minimum linuxbios

[Masoud Fatollahy]

Hi,

I am working to make a minimal linuxbios without any payload or linux 
kernel, I just want to see a nice hello word string on the serial port and 
nothing else. is it possible to make such a bios? also to setup only the 
necessary HW registers and memory to see the printout message.

how should i do this?

thanks,

/Masoud

[Mark Marshall]

Masoud Fatollahy wrote:
> Hi,
>
> I am working to make a minimal linuxbios without any payload or linux 
> kernel, I just want to see a nice hello word string on the serial port 
> and nothing else. is it possible to make such a bios? also to setup only 
> the necessary HW registers and memory to see the printout message.
>
> how should i do this?

Look at SerialICE:

http://www.serialice.com/News/News.html

This is a mini monitor that runs over the serial port.  The coreboot
developers use it to step through a BIOS image, but it contains
just enough to get the serial port working.  Memory is not
initialized, so everything is done with registers.

MarkM

[Peter Stuge]

Hej Masoud,

Masoud Fatollahy wrote:
> I am working to make a minimal linuxbios

Note that LinuxBIOS is not really used anymore. The project changed
it's name to coreboot.
> without any payload or linux kernel,

..and *if* LinuxBIOS *is* used, then it refers to coreboot+Linux
kernel as payload.

That said, if you want to control what happens with the system after
coreboot, then you need a payload.
> I just want to see a nice hello word string on the serial port and
> nothing else.

Then you need to disable all debugging in coreboot, it will otherwise
send a bunch of messages over the serial port. And you will also need
to make a minimal payload using libpayload. It will look like:

#include <libpayload.h> /* reservation: you may need other headers */

int main() {
  printf("Hello, world!\n");
  while(1);
}

That is then compiled with lpgcc -o hello.elf hello.c and you'll use
hello.elf as payload. It's very simple.
> is it possible to make such a bios? also to setup only the 
> necessary HW registers and memory to see the printout message.

coreboot does complete init of the components in the system which it
knows about from compile time, and which it finds during system
enumeration at run time.

My guess is that your concern is boot speed rather than lines of code
actually used. On smaller systems coreboot typically runs in a few
hundred milliseconds. If that's not enough, then yes, you'll have
some work to do in order to minimize the code being executed.
> how should i do this?

Get a supported hardware and start experimenting. You can do some
testing with QEMU also.

//Peter