How to boot the kernel via TFTP from U-Boot

Revision as of 15:43, 10 September 2019 by Registered User
This message will disappear after all relevant tasks have been resolved.
Semantic MediaWiki
There are 1 incomplete or pending task to finish installation of Semantic MediaWiki. An administrator or user with sufficient rights can complete it. This should be done before adding new data to avoid inconsistencies.

Template:ArticleMainWriter Template:ArticleApprovedVersion


This page explains how to boot the Linux kernel from U-Boot through a TFTP server (trivial file transfer protocol[1]) installed on a host PC, based on the U-Boot command pxe.

1. Documentation[edit source]

The documentation is available in the U-Boot source:

2. tftp server installation on host PC[edit source]

See: https://importgeek.wordpress.com/2013/09/04/install-configure-and-test-tftp-server-in-ubuntu/

3. tftp server configuration[edit source]

U-Boot follows pxelinux's rules[2] to download from the tftp server a #PXE configuration file located in the #pxelinux.cfg directory.
See details in http://syslinux.zytor.com/wiki/index.php/PXELINUX

U-Boot pxe command loads and parses a #PXE configuration file in #pxelinux.cfg directory of the tftp server.

3.1. PXE configuration file[edit source]

Each PXE configuration file has same format as the extlinux.conf file generated by yocto distribution.

In this file, you define the kernel and the device tree loaded by tftp (KERNEL and FDT option) and the Linux bootarg used to start the kernel (APPEND option) with the rootfs to use.

This rootfs can be on a device (e•MMC, SDCard, NAND, and so on).

For example for an ev1 board, with the rootfs in the 6th partition of the SD card (/dev/mmcblk0p6) we have the file: 

 menu title Select the boot mode
 DEFAULT sdcard
 LABEL sdcard
 	KERNEL uImage
 	FDT stm32mp157c-ev1.dtb
 	APPEND root=/dev/mmcblk0p6 rootwait rw earlyprintk console=ttySTM0,115200

To fully boot on a network (kernel and rootfs), you can define the rootfs as

  • ramfs [3] with INITRD tag in configuration file.
    The inird need to be generated [4]
  • nfs [5] with the bootargs (APPEND: rootfstype=nfs nfsroot=... [6]) and nfs server [7].

You be can add several choice by adding other labels and TIMEOUT (selection needs user action on the U-Boot console); for example: 

menu title Select the boot mode
DEFAULT ramfs
TIMEOUT 20
LABEL ramfs
	KERNEL uImage
	FDT stm32mp157c-ev1.dtb
	INITRD uInitrd
	APPEND rootwait rw earlyprintk console=ttySTM0,115200
LABEL sdcard
	KERNEL uImage
	FDT stm32mp157c-ev1.dtb
	APPEND root=/dev/mmcblk0p6 rootwait rw earlyprintk console=ttySTM0,115200
LABEL eMMC
	KERNEL uImage
	FDT stm32mp157c-ev1.dtb
	APPEND root=/dev/mmcblk1p6 rootwait rw earlyprintk console=ttySTM0,115200

3.2. pxelinux.cfg directory[edit source]

Because more than one board may be booted from the same server, the PXE configuration file name depends on U-boot parameters (hardware address/IP address).
U-Boot looks in the pxelinux.cfg directory for a PXE configuration file name in this order:

  1. UUID comes from "pxeuuid" variable [8]
  2. hardware type and address: Ethernet (ARP[9] type "1") with MAC address[10] (ethaddr env variable)
  3. IP address of the board and each subnet mask
  4. at the end, the file named "default-$CONFIG_SYS_ARCH-$CONFIG_SYS_SOC"

You need to provide at least one file on the server for your board.

Each file of the pxelinux.cfg directory can share the the same content (or can be a symbolic link to a default one).

For example, for an stm32mp1 target, when:

  • UUID is not defined
  • ethaddr=00:80:e1:01:2d:6f
  • IP =10.48.0.141 (hexa coding=0A30008D)
  • ARCH=arm and SOC=stm32mp

U-Boot searches the configuration file is this order:

  1. "01-00-80-e1-01-2d-6f"
  2. 0A30008D then subnet 0A30008, 0A3000, 0A300 ...
  3. default-arm-stm32mp


With ethaddr=00:80:e1:01:2d:6f, the tftp directory (for example /tftpboot) may look like: 

 ├── pxelinux.cfg                   directory
 │   ├── 01-00-80-e1-01-2d-6f       configuration file for MAC address 00:80:e1:01:2d:6f
 ├── stm32mp157c-ev1.dtb            device tree
 ├── uImage                         kernel

An other example with

  • different boards (identified by a MAC address)
    each pxe file selects a different device tree (ed1, ev1, dk1, dk2) or kernel file
  • fallback with the IP address submask (symbolic link to default-arm-stm32mp)
  • default-arm-stm32mp (final fallbackup file)
 ├── pxelinux.cfg
 │   ├── 01-00-80-e1-01-2d-6f            configuration file for MAC address 00:80:e1:01:2d:6f
 │   ├── 01-00-80-e1-42-42-8c            configuration file for MAC address 00:80:e1:42:42:8c
 │   ├── 01-00-80-e1-42-42-cd            configuration file for MAC address 00:80:e1:42:42:cd
 │   ├── 01-00-80-e1-42-46-76            configuration file for MAC address 00:80:e1:42:46:6f
 │   ├── 0A300 -> default-arm-stm32mp    configuration file for IP address 10.48.0*.**
 │   ├── 0A30001 -> default-arm-stm32mp  configuration file for IP address 10.48.00.1*
 │   ├── 0A30004 -> default-arm-stm32mp  configuration file for IP address 10.48.00.4*
 │   ├── 0A30008 -> default-arm-stm32mp  configuration file for IP address 10.48.00.8*
 │   └── default-arm-stm32mp             default configuration file
 ├── stm32mp157c-ed1.dtb
 ├── stm32mp157c-ev1.dtb
 ├── stm32mp157a-dk1.dtb
 ├── stm32mp157c-dk2.dtb
 ├── uImage
 ├── uInitrd

4. Board command in U-boot console[edit source]

You can execute the DISTRO bootcmd for PXE: 

  env set serverip <you PC address>
  run bootcmd_pxe

5. Example[edit source]

Server address is 10.201.21.107 and directory of tftp is : 

 ├── pxelinux.cfg
 │   ├── 01-00-80-e1-01-60-da
 ├── stm32mp157c-ev1.dtb 
 ├── uImage

'01-00-80-e1-01-60-da' is the text file : 

menu title Select the boot mode
DEFAULT sdcard
LABEL sdcard
	KERNEL uImage
	FDT stm32mp157c-ev1.dtb
	APPEND root=/dev/mmcblk0p6 rootwait rw earlyprintk console=ttySTM0,115200

In the U-Boot console: 

STM32MP> env set serverip 10.201.21.107                      {{Highlight|set the server address}}
STM32MP> run bootcmd_pxe                                            {{Highlight|execute the DISTRO command}}
BOOTP broadcast 1
DHCP client bound to address 10.48.1.229 (19 ms)
missing environment variable: pxeuuid
missing environment variable: bootfile
Retrieving file: pxelinux.cfg/01-00-80-e1-01-60-da
Using ethernet@5800a000 device
TFTP from server 10.201.21.107; our IP address is 10.48.1.229; sending through gateway 10.48.3.254
Filename 'pxelinux.cfg/01-00-80-e1-01-60-da'.
Load address: 0xc4200000
Loading: #
	 105.5 KiB/s
done
Bytes transferred = 435 (1b3 hex)
Config file found
Select the boot mode
1:	sdcard
Enter choice: 1:	sdcard
missing environment variable: bootfile
Retrieving file: uImage
Using ethernet@5800a000 device
TFTP from server 10.201.21.107; our IP address is 10.48.1.229; sending through gateway 10.48.3.254
Filename 'uImage'.
Load address: 0xc2000000
Loading: #################################################################
	 #################################################################
	 #################################################################
	 #################################################################
	 #################################################################
	 #################################################################
	 #################################################################
	 #################################################################
	 #################################################################
	 #################################################################
	 #################################################################
	 #################################################################
	 #################################################################
	 #################################################################
	 #################################################################
	 #################################################################
	 #################################################################
	 ################
	 785.2 KiB/s
done
Bytes transferred = 5734976 (578240 hex)
append: root=/dev/mmcblk0p6 rootwait rw earlyprintk console=ttySTM0,115200
missing environment variable: bootfile
Retrieving file: stm32mp157c-ev1.dtb
Using ethernet@5800a000 device
TFTP from server 10.201.21.107; our IP address is 10.48.1.229; sending through gateway 10.48.3.254
Filename 'stm32mp157c-ev1.dtb'.
Load address: 0xc4000000
Loading: ############################
	 646.5 KiB/s
done
Bytes transferred = 138450 (21cd2 hex)
## Booting kernel from Legacy Image at c2000000 ...
   Image Name:   Linux-4.19.49
   Created:      2019-09-04  11:20:19 UTC
   Image Type:   ARM Linux Kernel Image (uncompressed)
   Data Size:    5734912 Bytes = 5.5 MiB
   Load Address: c2000040
   Entry Point:  c2000040
   Verifying Checksum ... OK
## Flattened Device Tree blob at c4000000
   Booting using the fdt blob at 0xc4000000
   XIP Kernel Image ... OK
   Using Device Tree in place at c4000000, end c4024cd1
SF: Detected mx66l51235l with page size 256 Bytes, erase size 64 KiB, total 64 MiB

Starting kernel ...

[    0.000000] Booting Linux on physical CPU 0x0
....
[    0.000000] Kernel command line: root=/dev/mmcblk0p6 rootwait rw earlyprintk console=ttySTM0,115200
....


6. References[edit source]

  1. ↑ https://en.wikipedia.org/wiki/Trivial_File_Transfer_Protocol
  2. ↑ https://en.wikipedia.org/wiki/Preboot_Execution_Environment
  3. ↑ https://en.wikipedia.org/wiki/Initial_ramdisk
  4. ↑ http://git.yoctoproject.org/cgit.cgi/poky/plain/meta/recipes-core/images/core-image-minimal-initramfs.bb
  5. ↑ https://en.wikipedia.org/wiki/Network_File_System
  6. ↑ https://www.kernel.org/doc/Documentation/filesystems/nfs/nfsroot.txt
  7. ↑ https://elinux.org/TFTP_Boot_and_NFS_Root_Filesystems
  8. ↑ https://en.wikipedia.org/wiki/Universally_unique_identifier
  9. ↑ https://en.wikipedia.org/wiki/Address_Resolution_Protocol
  10. ↑ https://en.wikipedia.org/wiki/MAC_address

Linux® is a registered trademark of Linus Torvalds.

Das U-Boot -- the Universal Boot Loader (see U-Boot_overview)

MultimediaCard

SD memory card (https://www.sdcard.org)

former spelling for e•MMC ('e' in italic)

Protocol used by the Internet Protocol, specifically IPv4, to map IP network addresses to the hardware addresses used by a data link protocol (https://en.wikipedia.org/wiki/Address_Resolution_Protocol)

media access control address (https://en.wikipedia.org/wiki/MAC_address)

Dynamic Host Configuration Protocol (See https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol for more details)

Execute In Place. Method of executing programs directly from long term storage rather than copying it into RAM (linked to NOR Flash).

Central processing unit

Retrieved from "https://wiki.st.com/stm32mpu-ecosystem-v3/index.php?title=How_to_boot_the_kernel_via_TFTP_from_U-Boot&oldid=60084"