Table of Contents

Introduction

In the earlier post, we saw the boot process of Raspberry Pi 3 Model B and how to login to U-boot console. In this article we will see how to establish TFTP protocol communication between development system and RPI.

The development system acts like TFTP server and used to host the files which can be transferred to the RPI. After establishing TFTP communication, the U-boot will be able to download the files from TFTP server and load into the RAM. In the upcoming articles, we will be using this method to download Linux kernel and Device tree from the TFTP server to the Rapsberry Pi.

TFTP communication with Raspberry Pi 3 Model B
TFTP communication with Raspberry Pi 3 Model B

Setup the U-boot

Connect Rapberry PI to the Ubuntu system using Ethernet cable. Both Raspberry PI and the host system should belong to same network to be able to communicate.

Let’s setup some environment variables. Power up the Raspberry Pi, press Enter to login to U-boot console immediately after powerup. In the console, run the following commands.

setenv ipaddr 192.168.1.115
setenv serverip 192.168.1.15 # IP address of host system ethernet interface
saveenv

The environment variable ipaddr is the IP address of the Raspberry Pi. The serverip environment variable is system IP address in which TFTP server is running. I am using my development system as a TFTP server. This can be any system as long as it is in the same network as Raspberry Pi.

The environment variable saveenv saves the environment data to the SD card so that you don’t have to enter this data every time the board boots.

Set up the server

Please use this tutorial to install TFTP server in your development system (Ubuntu). Note down the tftp directory path. The default directory can be either /srv/tftp or /var/lib/tftpboot. This will be used to store the files which can be transferred to RPI.

Change the IP address of your Ubuntu system Ethernet interface IP address to the serverip address. In this case it is 192.168.1.15. The simple way to do this is using the following command.

nmcli con add type ethernet ifname <Ethernet_interface_name> ip4 192.168.1.15/24

Ex : nmcli con add type ethernet ifname enp3s0 ip4 192.168.1.15/24

You can find your Ethernet interface name from the command ifconfig -a.

Testing the connection

First change the ownership of the TFTP directory.

sudo chown -R USERNAME TFTP_DIRECTORY	# Replace USERNAME and TFTP_DIRECTORY with yours

Ex: sudo chown -R nayab /srv/tftp/

Let’s create a dummy file called testFile in the tftp directory of your host system.

echo "dummy data" > /srv/tftp/testFile

Use the following command in the Raspberry Pi U-boot console to download the file testFile from the TFTP server.

tftp 0x1000000 testFile

Make sure the file is transferred successfully. At the end of transmission, you should see the message similar to following.

Loading: ################################### 11 Bytes
         0 Bytes/s
done
Bytes transferred = 11 (b hex)
U-Boot>