Loading Linux Images via Ethernet and TFTP Print

This note explains how to load images to the target via Ethernet. With an Ethernet connection available, U-Boot can load images from a TFTP host quickly and easily. This is the development and software manufacturing option that is preferable with U-Boot and Linux.

The download procedure is based on the tftpboot command provided by the U-Boot command interface. tftboot implements a download capability over Ethernet using the TFTP protocol and has the following synopsis:

tftpboot <file> [<load_addr>]

If you do not specify a load address, then the value will be taken from the loadaddr environment variable. On the NXP i.MX RT1050 EVK board, loadaddr is set as follows, placing the download buffer into the on-module SDRAM:

=> print loadaddr

The MAC address of the Ethernet interface is defined by the ethaddr environment variable.The IP address of the board is defined by the ipaddr U-Boot environment variable. The TFTP server IP address is defined by the serverip U-Boot environment variable. Make sure you define these environment variables to values that make sense for your LAN and save them in the SD Card:

=> setenv ethaddr aa:bb:cc:dd:ee:d0
=> setenv ipaddr
=> setenv serverip
=> saveenv
Saving Environment to MMC... Writing to MMC(0)... OK

Once the transmission using tftpboot finishes, the file will be in memory at the specified load address. The loadaddr environment variable will automatically be set to the address the tftpboot command used. The filesize environment variable will automatically be set to the number of bytes transferred during the load operation.

Then you are free to do whatever you like with the loaded image. You can boot Linux from the image (assuming it is a Linux uImage file), display the memory, etc.

One typical command sequence involving tftpboot is defined in the netboot environment variable, which by default is set in U-Boot as follows:

=> print netboot
netboot=tftp ${tftpdir}${image} && run addip && bootm

What netboot does is load from tftpdir in a TFTP host a file defined by image (the tftp command), then add the TCP/IP related parameters to the kernel command string (addip), and finally boot Linux from the just loaded image (bootm).

Let's use netboot to boot Linux via TFTP from the sample Linux image (rootfs.uImage) included in the Emcraft software distribution. Copy rootfs.uImage to the appropriate (tftpdir) TFTP directory on the host and then from U-Boot on the target set the image environment variable to point to the image:

=> setenv image imxrt1050/rootfs.uImage => saveenv Saving Environment to MMC... Writing to MMC(0)... OK => run netboot Using ethernet@402D8000 device TFTP from server; our IP address is Filename 'imxrt1050/rootfs.uImage'. Load address: 0x80007fc0 ... ######################################################### 109.4 KiB/s done Bytes transferred = 8277462 (7e4dd6 hex) ## Booting kernel from Legacy Image at 80007fc0 ... Image Name: Linux-5.15.71 Image Type: ARM Linux Multi-File Image (uncompressed) Data Size: 8277398 Bytes = 7.9 MiB Load Address: 80008000 Entry Point: 80008001 Contents: Image 0: 8269856 Bytes = 7.9 MiB Image 1: 7530 Bytes = 7.4 KiB Verifying Checksum ... OK ## Flattened Device Tree from multi component Image at 80007FC0 Booting using the fdt at 0x807eb02c Loading Multi-File Image Loading Device Tree to 81e81000, end 81e85d69 ... OK Starting kernel ... Booting Linux on physical CPU 0x0 Linux version 5.15.71 (sasha@workbench.emcraft.com) (arm-none-eabi-gcc (GNU Arm Embedded Toolchain 10.3-2021.10) 10.3.1 20210824 (release), GNU ld (GNU Arm Embedded Toolchain 10.3-2021.10) #2 Mon Sep 25 08:03:11 UTC 2023 CPU: ARMv7-M [411fc271] revision 1 (ARMv7M), cr=00000000 CPU: PIPT / VIPT nonaliasing data cache, PIPT instruction cache OF: fdt: Machine model: NXP IMXRT1050-evk board ... This architecture does not have kernel memory protection. Run /init as init process [71] Jan 01 00:00:01 Running in background / # mmc0: new high speed SDHC card at address 0007 mmcblk0: mmc0:0007 SD8GB 7.42 GiB mmcblk0: p1 Micrel KSZ8081 or KSZ8091 402d8000.ethernet-1:02: attached PHY driver (mii_bus:phy_addr=402d8000.ethernet-1:02, irq=POLL) fec 402d8000.ethernet eth0: Link is Up - 100Mbps/Full - flow control off random: crng init done / # ps PID USER VSZ STAT COMMAND 1 root 872 S init 2 root 0 SW [kthreadd] 4 root 0 IW< [kworker/0:0H-kb] 5 root 0 IW [kworker/u2:0-ev] 6 root 0 IW< [mm_percpu_wq] 7 root 0 SW [ksoftirqd/0] 8 root 0 SW [kdevtmpfs] 9 root 0 IW< [inet_frag_wq] 10 root 0 IW< [writeback] 34 root 0 IW< [kblockd] 35 root 0 IW [kworker/0:1-pm] 36 root 0 IW< [rpciod] 37 root 0 IW< [kworker/u3:0] 38 root 0 IW< [xprtiod] 39 root 0 IW< [cfg80211] 40 root 0 SW [kswapd0] 41 root 0 IW [kworker/u2:1-ev] 42 root 0 IW< [nfsiod] 46 root 0 IW< [uas] 47 root 0 SW< [krfcommd] 48 root 0 IW< [sdhci] 49 root 0 SW [irq/37-mmc0] 51 root 0 IW< [ci_otg] 52 root 0 IW< [ci_power_lost] 54 root 0 IW< [ci_power_lost] 56 root 0 IW [kworker/0:3-eve] 71 root 728 S dropbear -R 73 root 884 S -/bin/hush 80 root 0 IW< [mmc_complete] 82 root 0 IW< [kworker/0:1H-ev] 96 root 0 IW [kworker/0:0-eve] 97 root 880 R ps

Here are some troubleshooting tips, in case tftpboot does not work for you from U-Boot:

  1. As trivial as it sounds make sure that the board is connected to the LAN with an Ethernet cable.
  2. Suppose you are still not getting your file from the TFTP server. It is possible that the problem is on the host side - you must set up a TFTP server correctly. Just google for "how to set up a tftp server" and follow the advice from some top articles.
  3. Make sure you have copied a file you are trying to download to the TFTP server directory on the host.
  4. Disable the firewall on the host since get enabled, it will block TFTP requests from the target.
  5. On the target, make sure that you have set ipaddr and serverip correctly. Check ethaddr and make sure that you don't have another embedded board (eg. another NXP i.MX RT1050 EVK board) configured for the same MAC address.