[coreboot] minimum linuxbios

[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