A Handy U-Boot Trick

Bharath Bhushan Lohray — Mon, 16 Dec 2013 21:33:18 +0000

Embedded developers working on kernels or bare-metal programs often go through several development cycles. Each time the developer modifies the code, the code has to be compiled, the ELF (Executable and Linkable Format)/kernel image has to be copied onto the SD card, and the card then has to be transferred from the PC to the development board and rebooted. In my experience as a developer, I found the last two steps to be a major bottleneck. Even copying files to the fastest SD cards is slower than copying files between hard drives and sometimes between computers across the network.

Moreover, by frequently inserting and removing the SD card from the slot, one incurs the risk of damaging the fragile connectors on the development boards. Believe me! I lost a BeagleBoard by accidentally applying too much force while holding the board and pulling out the SD card. The pressure caused the I²C bus to fail. Because the power management chip was controlled by I²C, nothing other than the serial terminal worked after that. Setting aside the cost of the board, a board failure at a critical time during a project is catastrophic if you do not have a backup board.

After losing the BeagleBoard, I hit upon the idea to load my bare-metal code over the LAN via bootp and TFTP and leave the board untouched. This not only reduced the risk of mechanically damaging my board, but it also improved on my turn-around times. I no longer needed to copy files to the SD card and move it around.

In this article, I present a brief introduction to U-Boot and then describe the necessary configurations to set up a development environment using DHCP and TFTP. The setup I present here will let you deploy and test new builds quickly with no more than rebooting the board. I use the BeagleBone Black as the target platform and Ubuntu as the development platform for my examples in this article. You may, however, use the methods presented here to work with any board that uses U-Boot or Barebox as its stage-2 bootloader.

U-Boot

U-Boot is a popular bootloader used by many development platforms. It supports multiple architectures including ARM, MIPS, AVR32, Nios, Microblaze, 68K and x86. U-Boot has support for several filesystems as well, including FAT32, ext2, ext3, ext4 and Cramfs built in to it. It also has a shell where it interactively can take input from users, and it supports scripting. It is distributed under the GPLv2 license. U-Boot is a stage-2 bootloader.

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