xchg bx, di
+	; copy over drive byte
+	movsb
+	; copy filename
+	mov ax, cs
+	mov ds, ax
+	mov si, bx
+	mov cx, 11
+	rep movsb
+	; done!
+	xor ax, ax
 	ret
+
 .err:	stc
+.ret:	sbb al, al
 	ret
 
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