Setting Up TFTP and NFS

The purpose of this document is to show how to set up a board to boot with TFTP and NFS. This is useful for developers so that they can rebuild and edit the kernel without having to unplug the SD card repeatedly.

Disclaimer: These instructions assume that the user is trying to build the ti-linux-6.6.y kernel and is using an SK-TDA4VM. The instructions should carry over to most (if not all) Jacinto devices however.

1. Requirements

2. Setting Up Hardware

2.1. Setting Up the Host

2.1.1. Installing Required Packages

sudo apt install network-manager

picocom is used to interface with the device over the serial port.

$ picocom -b 115200 /dev/ttyUSB2

2.1.2. Setting Up the Interface

Connect the board to the host machine. Note the interface that the board is associated with. The interface is likely to be enxxx. You can also check which interface appears with ifconfg when plugging in the cable.

# ethernet cable (and adapter) is unplugged
$ ifconfig
# note interfaces
# plug in cable
$ ifconfig
# note the new interface

You will then configure the interface's ip address.

$ nmcli con add type ethernet ifname <enxxx> ip4 192.168.1.1/24

2.2. Setting Up the Target

The target needs to have an SD card with a boot partition already set up. Primarily, the boot partition needs to contain the following files:

• tiboot3.bin
• tispl.bin
• u-boot.img
• uEnv.txt (not required)

This can be accomplished by flashing the SD card with a default wic image that corresponds with the board. There are other more involved ways to do it, but this is the easiest.

3. Building the Kernel

Hypothetically, you'll be rebuilding and reloading the kernel if you are developing with tftp and nfs. The following are steps to do that.

3.1. Downloading a Cross-compile Toolchain

$ wget https://developer.arm.com/-/media/Files/downloads/gnu/13.3.rel1/binrel/arm-gnu-toolchain-13.3.rel1-x86_64-aarch64-none-linux-gnu.tar.xz
$ tar -xf https://developer.arm.com/-/media/Files/downloads/gnu/13.3.rel1/binrel/arm-gnu-toolchain-13.3.rel1-x86_64-aarch64-none-linux-gnu.tar.xz
$ export PATH=$PATH:arm-gnu-toolchain-13.3.rel1-x86_64-aarch64-none-linux-gnu/bin
$ export ARCH=arm64
$ export CROSS_COMPILE=aarch64-none-linux-gnu-

3.2. Building the Kernel

$ git clone -b ti-linux-6.6.y https://git.ti.com/git/ti-linux-kernel/ti-linux-kernel.git 
$ cd ti-linux-kernel
$ make defconfig ti_arm64_prune.config
$ make -j`nproc` Image modules dtbs
$ cd ../

4. Setting Up TFTP

4.1. Installing Required Packages

$ sudo apt install tftpd-hpa

4.2. Exporting Files

Check which directory is being exported. The sed command sets TFTP_DIR to make copying future commands easier.

$ grep TFTP_DIRECTORY /etc/default/tftpd-hpa
$ export TFTP_DIR=`sed -n 's/TFTP_DIRECTORY="\(.*\)"/\1/p' /etc/default/tftpd-hpa`

Copy the kernel Image and device tree blob into the exported directory.

$ cp ti-linux-kernel/arch/arm64/boot/Image $TFTP_DIR/
$ cp ti-linux-kernel/arch/arm64/boot/dts/ti/k3-j721e-sk.dtb $TFTP_DIR/

If the tftp directory requires super user permissions to access, you can execute the following command to give your user read, write, and execution permissions:

$ sudo setfacl -m u:`whoami`:rwx $TFTP_DIR

4.3. Test TFTP

Reset your tftp server just to ensure there are no issues:

$ sudo /etc/init.d/tftpd-hpa restart

Boot the board and stop it at the u-boot prompt:

Hit any key to stop autoboot:  0
=>

Set environment variables:

=> setenv ipaddr 192.168.1.100
=> setenv serverip 192.168.1.1

Transfer the Image and device-tree blob:

=> tftp 0x80000000 Image
=> tftp 0x83000000 k3-j721e-sk.dtb

5. Setting Up NFS

5.1. Installing Required Packages

$ sudo apt install nfs-kernel-server

5.2. Setting Up the File System

Use a rootfs tarball for the relevant board. For example, you can use the tisdk-default-image-j721e-sk.rootfs.tar.xz. This can be built using Yocto.

$ mkdir nfsroot
$ tar -xf tisdk-default-image-j721e-sk.rootfs.tar.xz -C nfsroot
$ echo "$PWD/nfsroot 192.168.1.100(rw,no_root_squash,no_subtree_check)" >> /etc/exports
$ sudo exportfs -r

6. Boot the Board Using TFTP and NFS

Reset the board and stop at the u-boot prompt.

You'll need to replace the <nfsroot-directory> with the correct path.

=> setenv ipaddr 192.168.1.100
=> setenv serverip 192.168.1.1
=> setenv bootcmd 'tftp 0x80000000 Image; tftp 0x83000000 k3-j721e-sk.dtb; booti 0x80000000 - 0x83000000'
=> setenv bootargs root=/dev/nfs rw ip=192.168.1.100:::::eth0 console=ttyS2,115200n8 nfsroot=192.168.1.1:<nfsroot-directory>,nfsvers=3,tcp
=> boot

7. Additional Notes

• You should be able to set the environment variables within uEnv.txt if you want them to remain between resets.
• To apply a device-tree overlay, you can use the fdtoverlay application and then use newly generated device-tree blob to boot

$ fdtoverlay -i <base-dtb> -o <new-dtb> <overlay-dtbo>