Board:tyan/s2892

Purpose

Customize the system to allow me to play with memory mappings and large devices. I wanted to minimize intermediate steps from LinuxBIOS to Linux to minimize the areas of expertise I needed to develop. I also wanted to be able to use the SATA drives as my boot drives.

Disclaimer

There are several places where my solutions are not as elegant as I wished them to be. Suggestions are welcome.

Current set up

• Tyan s2892
• LinuxBIOS with Linux 2.6.18-tiny as a payload

The procedure

I started by installing LinuxBIOS on the system and using FILO and Etherboot to boot to a kernel. This allowed me to try the different payloads without flashing every time.

Next I downloaded the OLPC buildrom

git clone git://dev.laptop.org/users/jcrouse/buildrom

I modified the Config.mk to include pciutils from

http://buildroot.uclibc.org/cgi-bin/viewcvs.cgi/trunk/buildroot/package/

and took out the graphical boot menu. I also modified buildrom/skeleton/devices.txt to add lines for my hard drives. I just copied the lines for sda and sda1 and made hda hda1 hda2 and sda2. The important thing is to make sure that the major and minor numbers are correct.

I modified buildrom/skeleton/linuxrc so that the device files were created earlier, /dev/null didn't become a text file, and my drives got mounted in read-only mode.

I then modified buildrom/skeleton/bin/boot.functions so that doboot() called my script on the hard drive for the kexec. That's nice to avoid flashing the BIOS for booting different kernels.

I downloaded Linux 2.6.18.1 (2.6.18-rc4 had some problems with SATA) and patched it with the tiny patches that came with OLPC. 12-tiny-tiny-crc.patch fails, but was easy to apply by hand.

I configured the kernel to include support for ext2, SATA, and IDE.

I ran make and copied the payloads from the buildrom/deploy directory to my s2892 to be used. olpc-payload.elf.lzma (732K) is used for booting directly from LinuxBIOS, and olpc-payload-uncompressed.elf (1.7M) was useful for testing it with FILO and Etherboot.

mkelfImage wouldn't work with the vmlinux file, so I changed the Makefile to get it to use the bzImage instead.

Now I have

• fallback/linuxbios.strip (88K)
• normal/payload (860K)
• s2892vBIOS.bin (36K)

WARNING: I have a bios savior so that when I mess up I can get my machine back. If you don't have one, you might not want to do the fallback only boot.

Config.lb

# Sample config file for
# the Tyan s2892
# This will make a target directory of ./s2892

target s2892
mainboard tyan/s2892

option ROM_SIZE      = 0xf7000 # 8Mbit - 36K for VGA BIOS

option CONFIG_ROM_STREAM=1

option CONFIG_CONSOLE_SERIAL8250 = 1
option CONFIG_CONSOLE_VGA = 1
option FALLBACK_SIZE = ROM_SIZE
option ROM_IMAGE_SIZE = 0x16000

# Tyan s2892
romimage "fallback"
        option CONFIG_COMPRESSED_ROM_STREAM_LZMA=1
        option CONFIG_PRECOMPRESSED_ROM_STREAM=1
        option USE_FALLBACK_IMAGE=1
        option LINUXBIOS_EXTRA_VERSION="$(shell cat ../../VERSION)_Fallback"
        payload ../olpc-payload.elf.lzma
end

buildrom ./linuxbios.rom ROM_SIZE "fallback"

Kexec-tools

Because the kexec tools that are included with OLPC's buildrom are stripped down for 32-bit kernels, I built kexec statically linked (read "large file") and put it on the hard drive with the kernel to be loaded. I use kexec to boot my kernel which has been combined with initrd into an elf with mkelfImage:

mkelfImage --comand--line="ro root=/dev/hda1 console=tty0" --kernel="" --initrd="" --output="mylinux.elf"

I have to use

kexec -f mylinux.elf 

because otherwise kexec calls shutdown and there is no shutdown in the OLPC initrd. I guess that's a half truth, because when I call kexec without the -f it reboots the machine completely instead of a kexec when shutdown is available.

Status

My machine boots LinuxBIOS, then linux-2.6.18.1-tiny, then kexecs into linux-2.6.18.1-normal. It takes a little longer than going through elfboot and FILO, but it is a simpler path.

Author

This document was written by Myles Watson <myles at pel dot cs dot byu dot edu>