flat assembler
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PCI for ATA device ? How i detect connected devices number ? (with protected mode)?
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10 Mar 2018, 13:27 |
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Fulgurance wrote: PCI for ATA device ? How i detect connected devices number ? (with protected mode)? There’s plenty of specifications available at wiki.osdev.org, but, please, trust me, your experience seems to be too low to think about it right now. Maybe you’d better spend some time using good old BIOS services before you’re ready to switch to protected mode and do all the stuff directly. |
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10 Mar 2018, 19:11 |
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Yes, i'm not pro. I take information for learn more about OS dev. But i learn quickly
But i just would like to program, i don't would like to use any interrupt. And if i would like to use my small OS on virtualbox, how i program graphic driver for virtualbox. Is there tutoriel ? |
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12 Mar 2018, 21:43 |
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Fulgurance wrote: Yes, i'm not pro. I take information for learn more about OS dev. But i learn quickly The tutorial is the graphics card specification. Again, wiki.osdev.org has some of them (AFAIR, for the most common emulated video card as well). But if you manage to write such a driver for, say, Intel HD Graphics or nVidia that would provide all or most of the capabilities, that would be a great work. Seriously, no need to stick to direct hardware progamming. The whole purpose of drivers (for OSDev) is to let you implement something in an easy way to make your OS just work for now, and later you can replace the implementation in a driver-by-driver manner. |
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13 Mar 2018, 09:09 |
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Okay, i understand, thanks for your patience and your help.
I have just last question, it's about my little test code to switch to protected mode. When i use it in Virtualbox, virtualbox have an error and close, ONLY when i switch to protected mode. Do i have an error ? Code: use16 org 0x0 mov ax,0x7C0 mov ds,ax mov es,ax mov ax,0x8000 mov ss,ax mov sp,0xf000 mov ax, gdtend mov bx, gdt sub ax, bx mov word [gdtptr], ax xor eax, eax xor ebx, ebx mov ax, ds mov ecx, eax shl ecx, 4 mov bx, gdt add ecx, ebx mov dword [gdtptr+2], ecx cli lgdt [gdtptr] mov eax, cr0 or ax, 1 mov cr0, eax jmp next next: mov ax, 0x10 mov ds, ax mov fs, ax mov gs, ax mov es, ax mov ss, ax mov esp, 0x9F000 gdt: db 0, 0, 0, 0, 0, 0, 0, 0 gdt_cs: db 0xFF, 0xFF, 0x0, 0x0, 0x0, 10011011b, 11011111b, 0x0 gdt_ds: db 0xFF, 0xFF, 0x0, 0x0, 0x0, 10010011b, 11011111b, 0x0 gdtend: gdtptr: dw 0 dd 0 times 510-($-$$) db 0x90 dw 0xAA55 EDIT: I have found, problem is org directive. I don't understand very well, what do exactly org directive; it's not about adressing? But what adress ? RAM ?[/b] Is it possible to emulate specific GPU ? For example Intel 965 HD graphic card ? (it's free software) |
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13 Mar 2018, 20:56 |
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Fulgurance wrote: Okay, i understand, thanks for your patience and your help. What made you think the problem is with org? From what I can tell, the main problem is that your code continues to run after setting up segments and stack and thus runs data as code. Assembler is a program that translates your program line-by-line into a sequence of bytes. There’s an internal counter that is used to find exact values for labels. Each time assembler generates a byte this counter is incremented by 1. By default, the initial value for the counter is 0. org is like “please, set your counter’s value to this one”. That’s why I’m pretty sure org cannot be your problem since it does effectively nothing in your program. |
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14 Mar 2018, 09:41 |
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Oh yes... it's just that ... okay, sorry, i'm really stupid ...
If i understand very well, org directive is just for add "virtual" adress, just for calculate adress interval for compiler ? And i have little question, after enter protected, why assembly example do Code: jmp dword 0x8:0x1000 I understand is necessary to jump to kernel, but why 0x8 ? I don't understand very well... |
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14 Mar 2018, 15:39 |
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Fulgurance wrote: Oh yes... it's just that ... okay, sorry, i'm really stupid ... The word “virtual” is what makes me a bit nervous since there’s a virtual directive in FASM. But, yes, in a sense that’s what org is for. In fact it is expected to be used to simplify coding: whenever you start a new block that is supposed to be loaded at some point in memory you just prependit with the offset of that point and have no need to think of anything else, the rest (address calculation for labels) is done by assembler. As for your question about 0x8, I’ll just give you a hint: take a closer look at your GDT. |
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14 Mar 2018, 20:43 |
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Fulgurance wrote: I understand is necessary to jump to kernel, but why 0x8 ? I don't understand very well... It explicitly uses the CS of the recently-loaded GDT. CS points to the second descriptor: the first one (0-7) being the "null descriptor", the second one, CS, starts at 8. Say you decide to have 2 descriptors for real-mode CS and DS and 2 descriptors for protected-mode CS and DS, you'd be using 0x18 (24) instead of 8. |
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14 Mar 2018, 20:44 |
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ManOfSteel wrote:
I’ll make a few corrections here. First, the “uses the CS of the recently-loaded GDT” part here means “loads the selector 0x8 into CS which is the segment #1 (zero-based index) in the recently-loaded GDT”. The reason it is 0x8 is in the internal format of a protected-mode segment selector (see Intel SDM). Second, let me note that for the rest of ManOfSteel’s post CS and DS should be read as “code segment” and “data segment”, not as segment register names. Third, if my memory serves me, there’re no requirements about the order of segment descriptors in GDT/LDTs, so the actual index of a segment would only be 0x18 if the number and order of segment declarations is exactly as described in the example. |
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14 Mar 2018, 21:10 |
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Okay, i understand, thanks
Just one question, how is it possible on protected mode to load kernel on RAM without interrupt ? |
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15 Mar 2018, 14:42 |
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Fulgurance wrote: Okay, i understand, thanks The question has already been answered. Nothing changes with protected mode except the addressing scheme and a few things not related to interrupts/no interrupts question. |
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15 Mar 2018, 15:16 |
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Okay sorry.
I have problem. I have made mbr with on second sector simple main loop code, but i fail to load it. What i don't understand ? (I have crash on virtualbox) Look: Code: use16 org 0x0 mov ax,0x7C0 mov ds,ax mov es,ax mov ax,0x8000 mov ss,ax mov sp,0xf000 cli lgdt [gdt] mov eax,cr0 or ax,0x1 mov cr0,eax jmp protected_mode protected_mode: mov ax,0x10 mov ds,ax mov es,ax mov fs,ax mov gs,ax mov ss,ax mov esp,0x9f000 jmp dword 0x8:start gdt_begin: db 0,0,0,0,0,0,0,0 gdt_cs: db 0xFF, 0xFF, 0x0, 0x0, 0x0, 10011011b, 11011111b, 0x0 gdt_ds: db 0xFF, 0xFF, 0x0, 0x0, 0x0, 10010011b, 11011111b, 0x0 gdt_end: gdt: dw gdt_end-gdt_begin dd gdt_begin times 510-($-$$) db 0x90 dw 0xAA55 use32 start: main: jmp main times 2048-($-$$) db 0x90 I don't understand when i turn to protected mode how to jump into my kernel on second sector... Can you give me explications ? I think i don't understant something. |
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16 Mar 2018, 16:27 |
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Fulgurance wrote: I don't understand when i turn to protected mode how to jump into my kernel on second sector... Can you give me explications ? I think i don't understant something. Only the first 512 bytes are read into memory by BIOS. So your second sector is not in memory until you load it from disk. |
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16 Mar 2018, 19:50 |
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Oh okay . I have again to learn many things
Thanks for your patience and your help. I mark this post solved  |
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16 Mar 2018, 20:42 |
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