TS-4100 U-boot Sections

From Technologic Systems Manuals

This platform includes U-Boot as the bootloader to load and boot the full operating system. The i.MX6UL processor loads U-Boot from the eMMC flash at power-on. U-Boot allows booting images from the microSD, eMMC, NFS, or USB. U-Boot is a general purpose bootloader that is capable of booting into common Linux distributions, Android, QNX, or others.

On a normal boot, output from U-Boot will be similar to the following:

U-Boot 2016.03-00367-gb3ce405827 (Jul 02 2019 - 16:40:10 -0700)

CPU:   Freescale i.MX6UL rev1.1 at 396 MHz
Reset cause: POR
Board: Technologic Systems TS-4100
FPGA:  Rev 11
Silab: Rev 2
I2C:   ready
DRAM:  1 GiB
Baseboard ID: 0x8
Baseboard Rev: 0
Net:   FEC0 [PRIME]
Press Ctrl+C to abort autoboot in 1 second(s)
starting USB...
USB0:   USB EHCI 1.00
scanning bus 0 for devices... 1 USB Device(s) found
USB1:   USB EHCI 1.00
scanning bus 1 for devices... 1 USB Device(s) found
       scanning usb for storage devices... 0 Storage Device(s) found
No storage devices, perhaps not 'usb start'ed..?
Booting from the SD card ...
** File not found /boot/boot.scr **
** File not found /boot/ts4100-fpga.vme **
29205 bytes read in 146 ms (195.3 KiB/s)
8 detected
5244088 bytes read in 390 ms (12.8 MiB/s)
Kernel image @ 0x80800000 [ 0x000000 - 0x5004b8 ]
## Flattened Device Tree blob at 83000000
   Booting using the fdt blob at 0x83000000
   Using Device Tree in place at 83000000, end 8300a214

Starting kernel ...

When running standalone, the TS-4100 will default to booting from eMMC. This behavior can be changed by modifying the U-Boot environment variable "force_jpsdboot". Normally this variable does not exist in the U-Boot environment, if it does exist, setting it to a value of 1 will force U-Boot to attempt to boot from microSD. If it is set to a value of 0, then U-Boot will attempt to boot from eMMC. Additionally, running U-Boot commands are used direct booting to another source such as NFS, USB, or microSD.

Many of our compatible baseboards offer an "SD Boot" jumper to control the behavior between SD and eMMC. See the specific baseboard manual for the combination being used for more detailed information. If designing a custom baseboard, we recommend reviewing our custom baseboard design recommendations for better controlling boot flow with U-Boot.

1 Entering U-Boot Shell

The U-Boot shell is a powerful tool. It allows modification of the environment, as well as the ability to run commands directly.

Under most circumstances the U-Boot environment is set up to handle most boot situations, however it may be necessary to modify the environment. When using any of the following methods to enter the U-Boot shell, this will cause U-Boot to read a script file from an attached USB mass storage device before dropping to the U-Boot shell. This will happen regardless even if USB boot is disabled for normal boot.

When the TS-4100 is booted standalone, a prompt is provided by U-Boot to press ctrl+c followed by a 1 second window. If ctrl+c is found incoming on the serial terminal within this time window then U-Boot will drop to its shell. This behavior can be modified by setting the U-Boot environment variable force_bootdelay. Normally this variable does not exist in U-Boot environment, if it does, it will force the timeout for pressing ctrl+c to be however many seconds the variable is set to. If it is set to 0, then the ctrl+c prompt is skipped.

Note: Use caution when setting "force_bootdelay", a value of 0 means it is no longer possible to enter the U-Boot shell without booting the device on a compatible baseboard that has a "U-Boot" jumper!

On our compatible baseboards or custom designed baseboards there are two ways to break in to the U-Boot shell. Note that some compatible baseboards may still offer a prompt as outlined above. See the specific baseboard manual for the combination being used for more detailed information.

The baseboard has a "U-Boot" jumper. When set, this will cause U-Boot to read a script file from an attached USB mass storage device before dropping to the U-Boot shell. When the jumper is not set, the unit will boot as normal. See our custom baseboard design recommendations for information on how the U-Boot jumper should be set up in order to be supported by our default U-Boot configuration.

The baseboard offers a push switch which is broken out from pin 9 on CN1 of the TS-4100. This button can be held down before applying power, and at least 5 seconds after power is applied.

This allows for out of the box functionality and customized production via a USB drive. In order to provide increased security, the push switch entry to U-Boot can be disabled via the U-Boot environment variable rstuboot. The following U-Boot commands can be used to disable the push switch check, thereby preventing it from being able to enter the U-Boot shell.

env set rstuboot 0
env save

Removing the rstuboot environment variable, or setting it to a 1, will re-enable the ability for the push switch to interrupt U-Boot and drop to its shell. See our custom baseboard design recommendations for information on how the push switch should be set up in order to be supported by our default U-Boot configuration.

On baseboards that support both a jumper and the push switch, disabling the push switch will still allow the jumper method of entering the U-Boot shell.

2 U-Boot Environment

The eMMC flash contains both the U-Boot executable binary and U-Boot environment. Our default build has 2 MiB of environment space which can be used for variables and boot scripts. The following commands are examples of how to manipulate the U-Boot environment:

# Print all environment variables
env print -a

# Sets the variable bootdelay to 5 seconds
env set bootdelay 5;

# Variables can also contain commands
env set hellocmd 'led red on; echo Hello world; led green on;'

# Execute commands saved in a variable
env run hellocmd;

# Commit environment changes to the SPI flash
# Otherwise changes are lost
env save

# Restore environment to default
env default -a

# Remove a variable
env delete emmcboot

3 U-Boot Commands

# The most important command is 
# This can also be used to see more information on a specific command
help i2c

# This is a command added to U-Boot by TS to read the baseboard ID on our 
# System on Module devices
echo ${baseboard} ${baseboardid} 
# The echo will return something similar to:
# TS-8390 2

# Boots into the binary at $loadaddr.  The loaded file needs to have
# the U-Boot header from mkimage.  A uImage already contains this.
# Boots into the binary at $loadaddr, skips the initrd, specifies
# the FDT addrress so Linux knows where to find the device tree
bootm ${loadaddr} - ${fdtaddr}

# Boot a Linux zImage loaded at $loadaddr
# Boot in to a Linux zImage at $loadaddr, skip initrd, specifies
# the FDT address to Linux knows where to find the device tree
bootz ${loadaddr} - ${fdtaddr}

# Get a DHCP address
# This sets ${ipaddr}, ${dnsip}, ${gatewayip}, ${netmask}
# and ${ip_dyn} which can be used to check if the dhcp was successful

# These commands are used for scripting:
false # do nothing, unsuccessfully
true # do nothing, successfully

# This command can set fuses in the processor
# Setting fuses can brick the unit, will void the warranty,
# and should not be done in most cases

# GPIO can be manipulated from U-Boot.  Keep in mind that the IOMUX 
# in U-Boot is only setup enough to boot the device, so not all pins will
# be set to GPIO mode out of the box.  Boot to the full operating system
# for more GPIO support.
# GPIO are specified in bank and IO in this manual.  U-Boot uses a flat numberspace,
# so for bank 2 DIO 25, this would be number (32*1)+25=89
# The formula thus being (32*(bank-1)+dio)=flattened_dio
# Note that on some products, bank 1 is the first bank
# Set 2_25 low
gpio clear 83
# Set 2_25 high
gpio set 83
# Read 2_25
gpio input 83

# Control LEDs
led red on
led green on
led all off
led red toggle

# This command is used to copy a file from most devices
# Load kernel from SD
load mmc 0:1 ${loadaddr} /boot/uImage
# Load Kernel from eMMC
load mmc 1:1 ${loadaddr} /boot/uImage
# Load kernel from USB
usb start
load usb 0:1 ${loadaddr} /boot/uImage
# Load kernel from SATA
sata init
load sata 0:1 ${loadaddr} /boot/uImage

# View the FDT from U-Boot
load mmc 0:1 ${fdtaddr} /boot/imx6q-ts4900.dtb
fdt addr ${fdtaddr}
fdt print

# It is possible to blindly jump to any memory location
# This is similar to bootm, but it does not require
# the use of the U-Boot header
load mmc 0:1 ${loadaddr} /boot/custombinary
go ${loadaddr}

# Browse fat, ext2, ext3, or ext4 filesystems:
ls mmc 0:1 /

# Access memory like devmem in Linux, read/write arbitrary memory
# using mw and md
# write
mw 0x10000000 0xc0ffee00 1
# read
md 0x10000000 1

# Test memory.

# Check for new SD card
mmc rescan
# Read SD card size
mmc dev 0
# Read eMMC Size
mmc dev 1

# The NFS command is like 'load', but used over the network
env set serverip
nfs ${loadaddr}

# Test ICMP

# Reboot

# SPI access is through the SF command
# Be careful with sf commands since
# this is where U-Boot and the FPGA bitstream exist
# Improper use can render the board unbootable
sf probe

# Delay in seconds
sleep 10

# Load HUSH scripts that have been created with mkimage
load mmc 0:1 ${loadaddr} /boot/ubootscript
source ${loadaddr}

# Most commands have return values that can be used to test
# success, and HUSH scripting supports comparisons like
# test in Bash, but much more minimal
if load mmc 1:1 ${fdtaddr} /boot/uImage;
	then echo Loaded Kernel
	echo Could not find kernel

# Commands can be timed with "time"
time sf probe

# Print U-Boot version/build information

4 Modify Linux Kernel cmdline

The Linux kernel cmdline can be customized by modifying the cmdline_append variable. If new arguments are added, the existing value should also be included with the new arguments.

env set cmdline_append rw rootwait console=ttymxc0,115200 quiet
env save

The kernel command line can also be modified from from within Linux by creating a U-Boot script. From the Linux shell prompt run the following commands to install the necessary tools and create the script:

apt-get update && apt-get install u-boot-tools -y
echo "env set cmdline_append rw rootwait console=ttymxc0,115200 quiet" > /boot/boot.source
mkimage -A arm -T script -C none -n 'tsimx6ul boot script' -d /boot/boot.source /boot/boot.scr

The boot.source includes the plain text commands to be run in U-Boot on startup. The mkimage tool adds a checksum and header to the output file which then can be loaded by U-Boot. The .scr file should not be edited directly.

By default, every boot to SD, eMMC, and NFS will look for the file "/boot/boot.scr" and attempt to load and run it if it exists. This allows for modification of the boot process dynamically every boot without having to enter the U-Boot shell and modify it.

5 Linux NFS Boot

U-Boot's NFS support can be used to load a kernel, device tree binary, and root filesystem. The default scripts include an example NFS boot script. Because of the way U-Boot tries to infer server data, the script we use will bypass this, making it more straightforward to use an NFS root that will not be heavily dependent on a particular network configuration.

# Set this to your NFS server IP
env set nfsip
# Set this to your NFS root path
env set nfsroot /path/to/nfs/rootfs/
env save

To boot to NFS root once the server details are set:

# Boot to NFS once
run nfsboot;

# To make the NFS boot the persistent default
env set bootcmd run nfsboot;
env save
Note: 'bootcmd' is used to test for whether the system should stop at the U-Boot shell or continue, the above will make it difficult to get back to the U-Boot shell as it will always attempt to boot regardless of jumper status.

On the TS-4100, U-Boot will only boot to the network from the first physical port. The port that Linux considers to be "eth1".

6 Linux USB Boot

By default, U-Boot will attempt to read a U-Boot script from a USB drive on every bootup. This process copies /tsinit.scr from the first partition of the USB drive into memory and jumps in to the script. If the drive or script do not exist, then this process is bypassed and U-Boot will continue its boot flow.

This process is attempted on every boot unless it is disabled. It can be disabled by modifying the U-Boot environment variable usbboot. If usbboot is set to 0 then this step will be bypassed on normal boot cycles. It is enabled by default to allow for a custom production process to be used.

If the U-Boot shell is entered by holding the push switch or using the U-Boot jumper (on baseboards with either a push switch or U-Boot jumper), this process will always run before dropping to the U-Boot shell regardless of the state of the usbboot variable. If the U-Boot shell is entered by pressing ctrl+c (on boaseboards without a U-Boot jumper or TS-4100 standalone), then this process is never run since autoboot is aborted and the shell is immediately entered. In this state, the USB boot process can always be manually started with the command run usbprod.

For information on creating a USB drive to write existing images to either SD and/or eMMC, see the section on our custom production process for more details on the process.

To make a bootable USB drive that boots in to the same environment as SD or eMMC, create a single ext3 partition on a USB drive and unpack the rootfs tarball located here.

Additionally, a U-Boot script file, /tsinit.scr, must be created and placed in the root folder of this partition. In order to do this, a script must be created and converted to the U-Boot .scr format. This process requires a set of U-Boot specific tools. These tools are available on most every Linux distribution, the instructions below are for Debian, either on a host PC or on the device itself. See the package installation documentation for other respective distributions.

Install U-Boot tools in Debian

apt-get update && apt-get install u-boot-tools -y

Create the file "tsinit.source" in the root of the USB drive with the Linux filesystem:

# Prepare with:
# mkimage -A arm -T script -C none -n 'imx6ul usb' -d tsinit.source tsinit.scr


if load usb 0:1 ${loadaddr} /boot/ts${model}-fpga.vme;
        then fpga load 0 ${loadaddr} ${filesize};

if load usb 0:1 ${fdtaddr} /boot/imx6ul-ts${model}-${baseboardid}.dtb;
        then echo "${baseboardid} detected;"
else echo "Booting default device tree";
        load usb 0:1 ${fdtaddr} /boot/imx6ul-ts${model}.dtb;

load usb 0:1 ${loadaddr} /boot/zImage;
setenv bootargs root=/dev/sda1 rootwait rw ${cmdline_append} bbid=0x${baseboardid} bbrev=0x${baseboardrev};
run silowaitcharge;
bootz ${loadaddr} - ${fdtaddr};

Then in the same directory generate the tsinit.scr file:

mkimage -A arm -T script -C none -n 'imx6ul usb' -d tsinit.source tsinit.scr

7 Update U-Boot

WARNING: Installing a custom U-Boot is not recommended and may cause the device to fail to boot.

The TS-4100 uses slightly different U-Boot binaries for the 512 MB and 1 GB RAM variants. This is due to different DDR timing that needs to be set up at the start of U-Boot. When updating U-Boot, be sure to use the script that exists in U-Boot discussed below as it will use the correct file name and will reduce any potential issues

The latest U-Boot binary can be downloaded from the TS-4100 FTP site. Copy these files to /boot/ on the 1st partition of the SD card (or eMMC). The U-Boot binary can be updated by inserting that SD card in to the TS-4100, setting the jumpers to boot from SD, power up the unit, and enter the U-Boot shell. At the U-Boot prompt, the following command can be used:

run update-uboot

The above script will use the /boot/u-boot-${imx_type}.imx file from the SD card or eMMC, depending on the state of the SD Boot jumper.

Note that when running the TS-4100 standalone, the "update-uboot" command will default to searching the eMMC. Setting the environment variable "jpsdboot" to "on" (do not save the environment to disk otherwise it may cause booting issues later!), and then running the 'run update-uboot' command will cause U-Boot to look in "/boot" on the first SD card partition for the update files necessary.

8 U-Boot Development

We do provide our U-Boot sources, but we do not recommend rebuilding a custom U-Boot binary as it can leave the system in an unbootable state.

If proceeding with building a custom U-Boot, use the "tsimx_v2016.03_4.1.15_2.0.0_ga" branch from our github repo: https://github.com/embeddedarm/u-boot-imx this can be executed with the following command:

git clone https://github.com/embeddedarm/u-boot-imx.git -b tsimx_v2016.03_4.1.15_2.0.0_ga u-boot-ts4100

When compiling, we recommend using ONLY this cross-compiler, the use of any other compiler may cause issues or may leave the system in an unbootable state! Specifically, we have experienced RAM problems when using a more recent cross compiler to build this version of U-Boot. The tarball can be extracted with the following:

mkdir /opt/toolchains/ts4100/
tar -xf tsimx6ul-glibc-gnueabihf-4.9.4.tar.xz -C /opt/toolchains/ts4100/

Once the tarball has been properly extracted set up the following variables and run the build script:

export ARCH=arm
export CROSS_COMPILE=/path/to/folder/bin/arm-tsimx6ul-linux-gnueabihf-

After the environment variables have been set up as shown above the build is now ready to be executed:

cd /path/to/u-boot-imx
./build-imx6ul.sh ts4100

This will output binaries for 1 GB and 512 MB RAM variants in "/u-boot-imx/out/" that can be written to the device using the steps in Update U-Boot.

Note: If the following error message is received: "error while loading shared libraries: libmpfr.so.4: cannot open shared object file:" create the following symbolic link in Debian:
sudo ln -s /usr/lib/x86_64-linux-gnu/libmpfr.so.6 /usr/lib/x86_64-linux-gnu/libmpfr.so.4


The TS-4100 U-Boot includes a simple POST test. This is normally used in production to verify basic functionality rapidly before continuing to more thorough testing. By default, this is not enabled on every boot, but it can be added via U-Boot scripting if there is a need for additional confidence in the application. The POST test quickly verifies basic functionality of: USB, RTC (if present), Ethernet PHY, WiFi/BT module (if present), eMMC (see warning below), RAM, and the supervisory microcontroller.

The post test can be run with the following command in U-Boot:

WARNING: The 'post' command has an optional "-d" argument; when this argument is passed it does a write and readback test of the eMMC and any other soldered down flash media on the TS-4100 or baseboards which is DESTRUCTIVE to the data on the disk! Note that it will not modify the boot sector contents of the eMMC which is needed by U-Boot. The eMMC chip is still tested for basic functionality without the argument passed, but no data is read or written from the disk itself.