AM335x

Prepare card

To make sure everything will run without problem wipe all data on the MMC:

$ sudo dd if=/dev/zero of=/dev/sdx bs=1k count=1024

Format the disk:

$ sudo fdisk /dev/sdx << __EOF__
> n
> 
> 
> 
> 
> w
> __EOF__

Make ext4 filesystem

$ sudo mkfs.ext4 -F -O ^metadata_csum,^64bit /dev/sdx1

NOTE: You MUST replace /dev/sdx with your device, e.g. /dev/sdc.

Cross compiler

This tutorial gcc 5.4.0 is used:

$ arm-linux-gnueabihf-gcc --version
arm-linux-gnueabihf-gcc (Debian 5.4.0-6) 5.4.0 20160609
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE

On Ubutuntu/Debian run:

$ sudo apt-get install gcc-5-arm-linux-gnueabihf

Optionally download toolchain from here. For example:

$ wget https://releases.linaro.org/components/toolchain/binaries/latest-5/arm-linux-gnueabihf/gcc-linaro-5.3.1-2016.05-x86_64_arm-linux-gnueabihf.tar.xz
$ tar -xf gcc-linaro-5.3.1-2016.05-x86_64_arm-linux-gnueabihf.tar.xz -C /opt

Then export to PATH:

$ expot PATH=$PATH:/opt/gcc-linaro-5.3.1-2016.05-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/bin/

U-Boot

Building U-Boot

Get sources:

$ git clone git://git.denx.de/u-boot.git
$ cd u-boot

The patch is built against specific commit, so reset repository:

$ git reset --hard b89dfcfd926b8224edd24608065eb9bb601c0d3b

Get and apply patch:

$ wget <patch name>
$ git apply <patch name>

Build image, where <board_defconfig> is am335x_olimex_som_defconfig or am335x_olimex_som_nandboot_defconfig:

$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- <board_defconfig>

This will produce two files:

• MLO
• u-boot.img

Writing U-Boot

Writing to MMC

Insert your card and write MLO and u-boot.img:

$ sudo dd if=MLO of=/dev/sdx count=1 seek=1 bs=128k
$ sudo dd if=u-boot.img of=/dev/sdx count=2 seek=1 bs=384k 

Kernel

We are going to use kernel 4.4 from TI.

Getting the sources

Clone into repository:

$ git clone git://git.ti.com/ti-linux-kernel/ti-linux-kernel.git
$ cd ti-linux-kernel

Get 4.4.y remote branch:

$ git checkout linux-4.4.y -b linux-4.4

Configure kernel

Make omap2plus default defconfig:

$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- omap2plus_defconfig

Make some modifications:

$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- omap2plus_defconfig

• Enable SPIDEV

Device Drivers  --->
   [*] SPI support  --->
       <M>   User mode SPI device driver support

• Enable DRM

Device Drivers  --->
   Graphics support  --->
       <M> Direct Rendering Manager (XFree86 4.1.0 and higher DRI support)  --->
       <M> DRM Support for TI LCDC Display Controller
           [*]   Support device tree blobs using TI LCDC Slave binding (NEW)

• Enable SHAM and AES

-*- Cryptographic API  --->
   [*]   Hardware crypto devices  --->
       <M>   Support for OMAP MD5/SHA1/SHA2 hw accelerator
       <M>   Support for OMAP AES hw engine

Kernel build

Build kernel and modules:

$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- zImage modules

Install modules to target directory:

$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- INSTALL_MOD_PATH=output modules_install

Patch kernel tree to get our device-tree blobs:

$ git apply 0001-Add-support-for-OLIMEX-dtbs.patch

If patch fail, you can reset the tree:

$ git reset --hard 65fd19fc2bac06ae7e66cc3d6450c9d6dd034311

Build dtbs:

$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- dtbs

This will produce lot of .dtb files. The interesting ones are:

• am335x-olimex-som.dtb - The minimum configuration for AM335x-SOM to run.
• am335x-olimex-som-nand.dtb - Same as above, but with enabled nand.
• am335x-olimex-som-evb.dtb - Support for AM335x-SOM-EVB. Use this one, if there isn't intalled nand on AM335x-SOM
• am335x-olimex-som-evb-nand.dtb - Save above, without dual ethernet and enabled nand.

File system

Debian 8

Install required tools:

$ sudo apt-get install qemu-user-static debootstrap binfmt-support 

Make target directory:

$ mkdir rootfs
$ sudo debootstrap --arch=armhf --foreign jessie rootfs 

Copy qemu and resolvonf:

$ sudo cp /usr/bin/qemu-arm-static rootfs/usr/bin/
$ sudo cp /etc/resolv.conf rootfs/etc 

Go into the new file system:

$ sudo chroot rootfs 

Inside the new file system do:

# export LANG=C
# /debootstrap/debootstrap --second-stage

Set apt sources.list:

# cat << __EOF__ > /etc/apt/sources.list
#------------------------------------------------------------------------------#
#                   OFFICIAL DEBIAN REPOS                    
#------------------------------------------------------------------------------#

###### Debian Main Repos
deb http://ftp.bg.debian.org/debian/ jessie main contrib non-free 
deb-src http://ftp.bg.debian.org/debian/ jessie main contrib non-free 

###### Debian Update Repos
deb http://security.debian.org/ jessie/updates main contrib non-free 
deb http://ftp.bg.debian.org/debian/ jessie-proposed-updates main contrib non-free 
deb-src http://security.debian.org/ jessie/updates main contrib non-free 
deb-src http://ftp.bg.debian.org/debian/ jessie-proposed-updates main contrib non-free 
__EOF__

Note: The list is generated using this tool, so feel free modify it.

Set hostname:

# echo "AM335x" > /etc/hostname

Install some packages:

# apt-get install locales dialog sudo openssh

Set locales:

# dpkg-reconfigure locales

Set root password:

# passwd

Add olimex user:

# adduser olimex

Enable serial port on USB-OTG

Make script that initialize serial gadget:

# cat << __EOF__ > /usb/bin/usb_serial.sh
#/bin/sh

# variables and strings
CONFIGS_DIR="/configs"
MANUFACTURER="Olimex Ltd."          #  manufacturer attribute
SERIAL=$(ifconfig eth0 | head -n1 | awk -F" " '{print $5}' | sed 's/://g')
IDPRODUCT="0x003e"                  #  hex product ID, issued by USB Group
IDVENDOR="0x15ba"                   #  hex vendor ID, assigned by USB Group
PRODUCT="AM335x Serial Gadget"      #  cleartext product description
CONFIG_NAME="Configuration 1"       #  name of this configuration
UDC=musb-hdrc.0.auto                #  name of the UDC driver to use (found in /sys/class/udc/)

# Load modules
! lsmod | grep "libcomposite" > /dev/null 2>&1 && modprobe libcomposite
! lsmod | grep "usb_f_acm" > /dev/null 2>&1 && modprobe usb_f_acm

# Mount confgsfs
[ ! -d $CONFIGS_DIR ] && mkdir $CONFIGS_DIR
mount none $CONFIGS_DIR -t configfs

# Create gadget
mkdir -p $CONFIGS_DIR/usb_gadget/serial
cd $CONFIGS_DIR/usb_gadget/serial

# Set VID and PID
echo $IDVENDOR > idVendor
echo $IDPRODUCT > idProduct

# Set strings
mkdir strings/0x409
echo $SERIAL > strings/0x409/serialnumber
echo $MANUFACTURER > strings/0x409/manufacturer
echo $PRODUCT > strings/0x409/product

# Create configuration
mkdir configs/c.1
mkdir configs/c.1/strings/0x409
echo "120" > configs/c.1/MaxPower
echo $CONFIG_NAME > configs/c.1/strings/0x409/configuration

# Creating functions
mkdir functions/acm.usb0

# Associate function with comfiguration
ln -s functions/acm.usb0 configs/c.1

# Enable UDC
echo $UDC > UDC
__EOF__
# chmod +x /usb/bin/usb_serial.sh

Add startup service:

# cat << _EOF__ > /lib/systemd/system/usb-serial.service
[Unit]
Description=Serial console on USB-OTG
ConditionPathExists=/sys/devices/platform/ocp/47400000.usb/47401300.usb-phy/
Before=serial-getty@ttyGS0.service

[Service]
Type=oneshot
ExecStart=/bin/bash -c "/usr/bin/usb_serial.sh"
RemainAfterExit=yes

[Install]
WantedBy=getty.target
__EOF__

Enable login on ttyGS0:

# cp -v /lib/systemd/system/serial-getty\@.service 
# nano /lib/systemd/system/serial-getty\@ttyGS0.service

Add following in [Unit] section:

Requires=usb-serial.service
# systemctl enable serial-getty\@ttyGS0.service