Index
> OS Construction > floppy sector os issues |
| Author |
|
|
mkriegel 28 Jul 2007, 15:45
Hi Gizmo,
some ideas: 1. use jmp far 0x800:0x0 doing so will setup the cs-register with 0x800. -> 2. set the ds, es, fs and gs-registers if nessesary: mov ax, cs mov ds, ax mov es, ax ... 3. post some code to the forum BYE MK |
|||
28 Jul 2007, 15:45 |
|
|
Gizmo 29 Jul 2007, 09:14
Those directives are only for the integrated emulator so you can debug/emulate the sector 2 program without first running sector 1.
It sets the cpu registers to how the bootsector program leaves them after it jumps to sector 2. I found my problem... My stack was not set up correctly, so that when i did push strHello call PrintString16 it was outputting garbage because the stack was overwriting my data because thats where the stack was initially. I set the stack up to use the same stack space of the bootsector program and now it works fine. In case your confused: sector 1: bootsector that loads kernel from sector2+ and jumps to it sector 2+: the kernel that outputs string "hello from kernel" I needed the extra space provided by using more than 1 sector because my bootsecotr 512 byte pmode task switching project ran out of space when I tried to implement an interupt table. I could use a file system, but I just don't feel like it I guess. I wonder if in fat12 you can hide the last couple of sectors and stash an os in there? (similar to how the windows scandisk marks sectors as bad and unusable) |
|||
|
29 Jul 2007, 09:14 |
|
|
Mac2004 29 Jul 2007, 09:41
Gizmo: Perhaps my boot sector example that loads a binary secondary file will help you a bit.
Here's the link: http://board.flatassembler.net/topic.php?t=6529 regards, Mac2004 |
|||
|
29 Jul 2007, 09:41 |
|
|
Gizmo 30 Jul 2007, 15:50
I got everything else to work, now I cant get my idt to work.
When I call an interrupt it crashes, but as long as I dont use them it run fine. I read through all of the tutorials I could find and read the intel manual a few more times but I still don't see anything wrong. Here is the code in question: (remember its loaded at 8000h or 800h:0 in real mode) Code: org 0h jmp BOOT_ENTRY ;used by bootsector to check first byte to make sure it was loaded correctly ;---------------------------------16 bit entry --------------------------------------------------------------------------------- use16 BOOT_ENTRY: ; initialize the stack: mov ax, 07c0h mov ss, ax mov sp, 03feh ; top of the stack. ; set data segment: mov ax, 800h mov ds, ax ;enable the a20 memory gate to access above 1 meg of ram call Enable_A20 ;disable interupts cli ;load the GDT (gloabl description table) descriptor lgdt [ds:gdt_32_desc] ;load interupt descriptor table lidt [ds:idt_32_desc] ;set bit 0 of cr0 to 1 enabling protected mode mov eax, cr0 or eax, 1 mov cr0, eax ;jump to 32 bit code segment to clear out instruction cache jmp 08h:PMODE_ENTRY+8000h ;---------------------------------32 bit entry --------------------------------------------------------------------------------- use32 PMODE_ENTRY: ;set ds(data segment) and ss(stack segment) register to data segment identifier mov ax, 10h mov ds, ax mov ss, ax mov esp, 090000h ; Move the stack pointer to 090000h ;continuously draw a random charactor hang: mov ebx, 0B8000h inc byte [ds:ebx] inc ebx inc byte [ds:ebx] ;use interupt 32 (0x20) ; int 20h jmp hang ;---------------------------------16 bit enables a20 memory gate ------------------------------------------------------------------ ;; ;; enableA20.s (adapted from Visopsys OS-loader) ;; ;; Copyright (c) 2000, J. Andrew McLaughlin ;; You're free to use this code in any manner you like, as long as this ;; notice is included (and you give credit where it is due), and as long ;; as you understand and accept that it comes with NO WARRANTY OF ANY KIND. ;; Contact me at jamesamc@yahoo.com about any bugs or problems. ;; use16 Enable_A20: ;store all registers pusha ;disable interupts cli ;5 attempts to enable a20 line mov CX, 5 ;first method of enabling a20 .startAttempt1: ; Wait for the controller to be ready for a command .commandWait1: xor AX, AX in AL, 64h bt AX, 1 jc .commandWait1 ; Tell the controller we want to read the current status. ; Send the command D0h: read output port. mov AL, 0D0h out 64h, AL ;Wait for the controller to be ready with a byte of data .dataWait1: xor AX, AX in AL, 64h bt AX, 0 jnc .dataWait1 ; Read the current port status from port 60h xor AX, AX in AL, 60h ; Save the current value of AX push AX ; Wait for the controller to be ready for a command .commandWait2: in AL, 64h bt AX, 1 jc .commandWait2 ; Tell the controller we want to write the status byte again mov AL, 0D1h out 64h, AL ; Wait for the controller to be ready for the data .commandWait3: xor AX, AX in AL, 64h bt AX, 1 jc .commandWait3 ; Write the new value to port 60h. Remember we saved the old value on the stack pop AX ; Turn on the A20 enable bit or AL, 00000010b out 60h, AL ; Finally, we will attempt to read back the A20 status to ensure it was enabled ; Wait for the controller to be ready for a command .commandWait4: xor AX, AX in AL, 64h bt AX, 1 jc .commandWait4 ; Send the command D0h: read output port. mov AL, 0D0h out 64h, AL ; Wait for the controller to be ready with a byte of data .dataWait2: xor AX, AX in AL, 64h bt AX, 0 jnc .dataWait2 ; Read the current port status from port 60h xor AX, AX in AL, 60h ; Is A20 enabled? bt AX, 1 ; Check the result. If carry is on, A20 is on. jc Enable_A20_success ; If the counter value in CX has not reached zero, we will retry loop .startAttempt1 ;method 2 for chipsets that don't support method 1 mov CX, 5 .startAttempt2: ; Wait for the keyboard to be ready for another command .commandWait6: xor AX, AX in AL, 64h bt AX, 1 jc .commandWait6 ; Tell the controller we want to turn on A20 mov AL, 0DFh out 64h, AL ; Again, we will attempt to read back the A20 status to ensure it was enabled. ; Wait for the controller to be ready for a command .commandWait7: xor AX, AX in AL, 64h bt AX, 1 jc .commandWait7 ; Send the command D0h: read output port. mov AL, 0D0h out 64h, AL ; Wait for the controller to be ready with a byte of data .dataWait3: xor AX, AX in AL, 64h bt AX, 0 jnc .dataWait3 ; Read the current port status from port 60h xor AX, AX in AL, 60h ; Is A20 enabled? bt AX, 1 jc Enable_A20_success ; If the counter value in CX has not reached zero, we will retry loop .startAttempt2 ;unable to enable a20 Enable_A20_fail: sti popa mov EAX, -1 ret ;enabled a20 Enable_A20_success: sti popa xor EAX, EAX ret ;interupt 32 0x20 handler use32 INT_HANDLER_0x20: ;save registers push ds push es pusha ;set the correct ds mov ax, 10h mov ds, ax mov es, ax ;draw random charactor at colum 2 mov ebx, 0B8002h inc byte [ds:ebx] inc ebx inc byte [ds:ebx] ;restore all registers popa pop es pop ds ;return from interupt iret ;--- 32 bit global segment descriptor table----------------------------------------------------- gdt_32: ;gdt entry format ;byte #7 ;63 - 56 Upper Byte of Base Address ;55 Granularity Bit ;54 Default Bit ;byte #6 ;53 long mode code segment ;52 Available for Use (free bit) ;51 - 48 Upper Digit of Limit ;byte #5 ;47 Segment Present Bit ;46 - 45 Descriptor Privilege Level ;44 System Bit ;43 Data/Code Bit ;42 Conforming Bit ;41 Readable bit ;40 Accessed bit ;byte #4 ;39 - 32 Third Byte of Base Address ;byte #3 ;31 - 24 Second Byte of Base Address ;byte #2 ;23 - 16 First Byte of Base Address ;byte #1 ;15 - 8 Second Byte of Limit ;byte #0 ;7 - 0 First Byte of Limit ;null segment gdt_32_null: dd 0 dd 0 ; Code segment, read/execute, nonconforming gdt_32_code: ;limit = 16mb 1111 1111 1111 1111 1111 1111 ;address limit bytes #1 & 2 db 11111111b db 11111111b ;base = 0mb ;base address 3 byte low db 0 db 0 db 0 ;accessed=0,readable=1,conforming=0,data/code=1,system=1,priveledge=00,present=1 ;p.pp.s.d.c.r.a db 10011010b ;free=0,long seg=0,default=1,granularity=1 ;g.d.l.f + 4 bits upper of limit db 11001111b ;base address byte #4 db 0 gdt_32_code_end: ; Data segment, read/write, expand down gdt_32_data: ;limit = 16mb 1111 1111 1111 1111 1111 1111 ;address limit bytes #1 & 2 db 11111111b db 11111111b ;base = 0mb ;base address bytes #1, 2 & 3 db 0 db 0 db 0 ;accessed=0,readable=1,conforming=0,data/code=0,system=1,priveledge=00,present=1 ;p.pp.s.d.c.r.a db 10010010b ;free=0,long seg=0,default=1,granularity=1 ;g.d.l.f + 4 bits upper of limit db 11001111b ;base address byte #4 db 0 gdt_32_data_end: ;end of gdt gdt_32_end: ;--- 32 bit gdt descriptor -------------------------------------------------------- gdt_32_desc: ;size (limit) of gdt dw gdt_32_end - gdt_32 - 1 ;address of gdt dd gdt_32+8000h ;--- 32 bit interupt descriptor table -------------------------------------------------------- idt_32: ;idt entry format ;57-63 offset bytes 3 and 4 ;byte 6 ;56 present bit ;44-45 descriptor privledge level ;43 0 ;42 gate size 1=32bit, 0=16 ;39-41 110 int gate type ;byte 5 ;36-38 unused 3 bits ;32-36 reserved 5 bits ;byte 4 ;16-31 segment selector 2 bytes ;byte 2 ;0-15 offset byte 1 and 2 ;byte 0 ;first 32 interupts repeat 20h dw 0x0000 dw 0x08 dw 0xE00 dw 0x00 end repeat ;interupt 32 0x20 idt_32_int0x20: ;low offset dw INT_HANDLER_0x20 ;segment selector dw 0x08 ;reserved and unused db 0 ;type=110,size=1,unused,dpl=0,present=1 ;p.dp.0.s.typ db 10001110b ;high offset dw (INT_HANDLER_0x20+8000h)/7FFFh idt_32_end: ;--- 32 bit idt descriptor -------------------------------------------------------- idt_32_desc: ;size (limit) of gdt dw idt_32_end - idt_32 - 1 ;address of gdt dd idt_32+8000h This is the bootloader- there isnt anything wrong with it, but someone may ask to see it Code: ; boot record is loaded at 0000:7c00 org 7c00h ; initialize the stack: mov ax, 07c0h mov ss, ax mov sp, 03feh ; top of the stack. ; set data segment: xor ax, ax mov ds, ax ; print welcome message: mov si, msg call print_string ;=================================== ; load the kernel at 0800h:0000h ; 10 sectors starting at: ; cylinder: 0 ; sector: 2 ; head: 0 ; BIOS passes drive number in dl, ; so it's not changed: mov ah, 02h ; read function. mov al, 10 ; sectors to read. mov ch, 0 ; cylinder. mov cl, 2 ; sector. mov dh, 0 ; head. ; dl not changed! - drive number. ; es:bx points to receiving ; data buffer: mov bx, 0800h mov es, bx mov bx, 0 ; read! int 13h ;=================================== ; integrity check: push ds mov ax, 800h mov ds, ax cmp byte [ds:0],0EBh ; first byte of kernel must be 0E9 (jmp). pop ds je integrity_check_ok ; integrity check error mov si, err call print_string ; wait for any key... mov ah, 0 int 16h ; store magic value at 0040h:0072h: ; 0000h - cold boot. ; 1234h - warm boot. mov ax, 0040h mov ds, ax mov word [ds:0072h], 0000h ; cold boot. jmp 0ffffh:0000h ; reboot! ;=================================== integrity_check_ok: ; pass control to kernel: jmp 0800h:0000h ;=========================================== print_string: push ax ; store registers... push si ; next_char: mov al, [si] cmp al, 0 jz printed inc si mov ah, 0eh ; teletype function. int 10h jmp next_char printed: pop si ; re-store registers... pop ax ; ret ;==== data section ===================== msg db "Loading...",0Dh,0Ah, 0 err db "invalid data at sector: 2, cylinder: 0, head: 0 - integrity check failed.", 0Dh,0Ah db "System will reboot now. Press any key...", 0 ;====================================== ;-- fill up file with zeroes 512 bytes - boot sector id--------------------------- times 510-($-$$) db 0 ;--boot sector identifier--------------------------------------------------------- dw 0AA55h END_PROG: If you can see whats broke I would greatly appreciate it  |
|||
|
30 Jul 2007, 15:50 |
|
|
Gizmo 30 Jul 2007, 16:16
You have to uncomment the int 20h line so you will see it crash, if you run it as is it will run fine.
It never reaches the handler, so it is probbably something wrong with the address of the handler in the idt or the idt itself? How do you use the preprocessor to and numbers and to do bitshifts? so i can clean up this: Code: ... idt_32_int0x20: ;low offset dw INT_HANDLER_0x20+8000h ;this needs to be and'ed with FFFF ;segment selector dw 0x08 ;reserved and unused db 0 ;type=110,size=1,unused,dpl=0,present=1 ;p.dp.0.s.typ db 10001110b ;high offset dw (INT_HANDLER_0x20+8000h)/7FFFh ;bitshifted by 16 bits idt_32_end: |
|||
|
30 Jul 2007, 16:16 |
|
|
Gizmo 31 Jul 2007, 14:24
I fixed it, but its not a permanent fix
I replaced the above idt entry with Code: idt_32_int0x20: ;low offset dw INT_HANDLER_0x20+8000h ;segment selector dw 0x08 ;reserved and unused db 0 ;type=110,size=1,unused,dpl=0,present=1 ;p.dp.0.s.typ db 10001110b ;high offset dw 0 since I don't know how to use the fasm dirrectives for anding and bitshifts . It only works until my address exceedes 16 bits then I'll have issues. If anyone can tell me the directives for anding and bitshifts I would appreciate it. btw: why the heck do they have the address split up like that? why not just simply put the low and high parts together- is it for compatibility with 16 bit i286 idt's? |
|||
|
31 Jul 2007, 14:24 |
|
< Last Thread | Next Thread > |
Forum Rules:
|