FAQ question fixup

Stefan Reinauer stepan at openbios.org
Wed Mar 2 05:29:01 CET 2005

* Richard Smith <smithbone at gmail.com> [050302 17:00]:
> I've been adding selected info from my V1 FAQ up into the wiki.  The
> following is some info I compiled up on V1 start up.
> If someone(s) would update this for V2 and post it t the wiki I think
> it would be very useful.

I have an old writeup on this for v2 at home. I'll try to find it
(printout) I think this should even go to an extra page.

> ================================
> Help!  I'm a newbie and I'm completely lost in the code.
>    There seem to be two main parts to linuxbios. The first is 
>    arch/{arch}/config/ctr0.base which does the very low level initialization, 
>    like turning on memory, etc. The second is arch/{arch}/lib/c_start.S which 
>    does whatever else is necessary to call the C function hardwaremain(). 
>    hardwaremain() then does whatever else is necessary to load linux.
>    c_start.S is linked with linuxbios.a, a library containing generic support 
>    routines (those found in the lib directory) and anything specified using the 
>    'object'  directive in a Config file (and other stuff). The resultant 
>    'executable' is called linuxbios_c. The loader script used to link 
>    linuxbios_c is config/linuxbios_c.ld, and is configured to be
> loaded relative
>    to _RAMBASE.
>    crt0.base is not linked against anything. Any additional assembly routines 
>    you need must be specified using the 'mainboardinit' directive in a Config 
>    file. This causes the specified assembly file to be added to 
>    "crt0_includes.h" which is in turn included at the start of crt0.base (or at 
>    the end in the case of the ppc version). The loader script used to link 
>    crt0.base is in arch/{arch}/config/ldscript.base. The resultant 'executable' 
>    is called linuxbios and will be loaded at _ROMBASE. The tricky thing is that 
>    this loader script will also load the linuxbios_c 'executable' at a location 
>    called _payload in this file. The main task of crt0.base is then to 
>    initialize enough hardware so that this payload can be copied from rom into 
>    ram (which may also involve uncompressing code). Then control is transferred 
>    to _start, which is the first location in linuxbios_c.
>    To get an idea of how crt0.base works, look at the following files. This is 
>    the order of execution specified by the configuration file for sis735.
>      cpu/i386/entry16.inc
>      cpu/i386/entry32.inc
>      superio/sis/950/setup_serial.inc
>      pc80/serial.inc
>      arch/i386/lib/console.inc
>      cpu/k7/earlymtrr.inc
>      northsouthbridge/sis/735/raminit.inc
>      arch/i386/config/crt0.base
>    Next look at c_start.S which will show you what happens once control is 
>    transferred to _start. Finally, look at
> arch/{arch}/lib/hardwaremain.c to see
>    what other stuff is done to get linux loaded.
>    Most other files are specific to particular hardware, so it can be pretty 
>    confusing to just browse the tree.
> -- 
> Richard A. Smith
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