Cross Building Linux With ELLCC: Part 5 – Making an SD Card to Boot the Pi.

UPDATE: A more streamlined version of this process is available: From 0 to Raspberry Pi Linux in 45 Minutes

In previous posts I’ve described building the Linux kernel using ELLCC, building Linux for a Raspberry Pi B+, building Linux for the Pi 2, and building Linux on a Mac. In this post we’ll build enough userland and create an SD card that will boot on the Raspberry Pi 2. I just got it to boot this evening and it only gets to the login prompt where I can log in as root, but I think it is pretty cool nonetheless.

I mentioned the ellcc/libecc/ecclinux directory that is in the ELLCC source tree and is included in the ELLCC binary distributions. In this directory, there is a little script that will get sources for the Linux kernel from, and a bunch of userland programs from and other places. The script will then patch the sources if necessary and build them.

These are the steps I took to create a boot-able SD card. I happened to have a 32 Gig SD card lying around, so I decided to use it. On my Linux box, an SD card shows up as /dev/sdc* so the following commands reflect that. Your system may assign different name. You should verify the name by using df, or something similar, to determine what a newly inserted SD card is.

I’m going to go into a bit of detail here because it is the first time I did this for Linux and I want to keep a detailed record.

UPDATE: I made a little script that populates the SD card. It is in the source repository. The script replaces/enhances the rest of this post.

The first thing I did was to remove the old partitions on the card.

  sudo parted /dev/sdc print
    Model: Generic- SD/MMC (scsi)
    Disk /dev/sdc: 32.1GB
    Sector size (logical/physical): 512B/512B
    Partition Table: msdos
    Disk Flags: 

    Number  Start   End     Size    Type     File system  Flags
     1      512B    62.9MB  62.9MB  primary
     2      62.9MB  67.1MB  4209kB  primary

My card had 2 partitions that I got rid of:

  sudo parted /dev/sdc rm 1
    Information: You may need to update /etc/fstab.

  sudo parted /dev/sdc rm 2
    Information: You may need to update /etc/fstab.

  sudo parted /dev/sdc print                                       
    Model: Generic- SD/MMC (scsi)
    Disk /dev/sdc: 32.1GB
    Sector size (logical/physical): 512B/512B
    Partition Table: msdos
    Disk Flags: 

    Number  Start  End  Size  Type  File system  Flags

Now that the old partitions are gone, we can make new partitions for the Pi. The Pi boots using two partitions, one is in MS-DOS or FAT format, the other is in Linux ext4 format. The Pi has an interesting boot sequence, which is nicely described on this page, but basically the GPU starts up first and executes a first and second stage boot loader, which is really the GPU’s OS, before the ARM is brought up and the Linux kernel is booted. The FAT partition is used by the GPU and contains all the files it needs. The ext4 partition contains the rest of the Linux userland. The FAT partition os mounted as /boot after the ext4 partition is mounted as /.So the next step is to create these two partitions. First the FAT partition:

sudo parted -a optimal /dev/sdc unit chs mkpart primary 0,130,2 8,40,31
sudo parted /dev/sdc set 1 lba on

Now we can fill the rest of the disk with the ext4 partition:

sudo parted -a optimal /dev/sdc mkpart primary 67.1MB 100%

Now we’ll format the file systems:

  sudo mkfs -t fat /dev/sdc1
    mkfs.fat 3.0.27 (2014-11-12)

Then the ext4 partition:

  sudo mkfs -t ext4 /dev/sdc2
    mke2fs 1.42.12 (29-Aug-2014)
    Creating filesystem with 7820288 4k blocks and 1957888 inodes
    Filesystem UUID: 3823b7f5-66b6-4e9f-a10e-4a6658d6469f
    Superblock backups stored on blocks: 
            32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 

    Allocating group tables: done                            
    Writing inode tables: done                            
    Creating journal (32768 blocks): done
    Writing superblocks and filesystem accounting information: done   

We have to mark the first partition as the boot partition:

  sudo parted /dev/sdc set 1 lba on
    Information: You may need to update /etc/fstab.

  sudo parted /dev/sdc print
    Model: Generic- SD/MMC (scsi)
    Disk /dev/sdc: 32.1GB
    Sector size (logical/physical): 512B/512B
    Partition Table: msdos
    Disk Flags: 

    Number  Start   End     Size    Type     File system  Flags
     1      4194kB  67.1MB  62.9MB  primary  fat16        lba
     2      67.1MB  32.1GB  32.0GB  primary  ext4

Now we can populate the card. First, build everything using the script. If you run the script with no arguments, it will give you a hint about how to run it:

[~] dev% cd ellcc/libecc/ecclinux
[~/ellcc/libecc/ecclinux] dev% ./build 
usage: ./build [options] target
    -packages 'packag1 package2 ...'    Specific packages to build
    -exclude  'packag1 package2 ...'    Specific packages to exclude
    -clean                              Clean up a previous build
    help                                This message
    bcmrpi                              Raspberry Pi    (ARMv6)
    bcm2709                             Raspberry Pi 2  (ARMv7)
  available packages:
    uboot kernel sinit sbase ubase smdev nldev nlmon svc sdhcp loksh
          ntfs3g iproute2 e2fsprogs vim ellcc
  packages not buildable on the Mac:
    uboot iproute2 e2fsprogs vim

In this case I’ll build for the Raspberry Pi 2:

[~/ellcc/libecc/ecclinux] dev% ./build bcm2709
  CHK     include/config/kernel.release
  GEN     ./Makefile
  CHK     include/generated/uapi/linux/version.h
  CHK     include/generated/utsrelease.h
  Using /home/rich/ellcc/libecc/ecclinux/linux-4.1.15 as source for kernel

The SD card can be populated after the build completes:

  mkdir boot root
  sudo mount /dev/sdc1 boot
  sudo mount /dev/sdc2 root
  cp -r image/arm-linux-engeabihf/bcm2709/* boot
  sudo cp boot/vmlinuz-4.1.15-v7 boot/kernel7.img
  cd image/arm-linux-engeabihf/
  tar cvfp - bin etc lib sbin usr var | (cd ../../root; sudo tar xfp -)
  cd cm2709/
  rm -fr *.old
  tar cvfp - * | ( cd ../../../boot ; sudo tar xfp - )
  cd ../../..
  cd etc
  chmod oug+x rc.*
  cp * ../root/etc/
  cd ../sbin
  tar cvfp - * | ( cd ../root/sbin/ ; sudo tar xf - )
  cd ../bin
  chmod oug+x *
  tar cvfp - * | ( cd ../root/bin/ ; sudo tar xf - )
  sudo cp boot.rpi/* boot/
  cd root
  sudo mkdir root proc sys var/run
  sudo mknod dev/tty0 c 4 0
  cd ..
  sudo umount boot root

I popped the SD card into my Pi 2 and finally got the login: prompt. The initial root password is empty.

This has been a busy weekend. I got a boot, the Packers won, and it is late Sunday night and I have to work early tomorrow. I will be making the SD create steps into a script soon, but for now I’ll put up a new binary release of ELLCC, version 0.1.26, that has all the changes if you want to try this out.

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