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Restructure kernel to use 1-segment COM convention

This commit is contained in:
Nero 2021-02-07 16:17:31 +00:00
parent 71c89387fc
commit 84b754551c
7 changed files with 369 additions and 448 deletions
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6
Makefile
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@ -1,5 +1,5 @@
PROGRAMS = hello.com PROGRAMS = hello.com
DISTFILES = kernel.bs $(PROGRAMS) DISTFILES = @rdos.com $(PROGRAMS)
ROMS = ROMS =
QEMU = qemu-system-i386 QEMU = qemu-system-i386
@ -43,7 +43,7 @@ host/%.elf: host/%.c
%.bs: boot/%.asm %.bs: boot/%.asm
$(NASM) $(NASM_ARGS) -o $@ $< $(NASM) $(NASM_ARGS) -o $@ $<
kernel.bs: kernel/*.asm @rdos.com: kernel/*.asm
# Special case: variations of FAT vbr # Special case: variations of FAT vbr
fat1.bs: boot/fat.asm fat1.bs: boot/fat.asm
@ -62,7 +62,7 @@ fat6.bs: boot/fat.asm
fd%.img: $(DISTFILES) $(SYS) fd%.img: $(DISTFILES) $(SYS)
mformat -C -i $@ -f $* -c 2 -v "$(LABEL)" :: mformat -C -i $@ -f $* -c 2 -v "$(LABEL)" ::
mcopy -i $@ $(DISTFILES) :: mcopy -i $@ $(DISTFILES) ::
$(SYS) $@ hello.com $(SYS) $@ @rdos.com
clean: clean:
rm -f *.com *.bs *.0 *.lst *.img *.bin *.rom rm -f *.com *.bs *.0 *.lst *.img *.bin *.rom

107
boot/kernel.asm
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@ -1,107 +0,0 @@
cpu 8086
org 0x0700
%include "inc/bpb.asm"
%include "inc/mbr.asm"
%include "inc/dpt.asm"
init: cli
xor ax, ax
mov ds, ax
mov es, ax
mov ss, ax
mov sp, ax
mov si, 0x7C00
; relocate to 00700
mov di, text_start
mov cx, text_length + rodata_length + data_length
rep movsb
; clear out bss section
mov cx, bss_length
rep stosb
; jump to copy
call 0:relinit
section .rodata
%define V 0x %+ VERSION
version: dd V
section .text
relinit: ; print banner
push word [version]
push word [version+2]
call printf
db "RDOS ",2,2, 0x0A, 0x0D, 0
; initialize the disk i/o
call dinit
; init 21h vector
mov word [0x21*4], int21
mov word [0x21*4+2], cs
; set current PSP, directly after us
mov ax, stack
mov cl, 4
shr ax, cl
mov word [curpsp], ax
; also the DTA
mov bx, dta
call setdta
; set current drive to boot drive
mov al, dl
rol al, 1
rol al, 1
or dl, al
and dl, 3
call setdd
mov bx, testfcb
call fndfst
restart:
hlt: hlt
jmp hlt
%include "kernel/psp.asm"
%include "kernel/syscall.asm"
%include "kernel/char.asm"
%include "kernel/fcb.asm"
%include "kernel/drive.asm"
%include "kernel/printf.asm"
section .bss
dta: resb 128
section .data
testfcb: db 0
db "HELLO ", "COM"
times 30 db 0
section .text
text_start equ $$
text_length equ $-$$
section .rodata
rodata_start equ $$
rodata_length equ $-$$
section .data
data_start equ $$
data_length equ $-$$
section .bss
resw 256 ; 512b kern stack
alignb 16
stack: ; stack grows into this ^
; this is also the end marker
; programs with their psp start here
bss_start equ $$
bss_length equ $-$$

38
com/@rdos.asm Normal file
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@ -0,0 +1,38 @@
org 0x100
jmp init
%defstr V VERSION
banner: db "RDOS ", V, 0x0A, 0x0D, 0, 0x1A
%include "kernel/far.asm"
%include "inc/bpb.asm"
%include "kernel/drive.asm"
section .text
init: call rstseg
mov si, banner
.l01: lodsb
test al, al
jz .l02
mov ah, 0x0e
xor bx, bx
int 0x10
jmp .l01
.l02:
call dinit
mov dl, 0
call logdrv
xor ax, ax
xor dx, dx
call maprd
inc word [dskbuf+0x80]
call dirty
call flush
hlt: hlt
jmp hlt

16
host/sys.c
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@ -117,14 +117,14 @@ int main(int argc, char** argv) {
char* putsfunc = ptr; char* putsfunc = ptr;
// assemble puts function // assemble puts function
ptr = push_imm16(ptr, 0xAC5E); //ptr = push_imm16(ptr, 0xAC5E);
ptr = push_imm16(ptr, 0xC084); //ptr = push_imm16(ptr, 0xC084);
ptr = push_imm16(ptr, 0x0874); //ptr = push_imm16(ptr, 0x0874);
ptr = push_imm16(ptr, 0x0EB4); //ptr = push_imm16(ptr, 0x0EB4);
ptr = push_imm16(ptr, 0xDB31); //ptr = push_imm16(ptr, 0xDB31);
ptr = push_imm16(ptr, 0x10CD); //ptr = push_imm16(ptr, 0x10CD);
ptr = push_imm16(ptr, 0xF3EB); //ptr = push_imm16(ptr, 0xF3EB);
ptr = push_imm16(ptr, 0xE6FF); //ptr = push_imm16(ptr, 0xE6FF);
// assemble entry point to our main code // assemble entry point to our main code
push_jmp(bs, ptr); push_jmp(bs, ptr);

5
inc/dpt.asm
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@ -1,5 +0,0 @@
DPTMTT equ 2
DPTSS equ 3
DPTSPT equ 4
DPTSIZE equ 11

203
kernel/drive.asm
View File

@ -5,78 +5,68 @@
; - dirty: inform that dskbuf has been written to ; - dirty: inform that dskbuf has been written to
; access is done by accessing dskbuf directly ; access is done by accessing dskbuf directly
DPTSIZE equ 11
DPTSPT equ 4
section .bss section .bss
; drive actually selected for I/O
dsknum: resb 1
; bios drive we end up using ; bios drive we end up using
biosnum: resb 1 biosnum resb 1
dap: resw 2
.buf: resw 2
; current sector number
; absolute, ignores partition
dskseek: resd 2
; bit 0 (1) - dirty flag for dskbuf ; bit 0 (1) - dirty flag for dskbuf
; bit 1 (2) - controller configured ; bit 1 (2) - controller configured
; bit 2 (4) - EBIOS supported ; bit 2 (4) - EBIOS supported
dskflag: resb 1 dskflag resb 1
; disk buffer for I/O operations ; disk buffer for I/O operations
dskbuf: resb 512 dskbuf resb 512
dpt: resb DPTSIZE dpt resb DPTSIZE
bpb: resb BPBSIZ4 bpb resb BPBSIZ4
section .data
; drive actually selected for I/O
dsknum db 0xFF
dap db 0x10, 0
dw 1
dapbuf dw dskbuf, 0
dskseek dw 0,0,0,0
section .text section .text
; initial setup for disk i/o ; initial setup for disk i/o
dinit: ; copy previously set DPT to our data area ; copy previously set DPT to our data area
push ds dinit xor ax, ax
push cs mov es, ax
pop es les bx, [es:4*0x1E]
lds si, [es:4*0x1E] mov dx, dpt
mov di, dpt
mov cx, 11 mov cx, 11
rep movsb call lodfar
; set vector ; set interrupt vector
mov word [cs:4*0x1E], dpt mov es, cx
mov word [cs:4*0x1E+2], ds mov word [es:4*0x1E], dpt
; set to invalid drive mov word [es:4*0x1E+2], ds
mov byte [cs:dsknum], 0xFF ; set segment addr in DAP
pop ds mov [dapbuf+2], cs
ret ret
; int 13 stub ; int 13 stub
int13: ; debug output ; this is meant as a central place to implement
push bx ; stack switching or some other safeguards
push dx int13 int 0x13
push cx
push ax
call printf
db "int13 CALL AX=",2," CX=",2," DX=",2," BX=",2,0x0A,0x0D,0
; do the call
int 0x13
jc .err
ret
.err: push ax
call printf
db "DISK ERR AX=",2,0x0A,0x0D,0
stc
ret ret
; get drive parameters ; get drive parameters
; read BIOS int13h/AH=8 values ; read BIOS int13h/AH=8 values
; DPT data gets copied over our dpt ; DPT data gets copied over our dpt
; CHS data gets inserted into our bpb ; CHS data gets inserted into our bpb
getprm: ; skip if EBIOS extension enabled getprm test byte [dskflag], 4
test byte [cs:dskflag], 4
jnz .ret jnz .ret
; do the query ; do the query
mov ah, 8 mov ah, 8
mov dl, [cs:biosnum] mov dl, [biosnum]
call int13 call int13
; bail out if error ; bail out if error
jc .ret jc .ret
@ -85,43 +75,31 @@ getprm: ; skip if EBIOS extension enabled
jz .nochs jz .nochs
; get and store sector number ; get and store sector number
and cx, 0x3F and cx, 0x3F
mov word [cs:bpb+BPBSPT], cx mov word [bpb+BPBSPT], cx
; get and store number of heads ; get and store number of heads
xchg dl, dh xchg dl, dh
and dx, 0xFF and dx, 0xFF
inc dx inc dx
mov [cs:bpb+BPBNOS], dx mov [bpb+BPBNOS], dx
; test if DPT ptr is non-zero ; test if DPT ptr is non-zero
.nochs: mov ax, es .nochs mov ax, es
or ax, di or ax, di
test ax, ax test ax, ax
jz .ret jz .ret
; DS:SI = ES:DI ; copy BIOS dpt table over ours
mov ax, es mov dx, dpt
mov ds, ax mov bx, di
mov si, di call lodfar
; ES:DI = dpt .ret ret
xor ax, ax
mov es, ax
mov di, dpt
; do the copy
mov cx, 11
rep movsb
.ret: ret
; log in drive ; log in drive
; IN dl drive number ; IN dl drive number
logdrv: ; DS := CS
push cs
pop ds
; dont do anything if drive already selected ; dont do anything if drive already selected
cmp dl, [dsknum] logdrv cmp dl, [dsknum]
je logfdd.ret je logfdd.ret
; clear out current contents ; clear out current contents
push dx push dx
push ds
call flush call flush
pop ds
mov ax, 0xFFFF mov ax, 0xFFFF
mov [dskseek], ax mov [dskseek], ax
mov [dskseek+2], ax mov [dskseek+2], ax
@ -133,25 +111,20 @@ logdrv: ; DS := CS
cmp dl, 2 cmp dl, 2
jnc loghdd jnc loghdd
logfdd: ; save info for bios ; save info for bios
mov [biosnum], dl logfdd mov [biosnum], dl
; reset dpt to defaults ; reset dpt to defaults
push ds
call getprm call getprm
pop ds
; set default geometry (1.44 MB floppy) ; set default geometry (1.44 MB floppy)
mov word [bpb+BPBNOS], 2 mov word [bpb+BPBNOS], 2
mov word [bpb+BPBSPT], 18 mov word [bpb+BPBSPT], 18
; load boot sector ; load boot sector
push ds
xor ax, ax xor ax, ax
xor dx, dx xor dx, dx
call mapabs call mapabs
pop ds
; copy bios parameter block ; copy bios parameter block
; TODO: guess from first byte of FAT if BPB invalid ; TODO: guess from first byte of FAT if BPB invalid
push ds call rstseg
pop es
mov si, dskbuf+BPBOFF mov si, dskbuf+BPBOFF
mov di, bpb mov di, bpb
mov cx, BPBSIZ4 mov cx, BPBSIZ4
@ -163,10 +136,9 @@ logfdd: ; save info for bios
xor ax, ax xor ax, ax
mov [bpb+BPBHS], ax mov [bpb+BPBHS], ax
mov [bpb+BPBHS+2], ax mov [bpb+BPBHS+2], ax
.ret: ret .ret ret
; assumes that DS == CS loghdd sub dl, 2
loghdd: sub dl, 2
cmp dl, 4 cmp dl, 4
jnc logerr jnc logerr
push dx push dx
@ -180,16 +152,8 @@ loghdd: sub dl, 2
jnz .chs jnz .chs
; enable ebios and assume controller is configured ; enable ebios and assume controller is configured
or byte [dskflag], (2+4) or byte [dskflag], (2+4)
; initialize DAP
mov word [dap], 0x10
mov word [dap+2], 1
mov word [dap+4], dskbuf
xor ax, ax
mov word [dap+6], ax
mov word [dap+12], ax
mov word [dap+14], ax
; get chs data (needed or we cant load vbr) ; get chs data (needed or we cant load vbr)
.chs: call getprm .chs call getprm
; read mbr ; read mbr
xor ax, ax xor ax, ax
xor dx, dx xor dx, dx
@ -200,20 +164,17 @@ loghdd: sub dl, 2
mov cl, 4 mov cl, 4
sal bx, cl sal bx, cl
; bail out if no partition ; bail out if no partition
cmp byte [cs:dskbuf+0x1be+bx+4], 0 cmp byte [dskbuf+0x1be+bx+4], 0
je logerr je logerr
; load partition offset ; load partition offset
mov ax, [cs:dskbuf+0x1be+bx+8] mov ax, [dskbuf+0x1be+bx+8]
mov dx, [cs:dskbuf+0x1be+bx+8+2] mov dx, [dskbuf+0x1be+bx+8+2]
; save to to stack ; save to to stack
push dx push dx
push ax push ax
; load vbr ; load vbr
call mapabs call mapabs
; copy bpb ; copy bpb
mov ax, cs
mov ds, ax
mov es, ax
mov si, dskbuf+BPBOFF mov si, dskbuf+BPBOFF
mov di, bpb mov di, bpb
mov cx, BPBSIZ4 mov cx, BPBSIZ4
@ -221,44 +182,44 @@ loghdd: sub dl, 2
; fix CHS data ; fix CHS data
call getprm call getprm
; fix partition offset ; fix partition offset
pop ax pop word [bpb+BPBHS]
pop dx pop word [bpb+BPBHS+2]
mov [cs:bpb+BPBHS], ax ;pop [bpb+BPBNOS]
mov [cs:bpb+BPBHS+2], dx ;pop [bpb+BPBSPT]
ret ret
logerr: stc logerr stc
ret ret
mapclu: ; counting from begin of cluster area ; counting from begin of cluster area
mov bx, [cs:bpb+BPBRDE] mapclu mov bx, [bpb+BPBRDE]
mov cl, 4 mov cl, 4
shr bx, cl ; 32 bytes per entry shr bx, cl ; 32 bytes per entry
add ax, bx add ax, bx
adc dx, 0 adc dx, 0
maprd: ; counting from beginning of dir ; counting from beginning of dir
; add fat table sizes ; add fat table sizes
xor ch, ch maprd xor ch, ch
mov cl, byte [cs:bpb+BPBFN] mov cl, byte [bpb+BPBFN]
.loop: add ax, [cs:bpb+BPBFS] .loop add ax, [bpb+BPBFS]
adc dx, 0 adc dx, 0
loop .loop loop .loop
mapfat: ; counting from beginning of FAT ; counting from beginning of FAT
; add reserved sector count ; add reserved sector count
add ax, [cs:bpb+BPBRSC] mapfat add ax, [bpb+BPBRSC]
adc dx, 0 adc dx, 0
map: ; count from partition start ; count from partition start
add ax, [cs:bpb+BPBHS] map add ax, [bpb+BPBHS]
add dx, [cs:bpb+BPBHS+2] add dx, [bpb+BPBHS+2]
mapabs: ; absolute sector count ; absolute sector count
; skip doing a read if sector number matches ; skip doing a read if sector number matches
cmp ax, [cs:dskseek] mapabs cmp ax, [dskseek]
jne read jne read
cmp dx, [cs:dskseek+2] cmp dx, [dskseek+2]
jne read jne read
ret ret
read: push ax read push ax
push dx push dx
call flush call flush
pop dx pop dx
@ -271,9 +232,9 @@ read: push ax
; low level read and write ; low level read and write
; call again to retry, no input registers ; call again to retry, no input registers
; read or write is configured in cx ; read or write is configured in cx
_read: mov ch, 2 _read mov ch, 2
db 0x3D ; cmp ax, imm16: causes next instr to be skipped db 0x3D ; cmp ax, imm16: causes next instr to be skipped
_write: mov ch, 3 _write mov ch, 3
mov cl, 1 ; read len mov cl, 1 ; read len
; DS := ES := CS ; DS := ES := CS
mov ax, cs mov ax, cs
@ -287,14 +248,14 @@ _write: mov ch, 3
mov si, dap mov si, dap
jmp .do jmp .do
; check if we can skip controller reset ; check if we can skip controller reset
.l00: test byte [dskflag], 2 .l00 test byte [dskflag], 2
jnz .l01 jnz .l01
; do controller reset ; do controller reset
mov dl, [biosnum] mov dl, [biosnum]
mov ah, 0 mov ah, 0
call int13 call int13
or byte [dskflag], 2 or byte [dskflag], 2
.l01: ; put sectors per cylinder into bx .l01 ; put sectors per cylinder into bx
mov ax, [bpb+BPBSPT] mov ax, [bpb+BPBSPT]
mul word [bpb+BPBNOS] mul word [bpb+BPBNOS]
mov bx, ax mov bx, ax
@ -322,7 +283,7 @@ _write: mov ch, 3
xchg cx, dx xchg cx, dx
xchg dh, dl xchg dh, dl
mov bx, dskbuf mov bx, dskbuf
.do: mov dl, [biosnum] .do mov dl, [biosnum]
; ah: subfunction selected via cx previously ; ah: subfunction selected via cx previously
; al: 1 = reading 1 sector ; al: 1 = reading 1 sector
; cx: sector and cylinder number ; cx: sector and cylinder number
@ -335,19 +296,19 @@ _write: mov ch, 3
and byte [dskflag], 0xFE and byte [dskflag], 0xFE
clc clc
ret ret
.err: ; assume controller is misconfigured .err ; assume controller is misconfigured
and byte [dskflag], 0xFD and byte [dskflag], 0xFD
; exit with carry flag set ; exit with carry flag set
stc stc
ret ret
; mark dskbuf as containing unwritten changes ; mark dskbuf as containing unwritten changes
dirty: or byte [cs:dskflag], 1 ; dirty dirty or byte [cs:dskflag], 1 ; dirty
ret ret
; flush buffer if dirty ; flush buffer if dirty
flush: test byte [cs:dskflag], 1 flush test byte [cs:dskflag], 1
jz .ret jz .ret
; TODO: error handling & retries ; TODO: error handling & retries
jmp _write jmp _write
.ret: ret .ret ret

34
kernel/far.asm Normal file
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@ -0,0 +1,34 @@
; reset segments
rstseg mov ax, cs
mov ds, ax
mov es, ax
ret
; copy to far memory
; IN es:bx far memory ptr (preserved)
; ds:dx local ptr (preserved)
; cx number of bytes to transfer
; OUT cx set to zero
; si & di trashed
stofar mov si, dx
mov di, bx
rep movsb
ret
; copy from far memory
; IN es:bx far memory ptr (preserved)
; ds:dx local ptr (preserved)
; cx number of bytes to copy
; OUT cx set to zero
; si & di trashed
lodfar call xchgdes
mov si, bx
mov di, dx
rep movsb
; exchange es and ds
xchgdes push ds
push es
pop ds
pop es
ret