Re: [ECOS] n00b PC booting questions

[Chuck McManis <cmcmanis at mcmanis dot com>]

At 01:59 AM 2/9/2006, Nick Garnett wrote:
> The main problem with the floppy boot code is that it renders the
> floppy totally useless for any other purpose, since it overwrites all
> the blocks that would contain the MBR and filesystem boot
> sector. Doing the equivalent on a hard disk or a CompactFlash would
> also render that device useless for any other purposes.

I hear what you're saying Nick but I don't exactly agree with it. My 
disagreement comes from your assertion that the device is "useless" for any 
other purpose. There is absolutely no reason at all that my code can't 
continue to use the device as a mass storage device, with a primitive file 
system of my own design.

> Since in most embedded systems if you go to the effort of adding an
> IDE device, you want to use it for something other than booting, what
> we really require is a mechanism for booting eCos/Redboot out of a
> filesystem.
>
> And we have one: GRUB!

Yes, after poking around I saw that GRUB booting was supported (Grub Legacy 
or Grub 2.0 ?) Rhetorical question since I'm not interested in using GRUB 
if I can avoid it.

So let's back up for a minute. On my embedded system I get IDE devices "for 
free" as I'm simply leveraging an existing design rather than rolling my 
own. Further, I've got some firmware in that system, BIOS, which already 
knows how to start up programming from a device attached to the IDE bus.

I'm documentation challenged as I'm not part of the "Secret Society of PC 
Developers" so for whatever reason manufacturers are loathe to tell exactly 
how their hardware works or what it is expecting, but they do adhere to 
generally established conventions and standards. This at least allows me to 
get part of the way there.

Remember that at its heart, the disk on chip system is Flash, not disk, so 
treating it like a disk after I've booted is probably not the best idea 
(hence the plethora of flash file systems) further my system architecture 
is such that I have a "regular" disk for user data, and it will have a more 
standard file system, but the boot drive is really just for booting and 
initial software load.

Since my original email, I've created a boot sector that reads sectors 2-n 
(where 'n' is poked into the boot sector at install time) into memory using 
the int 13h call that BIOS provides. I'm currently looking at telling 
Redboot to expect "RAM" startup and making sure that place where I load it 
is where it expects to be. Is there a vector to the start address stored in 
the first address of Redboot?

--Chuck

(thanks again for the GRUB support, that is really good stuff and if the 
worst comes to pass I can use it as a workaround) 


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