BSP Documentation 5.4

Yocto Build Guide 5.4

Development Machine Requirements

• 8GB of memory minimum

• 300GB of Disk Space available

• Ubuntu 20.04

Steps to build

1. Pull in packages needed for the build.
   sudo apt install gawk wget git-core diffstat unzip texinfo gcc-multilib \
build-essential chrpath socat libsdl1.2-dev

   sudo apt install libsdl1.2-dev xterm sed cvs subversion coreutils texi2html \
docbook-utils python-pysqlite2 help2man make gcc g++ desktop-file-utils \
libgl1-mesa-dev libglu1-mesa-dev mercurial autoconf automake groff zstd curl lzop asciidoc

   sudo apt install u-boot-tools

   sudo apt install python

2. Create a project directory. Doesn’t have to be ~/winYocto.
   mkdir ~/winYocto

3. Configure git.
   git config --global user.name "Your Name"
git config --global user.email "Your Email"
git config --list

4. Install repo tool
   mkdir ~/bin
curl https://storage.googleapis.com/git-repo-downloads/repo > ~/bin/repo
chmod a+x ~/bin/repo
export PATH=~/bin:$PATH

5. Download the Yocto Project layers for building the c444 image.
   cd ~/winYocto
repo init -u https://github.com/WinSystems/c444-manifest.git -b master -m itx-p-c444_5.4.24.xml
repo sync

6. Configure the build directory to target the c444.
   MACHINE=imx8mq-itx-p-c444 DISTRO=c444-xwayland source winsys-setup-release.sh -b build

7. Run the following to avoid Chromium build failures.
   ulimit -n 10000

8. Accept the EULA, and begin building the image. In this case the image will be the winsys-image-demo, but there are other target builds available.
   bitbake -k winsys-image-demo

   bitbake NOTES:
   a. The bitbake -k option allows bitbake to continue building as much as it can if there is an error.
   b. bitbake will need to be executed multiple times before successfully completing.
   c. If a package continues to fail bitbake, run the code below, then rerun the bitbake command from Step 8.
   bitbake -c cleanall <recipe-name>

9. Once the build has completed the image will be under tmp/deploy/images/imx8mq-itx-p-c444.

The files needed to flash a μSD are winsys-image-demo-imx8mq-itx-p-c444.wic.bz2 and winsys-image-demo-imx8mq-itx-p-c444.wic.bmap

The files needed to flash the eMMC using uuu are winsys-image-demo-imx8mq-itx-p-c444.rootfs.tar.bz2 and imx-boot-imx8mq-itx-p-c444-sd.bin-flash_evk

Steps to program the new BSP image

Updating the BSP on the eMMC

Updating the BSP on the μSD

Image Usage

Accessing U-Boot

The U-Boot console by default is piped out over UART1 at 115200 baud. Press any key during boot to stop it from running the default boot command. It has a three second delay by default before it runs the boot command.
Common u-boot commands:
?
Prints out help with all the commands it supports

printenv
Prints out a list of all the environment variables

setenv [variable to set] '[value to set it to]'
Sets the environment variable to desired value

saveenv
Preserves all of the current environment variables between resets.

env default -a
Sets all the environment variables back to defaults

Switching Device Trees

The image produced by the winsys-image-demo target provides two device trees. One supports HDMI and the other supports a 1024x768 LVDS panel. This is how to select the desired device tree from the u-boot prompt.
setenv fdtfile 'imx8mq-itx-p-c444-lvds-auo.dtb'
saveenv
The above switches to the panel device tree.
setenv fdtfile 'imx8mq-itx-p-c444.dtb'
saveenv
The above switches to the HDMI device tree

Switching Linux Boot Media

Linux can be booted from the eMMC or the μSD. Here are the u-boot commands for switching between the two boot media.
μSD boot:
setenv mmcroot '/dev/mmcblk0p2 rootwait rw'
setenv mmcdev 0
saveenv
boot
eMMC boot:
setenv mmcroot '/dev/mmcblk1p2 rootwait rw'
setenv mmcdev 1
saveenv
boot

Adjusting HDMI Resolution

HDMI supports the following resolutions: 640x480p60, 720x480p60, 1280x720p60, 1920x1080p60,3840x2160p60, 4096x2160p60, Here is how to change the resolution at the u-boot prompt.

1. setenv mmcargs 'setenv bootargs ${jh_clk} console=${console} root=${mmcroot} video=HDMI-A-1:[resolution goes here]@[refresh rate goes here]
2. saveenv
3. Boot Linux
4. Edit /etc/xdg/weston/weston.ini and make sure the following is present in the file:
   [output]
name=HDMI-A-1
mode=[resolution goes here]

Disabling Linux console

Doing the following will disable the console and make debug extremely difficult without reflashing the image. Proceed with caution.

1. Stop at uboot and type the following commands
   setenv console 'null'
setenv silent 1
saveenv
boot
2. Login to linux and run the following from the command line
   sudo systemctl disable serial-getty@ttymxc0.service
   The step above assumes the console was coming out over UART1

Adjusting U-Boot Delay

U-Boot inserts a time delay before running the boot command. The pause can be adjusted by changing the bootdelay environment variable. It will be difficult to break into u-boot if this variable is set too small.
setenv bootdelay [desired delay time in seconds]

Device Names in Linux

GPIO

GPIO # on Connector	GPIO # in Linux
1	0
2	1
3	3
4	5
5	6
6	7
Blue Status LED	84
Green User_LED	132

One way to configure and control the GPIO is via the sysfs interface. Here is how to export them so they can be accessed using that interface.
sudo sh -c 'echo [GPIO # in Linux] > /sys/class/gpio/export
From there a new folder at /sys/class/gpio/gpio[GPIO # in Linux] contains direction and value files. More information on the sysfs interface to GPIO can be found here.

UARTs

UART1 shows up as /dev/ttymxc0 and UART 2 shows up as /dev/ttymxc1