Booting from a SD card

[nonrepe...@gmail.com]

I've been banging my head against a boot problem for a couple of days and have come to the conclusion that I need to ask someone.

Background: I have a bunch of BeagleBone Black Rev C boards. I want to load Gentoo onto a SD card. I used the "beaglebone black" SD creator script to do so, but pretty quickly came to realize that the script was making an "old style" SD image with a small VFAT partition and a ext4 partition. Looking at a current beaglebone SD image (which does boot just fine), I found the link to a page that explains how to create an image. So, I created an image using this script that I threw together based upon the instructions:

#!/bin/bash

# some useful variables

SCRIPTNAME=$(echo $0 | sed 's|^.*/||g')

DEVICE=""

MLOFILE=""

UBOOTIMAGE=""

ROOTFS=""

# text parsing WON'T WORK unless it is in english

export LC_ALL=C

# make sure there are enough options

if [ $# != 4 ]

then

    echo "Usage:"

    echo "  $SCRIPTNAME <device> <MLO> <u-boot.img> <rootfs tar.gz >"

    echo "  Example: $SCRIPTNAME /dev/sdc MLO u-boot.img nfs.tar.gz"

    exit

fi

# make sure the options are valid

if [[ -e $1 ]]

then

    DEVICE=$1

else

    echo "Invalid device!"

    exit

fi

if [[ -e $2 ]]

then

    MLOFILE=$2

else

    echo "Incorrect MLO location!"

    exit

fi

if [[ -e $3 ]]

then

    UBOOTIMAGE=$3

else

    echo "Incorrect u-boot.img location!"

    exit

fi

if [[ -e $4 ]]

then

    ROOTFS=$4

else

    echo "Incorrect rootfs location!"

    exit

fi

# prompt for total destruction

echo "All data on "$1" now will be destroyed! Continue? [y/n]"

read ans

if ! [ $ans == 'y' ]

then

    exit

fi

echo "[ clearing sectors...]"

dd if=/dev/zero of=$DEVICE bs=1M count=1

DISKSIZE=`fdisk -l $DRIVE | grep Disk | awk '{print $5}'`

echo "  DISK SIZE: $DISKSIZE bytes"

echo

echo "[ writing MLO...]"

dd if=$MLOFILE of=$DEVICE count=1 seek=1 conv=notrunc bs=128K

echo "[ writing u-boot image...]"

dd if=$UBOOTIMAGE of=$DEVICE count=2 seek=1 conv=notrunc bs=384K

echo "[ creating root partition...]"

PARTITIONOFFSET=$(echo 384*1024*3 | bc)

echo $PARTITIONOFFSET,,0x83,- | sfdisk $DEVICE

echo "[ creating filesystem...]"

mkfs.ext4 -L rootfs -T small "$DEVICE"1 &> /dev/null

echo "[ copying files...]"

if ! [ -e /mnt/sdcard ]

then

    mkdir /mnt/sdcard

    if [ $? != 0 ]

    then

echo "failed to create mountpoint!"

exit

    fi

fi

mount "$DEVICE"1 /mnt/sdcard

if [ $? != 0 ]

then

    echo "failed to mount filesystem!"

    exit

fi

tar zxvf $ROOTFS -C /mnt/sdcard

chmod 755 /mnt/sdcard

umount "$DEVICE"1

echo "[Done]"

My image does not boot. There seem to be two issues:

1) Watching the serial console during boot, I see "U-Boot SPL 2015.10-00001-g143c9ee (Nov 06 2015 - 15:27:19)

bad magic". Looking on this site, it seems like the U-Boot SPL should be picking up the MLO that I wrote to my disc and boot my new u-boot image, right? What would cause "bad magic"?

2) When I interrupt u-boot and try to take a look at my ext4 partition, I see the following:

=> ext4ls mmc 0:1 /boot 

<DIR>       1024 .

<DIR>    3145753 ..

             102 fsf-funding.7

              11 gpl.7

           11619 gfdl.7

Even if the problem mentioned in #1, above, happens, the default u-boot should be able to boot my kernel as the directory mmc 0:1 /boot is populated with:

$ ls -la

total 10122

drwxrwxrwx  3 root root    1024 Jun  5 14:05 .

drwxrwxrwx 20 root root    1024 Jun  5 14:31 ..

-rw-rw-rw-  1 root root   87161 Jun  2 14:11 am335x-boneblack.dtb

-rw-rw-rw-  1 root root  126411 Jun  2 14:12 .config

-rw-rw-rw-  1 root root     492 Jun  2 14:25 SOC.sh

-rw-rw-rw-  1 root root 2969405 Jun  2 14:11 System.map

drwxrwxrwx  2 root root    1024 May 31 12:56 uboot

-rw-rw-rw-  1 root root     405 Jun  5 14:05 uEnv.txt

-rwxrwxrwx  1 root root 7175152 Jun  2 14:10 vmlinuz-3.14.79

That's what I see on my host system. u-boot seems to be listing files present in /usr/share/gcc-data/armv7a-hardfloat-linux-gnueabi/4.9.4/man/man7 rather than what is present in /boot. That would seem to indicate that u-boot is not reading the ext4 filesystem correctly. Is there some magic that needs to be present in an ext4 filesystem in order for u-boot to read it correctly? I tried shrinking my partition size down to 3.6GB to match the beaglebone SD image, but that had no effect. I didn't see anything about directory depth limits nor about size limits, but clearly something is not working properly.

Any answers or pointers to better (correct) documentation are greatly appreciated.