sys: parse drive number and load BPB

Makefile

@@ -11,7 +11,7 @@ PRODUCT = rdos
 LABEL = $(PRODUCT) $(VERSION)
 
 NASM = nasm
-NASM_ARGS = -s -Ilib -DPRODUCT=$(PRODUCT) -DVERSION=$(VERSION)
+NASM_ARGS = -s -Ilib --before "cpu 8086" -DPRODUCT=$(PRODUCT) -DVERSION=$(VERSION)
 
 QEMU_ARGS += $(shell test -w /dev/kvm && echo --enable-kvm)
 
@@ -28,7 +28,7 @@ SYS = host/sys.elf
 FIXROM = host/fix-rom.elf
 
 .PHONY: default clean qemu-floppy5 qemu-floppy3
-.PRECIOUS: $(DISTFILES)
+.PRECIOUS: %.com
 
 default: fd1440.img
 
@@ -37,7 +37,7 @@ host/%.elf: host/%.c
 	$(CC) -o $@ $<
 
 # COM programs
-%.com: com/%.asm
+%.com: src/%.asm src/*.inc
 	$(NASM) $(NASM_ARGS) -o $@ $<
 
 # Bootloaders, first sector on partition
@@ -86,5 +86,8 @@ qemu-hdd: hdd.img $(ROMS)
 qemu-uartctrl: uartctrl.rom chartab.bs
 	$(QEMU) $(QEMU_ARGS) -option-rom uartctrl.rom -serial stdio -hda chartab.bs
 
-dosbox-%: %.com
+dosbox-%: %.com fd1440.img
-	dosbox -c "mount P $(CURDIR)" -c "P:" -c "$< $(ARGS)"
+	dosbox -c "mount P $(CURDIR)" -c "P:" -c "IMGMOUNT A: FD1440.IMG -t floppy" -c "$< $(ARGS)" -c "pause" -c "exit"
+
+emu2-%: %.com
+	emu2 $< $(ARGS)

src/@rdos.asm

@@ -0,0 +1,4 @@
+	mov ax, 0x0e38
+	int 0x10
+halt	hlt
+	jmp halt

src/parse.inc

@@ -0,0 +1,63 @@
+	; make a char uppercase
+	; IN	al	char
+	; OUT	al	char
+	; do nothing if >z
+ucase	cmp al, 0x7B
+	jnc .ret
+	; do nothing if <a
+	cmp al, 0x61
+	jc .ret
+	; do it!
+	sub al, 0x20
+.ret	ret
+
+	; read integer from ascii string
+	; default dec but allows 0x for hex
+	; bogus result if larger than 16 bit
+	; IN	ds:si	source string
+	;	cx	max number of chars
+	; OUT	ax	number
+	;	ds:si	first rejected char
+	;	cx	chars ignored
+lodnum	xor di, di
+	mov bx, 10
+	cmp cx, 2
+	jc .loop
+	; test for 0x prefix
+	mov ax, [si]
+	cmp al, 0x30
+	jne .loop
+	mov al, ah
+	call ucase
+	cmp al, 0x58
+	jne .loop
+	; apply 0x prefix
+.hex	add si, 2
+	sub cx, 2
+	mov bx, 0x10
+	; check if there are chars left
+.loop	test cx, cx
+	jnz .do
+.ret	mov ax, di
+	ret
+.do	mov al, [si]
+	call ucase
+	; check if in range
+	sub al, 0x30
+	jc .ret
+	cmp al, 0x10
+	jc .skip
+	sub al, 7
+	; must be smaller than base
+	; necessary to prevent hex digits in decimals
+.skip	mov ah, 0
+	cmp ax, bx
+	jnc .ret
+	; mark as read
+	inc si
+	dec cx
+	; add digit to number
+	xchg ax, di
+	mul bx
+	add di, ax
+	jmp .loop

src/print.inc

@@ -0,0 +1,75 @@
+	; print AX in base BX
+	; destroys DX
+putnum	xor dx, dx
+	div bx
+	test cx, cx
+	loopnz .pad
+	test ax, ax
+	je .nib
+.pad	push dx
+	call putnum
+	pop dx
+	; print lower DL as digit
+.nib	add dl, 0x30
+	cmp dl, 0x3a
+	jl putc
+	add dl, 7
+	; print DL as char
+putc	mov ah, 2
+	int 0x21
+	ret
+
+	; print str at SI
+	; NUL-terminated
+puts	lodsb
+	test al, al
+	jz .l01
+	mov dl, al
+	call putc
+	jmp puts
+.l01	ret
+
+	; print str at return addr
+	; NUL-terminated
+putsh	pop si
+	call puts
+	jmp si
+
+	; print a newline
+newlin	mov dl, 0x0A
+	call putc
+	mov dl, 0x0D
+	jmp putc
+
+	; print register set
+	; order AX CX DX BX BP SI DI IP
+	; trashes flags
+debug	push di
+	push si
+	push bp
+	push bx
+	push dx
+	push cx
+	push ax
+	mov si, sp
+	call dump
+	pop ax
+	pop cx
+	pop dx
+	pop bx
+	pop bp
+	pop si
+	pop di
+	ret
+
+	; dump the 8 words at SI
+dump	lea di, [si+16]
+	mov bx, 0x10
+.loop	lodsw
+	mov cx, 4
+	call putnum
+	mov dl, ' '
+	call putc
+	cmp si, di
+	jc .loop
+	jmp newlin

src/symbols.inc

@@ -0,0 +1,157 @@
+; implements a 6-byte symbol table
+; starts at s_end and grows down from there
+; all functions require DS=+CS
+
+s_start dw 0xC000 ; decreasing with usage
+s_end	dw 0xC000 ; const
+
+; incremented on freeing an entry
+; so we know if its worth searching
+s_gaps	db 0
+
+; allocate a symbol table entry
+; OUT	bx	ptr to entry
+s_alloc	mov bx, [s_start]
+	; check if its worth searching for a gap
+	cmp byte [s_gaps], 0
+	je .l04
+.l02	cmp bx, [s_end]
+	jnc .l01
+	; test if unallocated
+	cmp byte [bx], 0
+	jne .l03
+	; we found one! take note
+	dec byte [s_gaps]
+	jmp .l05
+.l03	add bx, 8
+	jmp .l02
+	; no gap found :/
+.l01	mov byte [s_gaps], 0
+	; extend symbol table at bottom
+.l04	mov bx, [s_start]
+	sub bx, 8
+	mov [s_start], bx
+	; insert default values
+.l05	mov [bx], dx
+	mov [bx+2], si
+	mov [bx+4], di
+	mov [bx+6], cx
+	clc
+	ret
+
+; free a symbol table entry
+; IN	bx	ptr to entry
+s_free	mov byte [bx], 0
+	inc byte [s_gaps]
+	ret
+
+; compare a table entry by string val
+; IN	bx	ptr to entry
+;	dx:si:di 6-byte ascii name, space padded
+; OUT	zero flag set if match
+s_comp	mov ax, [bx]
+	and ax, 0x7F7F
+	cmp ax, dx
+	jne .l01
+	mov ax, [bx+2]
+	and ax, 0x7F7F
+	cmp ax, si
+	jne .l01
+	mov ax, [bx+4]
+	and ax, 0x7F7F
+	cmp ax, di
+.l01	ret
+
+; fill in a backreference
+; IN	bx	ptr to tab entry
+;	cx	value
+s_bref	push bx
+	mov bx, [bx+6]
+	; todo: handle 8-bit relative backrefs
+	;add [output+bx], cx
+	pop bx
+	jmp s_free
+
+; set a symbol
+; IN	dx:si:di 6-byte ascii name, space padded
+;	cx	 value
+s_set	mov bx, [s_start]
+.loop	cmp bx, [s_end]
+	jnc .new
+	cmp byte [bx], 0
+	je .next
+	call s_comp
+	jne .l01
+	test byte [bx], 0x80
+	jnz .bref
+	stc
+	ret
+;	call s_prnt
+;	call errmsg
+;	db "DUP", 0
+.bref	call s_bref
+	jmp .next
+.l01	cmp dl, '.'
+	je .next
+	cmp byte [bx], '.'
+	jne .next
+	; delete local symbols if current set is non-local
+	call s_free
+.next	add bx, 8
+	jmp .loop
+.new	jmp s_alloc
+
+; get value of symbol
+; IN	dx:si:di 6-byte label
+; OUT 	carry	clear if label exists
+;	cx	symbol value, or 0 if not found
+s_get	mov bx, [s_start]
+.loop	cmp bx, [s_end]
+	jnc .fail
+	call s_comp
+	jnz .next
+	; skip if backref
+	test byte [bx], 0x80
+	jnz .next
+	mov cx, [bx+6]
+	clc
+	ret
+.next	add bx, 8
+	jmp .loop
+.fail	mov cx, 0
+	stc
+	ret
+
+; print out a table entry
+; IN	bx	ptr to entry
+s_prnt	mov dx, [bx]
+	call putc
+	mov dl, dh
+	call putc
+	mov dx, [bx+2]
+	call putc
+	mov dl, dh
+	call putc
+	mov dx, [bx+4]
+	call putc
+	mov dl, dh
+	call putc
+	mov dl, ' '
+	call putc
+	mov ax, [bx+6]
+	mov bx, 0x10
+	mov cx, 4
+	call putnum
+	jmp newlin
+
+; print out the full symbol table
+s_dump	mov bx, [s_start]
+.loop	cmp byte [bx], 0
+	je .next
+	push bx
+	call s_prnt
+	pop bx
+.next	add bx, 8
+	cmp bx, [s_end]
+	jc .loop
+	ret

src/sys.asm

@@ -0,0 +1,87 @@
+fcb1	equ 0x5C
+
+	org 0x100
+	jmp main
+
+%include "parse.inc"
+%include "print.inc"
+
+main	mov di, 0x81
+	mov al, 0x20
+	mov ch, 0
+	mov cl, [0x80]
+	repe scasb
+	repne scasb
+	mov si, di
+	call lodnum
+	mov dx, ax
+	test dx, ~0x83
+	jnz drverr
+	test dl, 0x80
+	jz floppy
+	call drverr
+
+drverr	call putsh
+	db "Failed to access drive", 0x0A, 0x0D, 0
+	int 0x20
+
+floppy	mov ax, 0x0201
+	mov cx, 0x0001
+	mov dh, 0
+	mov bx, bs
+	int 0x13
+	jc drverr
+	mov ax, [bs+0x18]
+	call debug
+	ret
+
+	mov dx, fcb1
+	mov ah, 0xF
+	int 0x21
+	test al, al
+	jz .fok
+.ferr	call putsh
+	db "Failed to read input file", 0x0A, 0x0D, 0
+	ret
+.fok	mov si, prog
+	; apply our target address
+.rloop	mov dx, si
+	mov ah, 0x1A
+	int 0x21
+	; increment address for next iteration
+	add si, 0x80
+	; do a read
+	mov dx, fcb1
+	mov ah, 0x14
+	int 0x21
+	; success: continue
+	cmp al, 0
+	jz .rloop
+	; eof: break
+	cmp al, 1
+	jz .cok
+	; segment wrap: fail
+	cmp al, 2
+	jz .ferr
+	; we assume al=3: eof
+.cok	nop
+	mov ax, si
+	sub ax, args
+	call debug
+	call putsh
+	db "yay", 0x0A,0x0D,0
+
+	ret
+;	mov ax, 0x0201
+;	mov cx, 0x0001
+;	mov dh, 0
+;	mov bx, bs
+;	int 0x13
+;	mov ax, [bs+0x18]
+;.ret	ret
+
+	align 2
+bs	equ $
+psp	equ bs + 0x200
+args	equ psp + 0x80
+prog	equ psp + 0x100

src/testsym.asm

@@ -0,0 +1,42 @@
+	jmp main
+
+%include "print.inc"
+%include "symbols.inc"
+
+	; OUT	cx	value of '$' label
+asmcur	mov cx, 0
+	ret
+
+	; IN	cx	runtime address
+	; OUT	es:bx	address in binary
+asmptr	mov bx, ds
+	mov es, bx
+	mov bx, cx
+	add bx, buf
+	ret
+
+main	call putsh
+	db "Normal read-back... ", 0
+
+	mov dx, "LA"
+	mov si, "BE"
+	mov di, "L1"
+	mov cx, 0x1234
+	call s_set
+	xor cx, cx
+
+	call s_get
+	cmp cx, 0x1234
+	call testz
+
+	ret
+
+testz	jnz .fail
+	call putsh
+	db "OK", 0x0A, 0x0D, 0
+	ret
+.fail	call putsh
+	db "FAIL", 0x0A, 0x0D, 0
+	ret
+
+buf	times 0x100 db 0