Starting linux aint much easy ?

[Winter Jörg]

> I'm not sure how far you've gotten since saturday, but it sound to me like
> you are almost there.  I have set up a system to boot Linux from a flash. 
> From your descriptions, I believe you are on the right track.  Before
> jumping to Linux at 0x1000 for .....

Not far!
    I still have seveere trouble in starting the kernel ...
    from the firmware/init/main.c I am loading a vmlinux (1.2megs,
uncompressed) image into my memory at 0x100000.

I found out that the code in head.S is at offset 0x1000 inside the
image. So I jump to 0x101000. That works. 
    I modified  the file:

kernel/head.S:   to notify me if I reached the head code:

/* this is my dummycode ... to see if kernel starts 
    	.asciz  "This is the kernel image entry point\n"   << I used
this to verify that I dont load garbage into RAM ...
    Fallback from Protected mode into Realmode, CLR PE1
    */

movl	%cr0,%eax
    	andl	$0xfffffffe,%eax
    	movl	%eax,%cr0
    	jmp	flush
    flush:
    	mov	$0x3f8,%dx	//here i give a char out to the uart
(cause I dont have anything else to talk)
    	mov	$0x59,%al
    	out	%al ,%dx

>>>>> until here everything works fine. but then ...

cld
    	movl $(__KERNEL_DS),%eax
    	movl %ax,%ds
    	movl %ax,%es
    	movl %ax,%fs
    	movl %ax,%gs
    #ifdef __SMP__
    	orw %bx,%bx
    	jz 1f

...
...
a bit later it should do: (same file)
    xorl %eax,%eax
    lldt %ax
    cld			# gcc2 wants the direction flag cleared at
all times
    call SYMBOL_NAME(start_kernel)
L6:
    jmp L6			# main should never return here, but
    			# just in case, we know what happens.

...
therefore I expected to see the message i have put in
/usr/src/linux/init/main.c : start_kernel(void)

asmlinkage void __init start_kernel(void)
{
    char * command_line;
    int  i;
#ifdef __SMP__
    static int boot_cpu = 1;
    /* "current" has been set up, we need to load it now */
    if (!boot_cpu)
    	initialize_secondary();
    boot_cpu = 0;
#endif

/*
 * Interrupts are still disabled. Do necessary setups, then
 * enable them
 say that were here already ...
 */
    outb(0x58,0x03f8); 
    for (i=0; i<0x0fff; i++);
    printk(linux_banner);

....
....

but somewhere inbetween the machine stops. I cannot see my second char on
the uart. I dont have an in-circuit debugger
and since I´m not the prophet I dont know why and where it crashes ...

Any ideas on that ??

btw. sorry for the lots of code i sent, but like that it was easier to show
where I got stuck ...

greetings, Jake.

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[Ronald G. Minnich]

I don't think you should fall back into real mode. There's no good reason
to. I think you should look at how LOBOS does its thing, which is to boot
linux entirely in protected mode, and emulate that in your bios.

Falling into real mode is a mess. Also, once you drop to real mode, you
can't address 0x100000 any more. This is probably not what you want, since
your code is at 0x101000.

ron

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