Split out kernel components in kernel/
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2d949a01f8
commit
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2
Makefile
2
Makefile
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@ -48,6 +48,8 @@ vga11.com: cp437.bin
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%.bs: boot/%.asm
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$(NASM) $(NASM_ARGS) -o $@ $<
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kernel.bs: kernel/*.asm
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# Special case: variations of FAT vbr
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fat1.bs: boot/fat.asm
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$(NASM) $(NASM_ARGS) -DFAT12 -DCHS -o $@ $<
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195
boot/kernel.asm
195
boot/kernel.asm
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@ -10,8 +10,8 @@
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%endmacro
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; Far jump via interrupt vector
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%macro intjump 1
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jump far [cs:%1*4]
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%macro intjmp 1
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jmp far [cs:%1*4]
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%endmacro
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; stack size
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@ -22,7 +22,7 @@ banner: db "rdos", 0xA, 0xD, '$'
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; Alias for Int 21h,AH=0h
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int20h: xor ah, ah
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; allow extenders to get away with only hooking 21h
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jmp [cs:(0x21 * 4)]
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intjmp 0x21
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int21h: ; inside of kernel, direction always goes up
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; the iret will restore it to the user value later
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@ -48,6 +48,7 @@ iretfl: push ax
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pop ax
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; iret frame: IP CS FLAGS
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iret: iret
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retf: retf
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; Subfunction ptr
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; this is used as extra register in int21h
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@ -171,185 +172,6 @@ getint: xor bx, bx
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sferr: stc
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ret
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; Convert between drive number and BIOS dl
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; Bidirectional mapping
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; 0 <-> 0, 1 <-> 1, 2 <-> 0x80, 3 <-> 0x81
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dnconv: mov cx, 7
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ror dx, 1
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rol dl, 1
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dncl: rcl dl, 1
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rcr dh, 1
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loop dncl
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xchg dh, dl
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ret
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; Set sector number
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seek: mov [drvpos], ax
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mov [drvpos+2], dx
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ret
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; Read sector from disk
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read: ; this uses the EBIOS extensions
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; qword sector number
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xor ax, ax
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push ax
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push ax
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mov ax, [cs:drvpos+2]
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push ax
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mov ax, [cs:drvpos]
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push ax
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; dword target buffer
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mov ax, buffer
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push cs
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push ax
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; word number of sectors
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mov ax, 1
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push ax
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; size & passing
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mov di, 0x10
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push di
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mov si, sp
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mov ah, 0x42
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mov dl, [cs:drvnum]
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call dnconv
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stc
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int 0x13
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add sp, di
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ret
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; Select active drive
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; IN dl drive number A=0, B=1, C=2, ...
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select: mov [cs:drvnum], dl
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ret
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push es
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xor ax, ax
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push cs
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pop es
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mov si, drvoff
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stosw
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stosw
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stosw
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stosw
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pop es
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call read
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; load bpb from buffer to bpb
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ldbpb: push ds
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push es
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mov ax, cs
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mov ds, ax
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mov es, ax
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mov si, buffer+0x0B
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mov di, bpb
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mov cx, bpb_len
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rep movsb
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pop es
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pop ds
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ret
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; defines for CHS table
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chs_spt: equ 0 ; word sectors per track
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chs_nos: equ 2 ; word number of sides
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chs_po: equ 4 ; dword partition offset
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chs_siz: equ 8
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fndchs: ; find CHS table entry
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; IN dl DOS drive number (A=0, B=1, ...)
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; OUT cs:si ptr to chs table entry
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push ax
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mov ax, chs_siz
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mul dl
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add ax, chstab
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mov si, ax
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pop ax
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ret
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; compare sector number in disk access packet with zero
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; sets zero flag accordingly
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iszero: push ax
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mov ax, [bx]
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or ax, [bx+2]
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pop ax
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ret
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; calculate CHS from dap and CHS table entry
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; IN ds:bx disk access packet
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; cs:si chstab table entry
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; OUT cx,dh chs data for int 13h
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calchs: push ax
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; load linear sector number
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mov dx, [bx+2]
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mov ax, [bx]
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; if any word of it is non-zero, we need to do calculation
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call iszero
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jz .zero
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; ax is track number (lba / spt)
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; dx is sector (lba % spt) + 1
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div word [cs:si+chs_spt]
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inc dx
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; sector number
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mov cl, dl
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; ax is cylinder (track / heads)
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; dx is head (track % heads)
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xor dx, dx
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div word [cs:si+chs_nos]
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; set up cylinder and head number
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mov ch, al
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mov dh, dl
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pop ax
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ret
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; set up CHS data for int 13h for reading sector zero
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.zero: mov cx, 1 ; C=0, S=1
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mov dh, 0 ; H=0
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pop ax
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ret
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; ABSOLUTE DISK READ / DISK WRITE
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int25h: mov ah, 2
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jmp adisk
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int26h: mov ah, 3
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adisk: push bp
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push ds
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push es
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mov bp, sp
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cmp cx, 0xFFFF
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je .islrg
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; build a disk access packet on the stack
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push ds ; dword transfer buffer
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push bx
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push cx ; word number of sectors
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push cs ; dword starting sector number (CS always 0)
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push dx
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; set our freshly created dap as DS:BX
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mov bx, sp
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push ss
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pop ds
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.islrg: mov dl, al
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call fndchs
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call calchs
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mov dl, al
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mov al, [bx+4]
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mov es, [bx+8]
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mov bx, [bx+6]
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int 0x13
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jc .ret
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.ret: mov sp, bp
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pop es
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pop ds
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pop bp
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retf: retf
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; DOS IDLE INTERRUPT
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; Usually hooked by TSRs
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idle: sti
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@ -370,6 +192,8 @@ fputc: push ax
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pop ax
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iret
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%include "kernel/diskio.asm"
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vects: dw int20h, int21h, retf, retf
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dw retf, int25h, int26h, int20h
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dw idle, fputc
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@ -428,11 +252,4 @@ section .bss
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stack: resw stacks
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; default int 25h/26h handler use a cache to keep geometry for
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; the first 4 drives
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chstab: resw (4*chs_siz)
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bpb: resb bpb_len
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drvnum: resb 1
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align 4
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drvoff: resd 1; partition offset
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drvpos: resd 1; absolute physical sector number
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buffer: resb 512
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@ -0,0 +1,112 @@
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section .bss
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chsspt: equ 0 ; word sectors per track
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chsnos: equ 2 ; word number of sides
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chspo: equ 4 ; dword partition offset
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chssiz: equ 8
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chstab: resw (4*chssiz)
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section .text
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; Convert between drive number and BIOS dl
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; Bidirectional mapping
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; 0 <-> 0, 1 <-> 1, 2 <-> 0x80, 3 <-> 0x81
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dnconv: mov cx, 7
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ror dx, 1
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rol dl, 1
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dncl: rcl dl, 1
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rcr dh, 1
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loop dncl
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xchg dh, dl
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ret
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fndchs: ; find CHS table entry
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; IN dl DOS drive number (A=0, B=1, ...)
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; OUT cs:si ptr to chs table entry
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push ax
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mov ax, chssiz
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mul dl
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add ax, chstab
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mov si, ax
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pop ax
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ret
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; compare sector number in disk access packet with zero
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; sets zero flag accordingly
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iszero: push ax
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mov ax, [bx]
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or ax, [bx+2]
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pop ax
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ret
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; calculate CHS from dap and CHS table entry
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; IN ds:bx disk access packet
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; cs:si chstab table entry
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; OUT cx,dh chs data for int 13h
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calchs: push ax
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; load linear sector number
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mov dx, [bx+2]
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mov ax, [bx]
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; if any word of it is non-zero, we need to do calculation
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call iszero
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jz .zero
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; ax is track number (lba / spt)
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; dx is sector (lba % spt) + 1
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div word [cs:si+chsspt]
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inc dx
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; sector number
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mov cl, dl
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; ax is cylinder (track / heads)
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; dx is head (track % heads)
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xor dx, dx
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div word [cs:si+chsnos]
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; set up cylinder and head number
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mov ch, al
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mov dh, dl
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pop ax
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ret
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; set up CHS data for int 13h for reading sector zero
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.zero: mov cx, 1 ; C=0, S=1
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mov dh, 0 ; H=0
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pop ax
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ret
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; ABSOLUTE DISK READ / DISK WRITE
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int25h: mov ah, 2
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jmp adisk
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int26h: mov ah, 3
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adisk: push bp
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push ds
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push es
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mov bp, sp
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cmp cx, 0xFFFF
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je .islrg
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; build a disk access packet on the stack
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push ds ; dword transfer buffer
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push bx
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push cx ; word number of sectors
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push cs ; dword starting sector number (CS always 0)
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push dx
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; set our freshly created dap as DS:BX
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mov bx, sp
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push ss
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pop ds
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.islrg: mov dl, al
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call fndchs
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call calchs
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mov dl, al
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mov al, [bx+4]
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mov es, [bx+8]
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mov bx, [bx+6]
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int 0x13
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jc .ret
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.ret: mov sp, bp
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pop es
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pop ds
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pop bp
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retf
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