U-boot USB boot

Our U-Boot by default will attempt to read a U-Boot script named /tsinit.ub from a USB drive on bootup. If present on the USB drive, U-Boot will automatically load this script in to memory and execute it. For our bootable USB disk images, no further action is needed.

To make a bootable drive from scratch, create a single ext3 partition on a USB drive and copy over your preferred rootfs just like you would with an SD card. This is described in the Debian and Yocto sections.

The one addition is to create the /tsinit.ub file in the root of the USB drive in order to allow U-Boot to boot from the drive's contents.

Create the file /tsinit.scr in the root of the USB drive with the Linux filesystem:

# Prepare with:
# mkimage -A arm -T script -C none -n 'mx6 usb' -d tsinit.scr tsinit.ub

# DO NOT MANUALLY EDIT THE .UB FILE

# If loading files from a partition other than the first partition on disk, change
# the second number to the partition number
env set bootpart 0:1

if test ${model} = '4900';
	then load usb 0:1 ${loadaddr} /boot/ts4900-fpga.bin;
	ice40 ${loadaddr} ${filesize};

	bbdetect;

	# Check rev, attempt to load the best dtb file for compatibility. If Rev E files
	# are not found, attempt to boot prior dtb. If not Rev E, just boot prior dtb.
	if test ${rev} > 'D'; then
		if load usb ${bootpart} ${fdtaddr} /boot/imx6${cpu}-ts4900-reve-${baseboardid}.dtb
			then echo Baseboard $baseboardid detected;
		elif load usb ${bootpart} ${fdtaddr} /boot/imx6${cpu}-ts4900-reve.dtb
			then echo Booting default Rev E device tree;
		elif load usb ${bootpart} ${fdtaddr} /boot/imx6${cpu}-ts4900-${baseboardid}.dtb
			then echo Baseboard $baseboardid detected;
		elif load usb ${bootpart} ${fdtaddr} /boot/imx6${cpu}-ts4900.dtb
			then echo Booting default device tree;
		fi
	else
		if load usb ${bootpart} ${fdtaddr} /boot/imx6${cpu}-ts4900-${baseboardid}.dtb
			then echo Baseboard $baseboardid detected;
		elif load usb ${bootpart} ${fdtaddr} /boot/imx6${cpu}-ts4900.dtb
			then echo Booting default device tree;
		fi
	fi

	load usb ${bootpart} ${loadaddr} ${uimage};
	setenv bootargs root=/dev/sda1 rootwait rw ${cmdline_append};
	bootm ${loadaddr} - ${fdtaddr};

elif test ${model} = '7970'; then
	# Check for Rev F or newer. If so, load that dtb. If Rev F dtb does not exist
	# fall back to a prior dtb. If earlier Rev PCB, use prior dtb.
	if test ${rev} > 'E'; then
		if load usb ${bootpart} ${fdtaddr} /boot/imx6${cpu}-ts7970-revf.dtb; then
			echo Loaded TS-7970 Rev F device tree;
		elif load usb ${bootdev} ${bootpart} ${fdtaddr} /boot/imx6${cpu}-ts7970.dtb; then
			echo Loaded TS-7970 device tree;
		fi
	else
		if load usb ${bootdev} ${bootpart} ${fdtaddr} /boot/imx6${cpu}-ts7970.dtb; then
			echo Loaded TS-7970 device tree;
		fi
	fi

	load usb 0:1 ${loadaddr} ${uimage};
	setenv bootargs root=/dev/sda1 rootwait rw ${cmdline_append};
	bootm ${loadaddr} - ${fdtaddr};
fi

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

mkimage -A arm -T script -C none -n 'mx6 usb' -d tsinit.scr tsinit.ub

You may need to install u-boot-tools or the equivalent package for your distribution.