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> OS Construction > Need Help with my Bootloader... |
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Plue 24 Feb 2006, 11:36
Are you sure you want the data before the instructions without any "jump past data instruction" in front of it?
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24 Feb 2006, 11:36 |
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Borsuc 24 Feb 2006, 16:29
My advice: If you don't want to jump, you MUST put all the global variables after the code, so they WON'T get executed... I would choose this method
OR, you can put a jump RIGHT BEFORE your global data (i.e the strings)... this is because the code will start executing your 'db' directives (IT WILL NOT START at start: label, 'cause labels ARE just some names that are NOT in the .exe/.bin/whatever..).. so, try something like: Code: ;============================================= ; Bootloader ;============================================= org 0x7c00 ; Bootsector Starting Read Location use16 ; Use 16-Bit Assembler Code ; OK, processor WILL EXECUTE from here... jmp start ; jump to start label ;================================= ; Defined Data and Messages ;================================= RealmodeMsg db 'Entering Realmode...' ProtectedmodeMsg db 'Entering Protected Mode...' LoadFloppyDrvMsg db 'Loading Floppy Driver...' FloppyDrvTestMsg db 'Testing Floppy Driver...' LoadMouseDrvMsg db 'Loading Mouse Driver...' MouseDrvTestMsg db 'Testing Mouse Driver...' LoadKeybMapMsg db 'Loading Keyboard Map...' LoadKeybDrvMsg db 'Loading Keyboard Driver...' KeybDrvTestMsg db 'Testing Keyboard Driver...' LoadSysLibraryMsg db 'Loading System Library...' LoadAsmLibaryMsg db 'Loading Assembly Library...' LoadCeeLibraryMsg db 'Loading C Library...' SuccessMsg db '[Done]' ;========================= ; Entering Realmode ;========================= start: ... |
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24 Feb 2006, 16:29 |
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Dex4u 24 Feb 2006, 19:54
1. you need the jmp.
2. You need a print routine like this: Code: lea esi,[ProtectedmodeMsg] mov edi,0xB8000 + 4 mov ecx,51 cld rep movsbProtectedmodeMsg db 'E n t e r i n g P r o t e c t e d M o d e . . . ' 3. Also note that, with the data at the start the Code: times 510- ($-start) db 0dw 0xaa55 |
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24 Feb 2006, 19:54 |
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Borsuc 28 Feb 2006, 17:03
1. Why do you really need the jump? It can be done without it as well...
2. Why don't use BIOS? For booting up, I think a smaller bootloader is preferred over a faster (without slow BIOS) bootloader. BTW: Nice 'manual' printing routine, I was just about trying to figure out one myself (without BIOS 'cause I want speed and flexibility). thanks  |
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28 Feb 2006, 17:03 |
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Dex4u 01 Mar 2006, 00:50
Heres why you need the jump:
Code: ;=============================================; Bootloader;=============================================org 0x7c00 ; Bootsector Starting Read Locationuse16 ; Use 16-Bit Assembler Code;=================================; Defined Data and Messages;================================= ; ***** CS:IP is pointing here ***** RealmodeMsg db 'Entering Realmode...' 
by put the jmp code, it jumps over the data, to the next code (instruction). Heres a better ver, of pmode PrintString: Code: lea esi,[ProtectedmodeMsg] ; point to string mov edi,0xB8000 + 4 ; point to screen mov ah,0x09 ; color of char call PrintString ; call function ;****some more code here ****; Print string functonPrintString: cld ;process from left to rightPrintStringLoop ; Lable for loop lodsb ;load byte from ds:esi to al or al,al ;Sets the zero flag if al = 0 jz PrintEnd ; If zero flag set, jump to end stosw ; move a word from AX to es:edi jmp PrintStringLoop ; loopPrintEnd: ret ; ret to the next instr after call; DataProtectedmodeMsg db 'Entering Protected Mode..... ', 0 NOTE: It for pmode, will need moding for realmode |
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01 Mar 2006, 00:50 |
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Borsuc 01 Mar 2006, 18:13
Dex4u wrote: There should be code here not data Why not put the 'data' AFTER the code, instead of before it... so you won't need the jmp: Code: ;============================================= ; Bootloader ;============================================= org 0x7c00 ; Bootsector Starting Read Location use16 ; Use 16-Bit Assembler Code ;================================= ; code here start: .... ; Defined Data and Messages ;================================= ; ***** CS:IP is pointing here ***** RealmodeMsg db 'Entering Realmode...' Dex4u wrote: Heres a better ver, of pmode PrintString: Cool  nice and fast routine, thx |
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01 Mar 2006, 18:13 |
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kake_zinger 02 Mar 2006, 10:10
There is no real reason for the jump like shown above since we're using Fasm (a very simple single pass assembler would not have knowledge of data coming later), but usually it is done to establish a full segment for our code partly in order to be sure about the addressing because some strange bios might use 07C0:0000 instead of 0000:7C00. You actually pointed to this in another thread yourself.
By executing jmp 07C0:start start: more here we're establishing the CS as 07C0 and getting a full 64k segment for our code whereas when loading to 0000:7C00 we only have 83FF bytes left in the segment 0000. However in practice this is needless because the first priority is to enter full 32bit mode as soon as possible unless you're doing 16bit code on purpose. |
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02 Mar 2006, 10:10 |
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Dex4u 02 Mar 2006, 19:17
Your right kake_zinger, coming from other assemblers, i alwayed assumed you needed the jmp there, but it seems you do not.
Also note, as the (start) is used for the Code: times 510- ($-start) db 0dw 0xaa55 Data before the lable, will make the file bigger than 512bytes. |
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02 Mar 2006, 19:17 |
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smiddy 03 Mar 2006, 19:43
Greets All,
My tar pence on the JMP instruction or opcode as it were is that if you intend on being compatible with FAT storage on a floppy, then it is one of the requirements written into the specification. However, if you don't intend on using FAT for your floppy as a storage arrangement, then you can jump or not jump depending on your implementation. @Dex4u, Your print string function assumes that the address within the current ES starts at physical address 0. Anyone using it will need to understand the implications of using the routine if they do change their segments and may be using 24-bit protected mode, or offset segments of memory differently. That being said, given a FLAT memory model, this works like a champ! (BTW, I am working my way back into coding between now and the 20th; Can you tell?)
-smiddy |
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03 Mar 2006, 19:43 |
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tspier2 03 Mar 2006, 23:30
Alright, I looked at the comments, and I created a new copy of it. Can someone compile it, and try booting it for me? My other computer that I used for this isn't working right now, so I can't do it.
Code: ;============================================= ; Bootloader ;============================================= use16 ; Use 16-Bit Assembler Code jmp start ;================================= ; Defined Data and Messages ;================================= RealmodeMsg db 'Entering Realmode...', 0 ProtectedmodeMsg db 'Entering Protected Mode...', 0 LoadFloppyDrvMsg db 'Loading Floppy Driver...', 0 FloppyDrvTestMsg db 'Testing Floppy Driver...', 0 LoadMouseDrvMsg db 'Loading Mouse Driver...', 0 MouseDrvTestMsg db 'Testing Mouse Driver...', 0 LoadKeybMapMsg db 'Loading Keyboard Map...', 0 LoadKeybDrvMsg db 'Loading Keyboard Driver...', 0 KeybDrvTestMsg db 'Testing Keyboard Driver...', 0 LoadSysLibraryMsg db 'Loading System Library...', 0 LoadAsmLibaryMsg db 'Loading Assembly Library...', 0 LoadCeeLibraryMsg db 'Loading C Library...', 0 SuccessMsg db '[Done]', 0 ;========================= ; Entering Realmode ;========================= start: xor ax,ax ; Initialize all the Registers mov ds,ax mov es,ax mov ss,ax mov sp,0x7c00 ; Starting Read Location mov ax, 3 ; Sets mode 0x03 int 0x10 ; Runs Interrupt 10h mov bl, 2 ; Sets Cursor on Screen mov ah, 2 mov dx, 0x0201 int 0x10 ; Runs Interrupt 10h mov bp, RealmodeMsg ; Prints the Starting Messages mov ax,0x1301 mov bx,7 mov cx,12 mov dx,0x0201 int 0x10 ; Runs Interrupt 10h ;================================= ; Setting-Up Protected Mode ;================================= cli lgdt [gdtr] mov eax,cr0 or al,0x1 mov cr0,eax jmp 0x10: protected ;=============================== ; Entering Protected Mode ;=============================== protected: use32 lea esi,[ProtectedmodeMsg] mov edi,0xB8000 + 4 mov ah,0x09 ; Color call PrintStringFunction ; Calls Function to Print the String PrintStringFunction: cld PrintStringLoop: ; Label for Loop lodsb ; Load Byte from DS:ESI to al or al,al ; Sets the Zero Flag if AL = 0 jz PrintEnd ; If Zero Flag is set, jump to end stosw ; Move a Word from AX to ES:EDI jmp PrintStringLoop PrintStringEnd: ret ;======================== ; Turns off Floppy ;======================== mov dx,3F2h mov al,0 out dx,al ;============================================== ; Loads FAT, ROOT, and Searches for File ;============================================== ; mov di,0x0050 ; Loads Root to: ; mov ax,19 ; 0x0000:0x0500 ; mov cx,14 ; call Load_Root ; Calls the function that loads ; Kernel Sectors ;======================================= ; Sets up Global Descriptor Table ;======================================= gdt: dw 0x0000, 0x0000, 0x0000, 0x0000 dw 0xFFFF, 0x0000, 0x9200, 0x00CF dw 0xFFFF, 0x0000, 0x9800, 0x00CF gdt_end: gdtr: dw gdt_end - gdt - 1 dd gdt ;============================= ; Set code to 512 Bytes ;============================= times 510- ($-start) db 0 dw 0xaa55 |
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03 Mar 2006, 23:30 |
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bubach 07 Mar 2006, 14:02
are you sure that you got enought space for all those strings? i think i counted to 360 something bytes, and all you got in total is 512.
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07 Mar 2006, 14:02 |
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Dex4u 07 Mar 2006, 17:22
Also because the start label, is after the strings, you would end up with a file 360+512 or 872 bytes in size.
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07 Mar 2006, 17:22 |
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Borsuc 07 Mar 2006, 20:05
kake_zinger: yes, you would need to jump to set correct segments, but I thought it might be needless because you already jump after you load your kernel. but sure, the FAR jump is needed, though a NEAR jump can be avoided in this situation
sorry for late post, sometimes i'm not on the NET for days (i.e not very often) |
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07 Mar 2006, 20:05 |
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