Embedded Linux Development on C.H.I.P¶

The intention with this guide is to give a brief introduction to compiling your sources. It is by no means complete. The guide aims to be as generic as possible. So no editor/ide specific details will be added (hopefully).

General Hardware Information¶

ARM CortexTM-A8 Core
ARMv7 Instruction set plus Thumb-2 Instruction Set
32KB Instruction Cache and 32KB Data Cache
256KB L2 Cache
3D Graphic Engine
Support Open GL ES 1.1/2.0 and open VG 1.1
Support multi-format video decoding, including VP6/8, AVS, H.264, H.263 , MPEG-1/2/4, etc
Up to 1080p@30fps resolution in all formats

You can find the datasheet in the git repo CHIP-Hardware.

Toolchain¶

In this section a list of many available toolchains will be added over time.

Buildroot¶

Essentially ::: $ git clone –branch chip/stable https://github.com/NextThingCo/CHIP-buildroot.git ~/chip-buildroot $ cd chip-buildroot $ make chip_defconfig $ make menuconfig Add/remove packages $ make linux-menuconfig Add/remove kernel features/drivers $ make

The resulting images will be found under output/images

Yocto¶

There are nightly toolchain installer builds available from autobuilder.yoctoproject.org. So you could simply download the arm toolchain from there. You can download the latest build from [here].

In order to build the default configuration make sure you have the following packages installed: git, diffstat, unzip, texinfo, python2, chrpath, wget, xterm, sdl, socat, cpio and lzop

Compile your own toolchain¶

In order to compile it yourself, we need to do a little more. To compile a toolchain using yocto, we need first to download the sources and setup the build environment.

::: $ git clone –branch fido git://git.yoctoproject.org/poky.git ~/poky $ cd poky && source oe-init-build-env build-chip-toolchain

Any armv7 toolchain should suffice. As basis for the toolchain we are going to use a MACHINE with the same instruction set (armv7). As an example, the olinuxino-a13 machine from meta-sunxi bitbake layer have the armv7 instruction set.

::: $ git clone https://github.com/linux-sunxi/meta-sunxi

Add the path to the layer in BBLAYERS variable by editing ~/poky/build-chip-toolchain/conf/bblayers.conf

::

BBLAYERS ?= “: /home/user/poky/meta /home/user/poky/meta-yocto /home/user/poky/meta-yocto-bsp /home/user/meta-sunxi “

Now edit the ~/poky/build-chip-toolchain/conf/local.conf and change the machine to an Allwinner A13 machine.

::: MACHINE ?= olinuxino-a13

Time to build the toolchain, simply type

::: $ bitbake -k meta-toolchain

You can now find the toolchain installer under ~/poky/build-chip-toolchain/tmp/deploy/sdk

Install the toolchain¶

The install script have a few options you may or may not wish to tweak. ::

Usage: poky-glibc-x86_64-meta-toolchain-armv7a-vfp-neon-toolchain-1.8.sh [-y] [-d <dir>]”

-y: Automatic yes to all prompts”
-d <dir>: Install the SDK to <dir>”

======== Advanced DEBUGGING ONLY OPTIONS ========”

-S: Save relocation scripts”
-R: Do not relocate executables”
-D: use set -x to see what is going on”

To install the toolchain simply run the following as superuser (sudo, su etc), it requires superuser because default installation dir is /opt. ::

# cd /home/user/poky/build-chip-toolchain/tmp/deploy/sdk # ./poky-glibc-x86_64-meta-toolchain-armv7a-vfp-neon-toolchain-1.8.sh -y

If you downloaded the pre-built toolchain then it would have been named poky-glibc-x86_64-core-image-sato-armv7a-vfp-neon-toolchain-1.8+snapshot.sh.

U-boot¶

The universal bootloader.

Compile U-boot¶

In order to build the bootloader, first make sure your toolchain is ready to use. ::: $ source /opt/poky/1.8/environment-setup-armv7a-vfp-neon-poky-linux-gnueabi $ echo “[$ARCH]$CROSS_COMPILE” [arm]arm-poky-linux-gnueabi-
When the toolchain is ready to use, get the u-boot sources and compile them. ::: $ git clone –branch nextthing/CHIP https://github.com/NextThingCo/CHIP-u-boot.git chip-u-boot $ cd chip-u-boot $ make CHIP_defconfig $ make

U-boot Commands¶

The following section describes the most important commands available in U-Boot. Please note that U-Boot is highly configurable, so not all of these commands may be available in the configuration of U-Boot installed on your hardware, or additional commands may exist. You can use the help command to print a list of all available commands for your configuration.

Here is a list of some common commands that may exist in your u-boot configuration::

Information Commands bdinfo - Print Board Info structure coninfo - Print console devices and informations flinfo - Print FLASH memory information iminfo - Print header information for application image help - Print online help

Memory Commands base - Print or set address offset crc32 - Checksum calculation cmp - Memory compare cp - Memory copy md - Memory display mm - Memory modify (auto-incrementing) mtest - Simple RAM test mw - Memory write (fill) nm - Memory modify (constant address) loop - Infinite loop on address range

Flash Memory Commands cp - Memory copy flinfo - Print FLASH memory information erase - Erase FLASH memory protect - Enable or disable FLASH write protection mtdparts - Define a Linux compatible MTD partition scheme

Execution Control Commands source - Run script from memory bootm - Boot application image from memory go - Start application at address ‘addr’

Download Commands bootp - Boot image via network using BOOTP/TFTP protocol dhcp - Invoke DHCP client to obtain IP/boot params loadb - Load binary file over serial line (kermit mode) loads - Load S-Record file over serial line rarpboot - Boot image via network using RARP/TFTP protocol tftpboot - Boot image via network using TFTP protocol

Environment Variables Commands printenv - Print environment variables saveenv - Save environment variables to persistent storage setenv - Set environment variables run - Run commands in an environment variable bootd - Boot default, i.e., run ‘bootcmd’

Flattened Device Tree support fdt addr - Select FDT to work on fdt list - Print one level fdt print - Recursive print fdt mknode - Create new nodes fdt set - Set node properties fdt rm - Remove nodes or properties fdt move - Move FDT blob to new address fdt chosen - Fixup dynamic info

Special Commands i2c - I2C sub-system

Miscellaneous Commands echo - Echo args to console reset - Perform RESET of the CPU sleep - Delay execution for some time version - Print monitor version ? - Alias for ‘help’

You can find details about the commands from www.denx.de

Linux Kernel¶

Install build dependencies¶

gcc, etc..

Compile Linux Kernel¶

In order to build the kernel, first make sure your toolchain is ready to use. ::: $ source /opt/poky/1.8/environment-setup-armv7a-vfp-neon-poky-linux-gnueabi $ echo “[$ARCH]$CROSS_COMPILE” [arm]arm-poky-linux-gnueabi-
When the toolchain is ready to use, get the linux sources for C.H.I.P and compile them. ::: $ git clone https://github.com/NextThingCo/CHIP-linux.git chip-linux $ cd chip-linux $ make sunxi_defconfig $ make

Device Tree Compilation¶

The DTS file needs to be compiled into a DTB file that the kernel can understand. The device tree compiler (DTC), located under scripts/dtc in the linux kernel source, will compile the DTS file into a DTB file with the command::: $ ./scripts/dtc/dtc -I dts -O dtb -o devicetree.dtb CHIP.dts
The DTC compiler can also de-compile a DTB file back to the DTS file with the command::: $ ./scripts/dtc/dtc -I dtb -O dts -o CHIP.dts devicetree.dtb
You can view other options for the DTC compiler with the -h option::: $ ./scripts/dtc/dtc -h