TS-4100 U-boot Sections

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
MMC:   FSL_SDHC: 0, FSL_SDHC: 1
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.

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.

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.

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

U-Boot Commands

# The most important command is 
help
# 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
bbdetect
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.
bootm
# 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
bootz
# 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
dhcp
# 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
fuse

# 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.
mtest

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

# The NFS command is like 'load', but used over the network
dhcp
env set serverip 192.168.0.11
nfs ${loadaddr} 192.168.0.11:/path/to/somefile

# Test ICMP
dhcp
ping 192.168.0.11

# Reboot
reset

# 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
else
	echo Could not find kernel
fi

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

# Print U-Boot version/build information
version