From a3ef6930597e0ea845fce0e803af6d154537ff32 Mon Sep 17 00:00:00 2001
From: Nero <41307858+nero@users.noreply.github.com>
Date: Fri, 10 Dec 2021 10:41:02 +0000
Subject: [PATCH] commit whatever is in my worktree rn

---
 com/@rdos.asm    |  38 +++--------
 com/a86.asm      | 163 ++++++-----------------------------------------
 kernel/drive.asm |  74 +++++++++++++--------
 kernel/fat.asm   | 125 ++++++++++++++++++++++++++++++++++++
 kernel/main.asm  |   8 +++
 5 files changed, 211 insertions(+), 197 deletions(-)
 create mode 100644 kernel/fat.asm
 create mode 100644 kernel/main.asm

diff --git a/com/@rdos.asm b/com/@rdos.asm
index 83e817a..2ce5368 100644
--- a/com/@rdos.asm
+++ b/com/@rdos.asm
@@ -7,11 +7,8 @@ banner:	db "RDOS KERNEL ", V, 0x0A, 0x0D, '$', 0x1A
 
 %include "kernel/far.asm"
 %include "kernel/char.asm"
-%include "inc/bpb.asm"
 %include "kernel/drive.asm"
-%include "kernel/fcb.asm"
-%include "kernel/rootdir.asm"
-%include "kernel/cluster.asm"
+%include "kernel/fat.asm"
 
 section .text
 
@@ -21,32 +18,15 @@ init:	call rstseg
 	mov dx, banner
 	call puts
 
-	call rstseg
-	mov dx, testdta
-	push ds
-	call norm
-	call setdta
-	pop ds
+	mov dl, 0
+	call select
 
-	mov dx, testfcb
-	call norm
-
-	call open
-
-	call read
-
-	mov ax, [cs:testdta]
-	mov cx, [cs:testdta+2]
-	int 3
+	mov dx, 3
+	call setclus
+	call rdfat
+	mov dx, bx
+	inc dx
+	call wdfat
 
 hlt:	hlt
 	jmp hlt
-
-section .data
-
-testfcb	db 0, "HELLO   ","COM"
-	times FCBSIZ db 0
-
-section .bss
-
-testdta	resb 128
diff --git a/com/a86.asm b/com/a86.asm
index c227117..2c50896 100644
--- a/com/a86.asm
+++ b/com/a86.asm
@@ -43,10 +43,6 @@ dmpdx3:	int 0x10
 free	dw 0 ; free ram size
 lncnt	dw 0 ; line count
 rdptr	dw 0xFFFF ; infile blk ptr
-symbol	dw 0 ; symbol of current line
-offset	dw 0 ; byte offset in outfile
-len	db 0 ; len for wrd (must be before it)
-wrd	dw 0,0,0,0,0,0,0,0 ; 16 byte word buf
 
 getc	mov bx, [rdptr]
 	cmp bx, 0x80
@@ -72,12 +68,6 @@ l02	mov al, 0x1A
 l03	cmp al, eof
 	ret
 
-;getc2	call peek
-;	cmp al, eof
-;	jne getc_
-;	inc word [rdptr]
-;getc_	ret
-
 newlin	mov dl, 0x0A
 	mov ah, 2
 	int 0x21
@@ -99,145 +89,32 @@ error	mov dl, [bx]
 e_eof	db "EOF "
 e_dup	db "DUPSYM "
 
-	; scan word
-scawrd	mov si, wrd
-l04	call getc
-	; EOF is fatal
-	mov bx, e_eof
-	jz error
-	; tab=end
-	cmp al, 9
-	je pad
-	; space=end
-	cmp al, 0x20
-	je pad
-	; if lbl full, continue eating
-	cmp si, wrd+0x10
-	jnc l04
-	; insert
-	mov [si], al
-	inc si
-	jmp l04
-	; pad with spaces
-pad	mov cx, si
-	sub cx, wrd
-	mov [len], cl
-	cmp si, wrd+0x10
-	jnc l06
-	mov ah, 0x20
-	xchg ah, [si]
-	inc si
-	cmp ah, 0x20
-	jne pad
-l06	ret
+tok1:
+s_ws	db " " ; also used for tabs
+s_com	db ","
+s_obr	db "["
+s_cbr	db "]"
+s_plu	db "+"
+s_min	db "-"
 
-	; print wrd
-dmpwrd	mov si, wrd
-	mov cx, 0x10
-	mov ah, 2
-l05	mov dl, [si]
-	cmp dl, 0x20
-	je l07
-	inc si
-	int 0x21
-	loop l05
-l07	call newlin
-	ret
+	align 2
+tok2:
+reg8	db "AL","CL","DL","BL","AH","CH","DH","BH"
+reg16	db "AX","CX","DX","BX","SP","BP","SI","DI"
+sreg	db "ES","CS","SS","DS"
+s_db	db "DB"
+s_dw	db "DW"
 
-	; create symbol table entry
-	; name is read from [wrd]
-	; offset is written to [symbol]
-symins	cmp byte [wrd], 0x20
-	je nosym
-	mov bx, init ; walk ptr
-	mov bp, [free]
-	add bp, bx ; end addr
-	jmp l09
-l08	add bx, 8
-l09	mov al, [bx]
-	cmp al, 0
-	je l10
-	call symcmp
-	jnz l08
-	mov bx, e_dup
-	jmp error
-	; copy str to table
-l10	mov si, wrd
-	mov di, bx
-	movsw
-	movsw
-	movsw
-	xor ax, ax
-	stosw
-	mov byte [bx+8], 0
-	mov [symbol], bx
-	ret
+tok3:
+s_org	db "ORG"
+s_equ	db "EQU"
 
-nosym	xor ax, ax
-	mov [symbol], ax
-	ret
-
-	; compares 6 bytes [bx] with [wrd]
-	; bit 7 of each byte is ignored
-symcmp	mov si, wrd
-	xor ax, ax
-	mov dx, [wrd]
-	xor dx, [bx]
-	or ax, dx
-	mov dx, [wrd+2]
-	xor dx, [bx+2]
-	or ax, dx
-	mov dx, [wrd+4]
-	xor dx, [bx+4]
-	or ax, dx
-	test ax, 0x8F8F
-	ret
-
-	; look up keyword in wrd
-	; result is stored in bx
-lookup	mov ch, 0
-	mov bx, s_org
-l11	mov si, bx
-	mov di, len ; wrd immediately follows
-	mov cl, [bx]
-	test cx, cx
-	jz l13
-	inc cl
-	mov dx, cx
-	rep cmpsb
-	je l12
-	add bx, dx
-	jmp l11
-	; found!
-l12	clc
-	ret
-	; give up
-l13	xor bx, bx
-	stc
-	ret
-
-s_org	db 3, "org"
-s_equ	db 3, "equ"
-	db 0
+	; TODO: parse a line into wordlist of tokens and ptrs to strings
+rline:	ret
 
 	; clear symbol table
 main	mov byte [init], 0
-	; scan and create label
-mloop	call scawrd
-	call symins
-	; scan instruction word
-	call scawrd
-	call lookup
-	; special stuff
-	cmp bx, s_org
-	je iorg
-	mov ax, bx
-	call dumpax
-	int 0x20
-
-	; org pseudo instruction
-iorg	mov ax, 0x5A5A
-	call dumpax
+	call rline
 	int 0x20
 
 	align 16
diff --git a/kernel/drive.asm b/kernel/drive.asm
index 248dfc5..75b9aa5 100644
--- a/kernel/drive.asm
+++ b/kernel/drive.asm
@@ -5,6 +5,34 @@
 ; - dirty: inform that dskbuf has been written to
 ; access is done by accessing dskbuf directly
 
+BPBOFF	equ 0xB
+
+; DOS 2.0 BPB
+BPBSS	equ 0 ; word
+BPBSC	equ 2 ; byte
+BPBRSC	equ 3 ; word
+BPBFN	equ 5 ; byte
+BPBRDE	equ 6 ; word
+BPBTS	equ 8 ; word
+BPBMD	equ 10 ; byte
+BPBFS	equ 11 ; word
+BPBSIZ2	equ 13 ; size constant
+
+; DOS 3.31 BPB
+BPBSPT	equ 0x0D ; word
+BPBNOS	equ 0x0F ; word
+BPBHS	equ 0x11 ; dword
+BPBLTS	equ 0x15 ; dword
+BPBSIZ3	equ 25 ; size constant
+
+; DOS 3.4 EBPB
+BPBDN	equ 0x19 ; byte
+BPBFALG	equ 0x1A ; byte
+BPBSIG	equ 0x1B ; byte
+BPBSER	equ 0x1C ; dword serial number
+BPBSIZ4	equ 32 ; size constant
+
+; Disk parameter table (int 1E)
 DPTSIZE	equ 11
 DPTSPT	equ 4
 
@@ -94,10 +122,10 @@ getprm	test byte [dskflag], 4
 	call lodfar
 .ret	ret
 
-	; log in drive
+	; select a drive for io
 	; IN	dl	drive number
 	; dont do anything if drive already selected
-logdrv	cmp dl, [dsknum]
+select	cmp dl, [dsknum]
 	je logfdd.ret
 	; clear out current contents
 	push dx
@@ -191,35 +219,42 @@ loghdd	sub dl, 2
 logerr	stc
 	ret
 
-	; count from partition start
+	; map sector into dskbuf
+	; sector number from partition start
 	; IN	dx:ax	sector number
-maprel	add ax, [bpb+BPBHS]
+map	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 dskread
+	jne l003
 	cmp dx, [dskseek+2]
-	jne dskread
-	ret
-
-dskread	push ax
+	je l002
+	; flush and read other sector
+l003	push ax
 	push dx
 	call flush
 	pop dx
 	pop ax
 	; store the sector number
-	mov [cs:dskseek], ax
-	mov [cs:dskseek+2], dx
-	; do the actual read
+	mov [dskseek], ax
+	mov [dskseek+2], dx
+	jmp _read
 
+	; mark dskbuf as containing unwritten changes
+dirty	or byte [cs:dskflag], 1 ; dirty
+l002	ret
+
+	; flush buffer if dirty
+flush	test byte [cs:dskflag], 1
+	jz l002
 	; low level read and write
 	; call again to retry, no input registers
 	; read or write is configured in cx
-_read	mov ch, 2
-	db 0x3D ; cmp ax, imm16: causes next instr to be skipped
 _write	mov ch, 3
+	db 0x3D ; cmp ax, imm16: causes next 2 bytes to be skipped
+_read	mov ch, 2
 	mov cl, 1 ; read len
 	; DS := ES := CS
 	mov ax, cs
@@ -286,14 +321,3 @@ _write	mov ch, 3
 	; exit with carry flag set
 	stc
 	ret
-
-	; mark dskbuf as containing unwritten changes
-dirty	or byte [cs:dskflag], 1 ; dirty
-	ret
-
-	; flush buffer if dirty
-flush	test byte [cs:dskflag], 1
-	jz .ret
-	; TODO: error handling & retries
-	jmp _write
-.ret	ret
diff --git a/kernel/fat.asm b/kernel/fat.asm
new file mode 100644
index 0000000..aad99bb
--- /dev/null
+++ b/kernel/fat.asm
@@ -0,0 +1,125 @@
+section .bss
+
+clus	resw 1
+
+section .text
+
+	; Set cluster for next operations
+	; IN	dx	cluster number
+setclus	mov [clus], dx
+	ret
+
+	; get ptr to single byte in fat table
+	; IN	dx	position byte in fat table
+	; OUT	bx	ptr to byte in dskbuf
+_fat1	push dx
+	mov ax, dx
+	xor dx, dx
+	mov cl, 9
+	shr ax, cl
+	add ax, [bpb+BPBRSC]
+	adc dx, 0
+	call map
+	pop dx
+	mov bx, dx
+	and bx, 0x1FF
+	add bx, dskbuf
+	ret
+
+	; get ptr to word in fat table
+_fat2	push dx
+	mov ax, dx
+	xor dx, dx
+	mov cl, 8
+	shr ax, cl
+	add ax, [bpb+BPBRSC]
+	adc dx, 0
+	call map
+	pop dx
+	mov bl, dl
+	mov bh, 0
+	add bx, bx
+	add bx, dskbuf
+	ret
+
+	; read value from fat table
+	; index given with setclus
+	; OUT	bx	value
+	;	carry	set if EOF marker
+rdfat	mov dx, [clus]
+	mov ax, dx
+	shr ax, 1
+	add dx, ax
+	call _fat1
+	push word [bx]
+	inc dx
+	call _fat1
+	mov si, bx
+	pop bx
+	mov bh, [si]
+	test word [clus], 1
+	jz l001
+	mov cl, 4
+	shr bx, cl
+l001	and bx, 0xFFF
+	cmp bx, 0xFF0
+	cmc
+	ret
+
+	; set value in FAT table
+	; IN	dx	value
+wrfat	and dh, 0x0F
+	push dx
+	; DX = index * 1.5
+	mov dx, [clus]
+	mov ax, dx
+	shr dx, 1
+	add dx, ax
+	call _fat1
+	pop ax
+	test [clus], 1
+	jnz l004
+	; even, first byte full
+	mov [bx], al
+	push ax
+	call dirty
+	; DX = index * 1.5
+	mov dx, [clus]
+	mov ax, dx
+	shr dx, 1
+	add dx, ax
+	inc dx
+	call _fat1
+	pop ax
+	mov al, [bx]
+	and al, 0xF0
+	or al, ah
+	mov [bx], al
+	call dirty
+	jmp l005
+	; odd, second byte full
+l004:	mov ch, [bx]
+	; concat existing and our nib
+	and ch, 0x0F
+	mov cl, 4
+	shl ax, cl
+	or al, ch
+	; write back lower 4 bits
+	mov [bx], al
+	call dirty
+	push ax
+	; re-calculate offset
+	mov ax, dx
+	shr dx, 1
+	add dx, ax
+	inc dx
+	; map second byte
+	call _fat1
+	pop ax
+	; write higher 8 bits
+	mov [bx], ah
+	call dirty
+l005:	ret
+
+	; wrfat from above, FAT16 flavour
+wf16:	ret
diff --git a/kernel/main.asm b/kernel/main.asm
new file mode 100644
index 0000000..19a325e
--- /dev/null
+++ b/kernel/main.asm
@@ -0,0 +1,8 @@
+	org 0
+	jmp init
+
+init:	mov ax, 0x0e37
+	int 0x10
+
+hlt:	hlt
+	jmp hlt