This how-to describes how to build the u-boot bootloader for your target platform. Building the U-Boot bootloader is a part of the Xilinx design flow described in Xilinx Open Source Linux. U-Boot depends upon an externally build device tree compiler (dtc) in order to build successfully. Please build the dtc tool before proceeding with the steps described below.

• Install Xilinx tools
• Fetch Sources
• Build Device Tree Compiler

Tools Required

• Xilinx SDK

Input Files Required

• config.mk (MicroBlaze only)
• xparameters.h (MicroBlaze only)

Output Files Produced

• u-boot
• mkimage

U-boot build steps

All commands have to be executed in your u-boot source directory.

Zynq:

As an example to build U-Boot for ZC702 execute:

As an example to buildU-Boot for ZCU102 execute:

Configuring U-Boot (>= 2020.1 Release)

After the build process completes the target u-boot elf-file is created in the top level source directory, named u-boot/u-boot.elf. Additionally in the tools/ directory the mkimage utility is created, which is used in other tasks to wrap images into u-boot format.

make distclean
make xilinx_zynq_virt_defconfig
export DEVICE_TREE="zynq-zc702"
make

To build U-boot for ZCU102 rev1.0 board, follow below steps.

make distclean
make xilinx_zynqmp_virt_defconfig
export DEVICE_TREE="zynqmp-zcu102-rev1.0"
make

To make mkimage available in other steps, it is recommended to add the tools directory to your $PATH.

U-Boot for MicroBlaze

The Xilinx U-Boot project is based on the source code from git:git.denx.de

The devices that have been tested include UART lite, UART 16550, Linear flash, EMAC lite, LL TEMAC with PLB DMA, and AXI EMAC with AXI DMA. The timer counter and interrupt controller were also tested.
Tests were done on Spartan 605 (PLB and AXI) and Kintex 705 (AXI) evaluation platforms using XPS 14.2 and 14.3.

The hardware project

Typical
Make sure the following peripherals are included in the system:

Optional
U-Boot includes capabilities of writing to/reading from flash and also transferring files over a network if the available hardware is present:
Additional peripherals and features are considered outside the scope of this page.

Building U-Boot

There are two ways to compile u-boot for Microblaze board.
1. OSL flow to compile u-boot
The U-Boot source tree can be downloaded from the Xilinx Git server. The repository is u-boot-xlnx and the branch is master:
The U-Boot compilation will use the definitions and flags defined in config.mk and xparameters.h . Import these two files generated by the petalinux project into the U-Boot directory for MicroBlaze
Rename platform-auto.h to microblaze-generic.h
After renaming, copy microblaze-generic.h to the u-boot-xlnx/include/configs
Replace the dts file of u-boot-xlnx via petalinux project
Renamed this generated dts file to microblaze-generic.dts and copy it to the u-boot-xlnx
Go into the u-boot-xilinx top directory and run the following commands in bash to compile the u-boot

Loading and running U-Boot

Downloading U-Boot to MicroBlaze
Once the bitstream containing at least a minimally configured hardware system has been downloaded to the FPGA, XMD is used to download the cross-compiled U-Boot to the MicroBlaze soft processor:
U-Boot commands
The list of U-boot commands can be accessed while in the U-Boot prompt. Type "help" or "?" for a complete listing of available commands.

Documentation on U-Boot may be found at http://www.denx.de/wiki/DULG/Manual .

Running Linux using U-Boot

Preparing the Linux images for U-Boot
Specific details on building the kernel for MicroBlaze are contained in the Build Kernel page.
Instructions to obtain a root filesystem can be found at the Build and Modify a Root File System page.

The kernel and the root filesystem must be wrapped with a U-Boot header in order for U-Boot to accept these files. The mkimage utility is used for this purpose, however, it is not part of the MicroBlaze GNU tools. It is part of U-Boot itself and if U-Boot has been compiled as specified on this page, it will be found under <u-boot-xlnx>/build/tools/ .

When building linux.bin, as explained in the Build Kernel page, the kernel build process automatically creates an additional image, with the ".ub" suffix. linux.bin.ub is the Linux binary image wrapped with a U-Boot header. The Linux compilation process will automatically invoke mkimage, therefore, it is important to include the path to the U-Boot tools in the PATH environment variable.

The root filesystem also needs to be wrapped with a U-Boot header as follows:

Booting Linux
XMD or TFTP may be used to download Linux to the FPGA (memory). U-Boot can then use these files to boot Linux. Once the kernel, root filesystem, and device tree images are present in memory, the command to boot Linux is:

Note: Make sure the kernel and root filesystem images are wrapped by with the U-Boot header. The device tree blob does not need to be wrapped with the U-Boot header.

Creating the BSP required by U-Boot (Unverified)
This is old BSP and doesn't tested with latest u-boot.
To build U-Boot correctly, some information about the system will need to be provided to the U-Boot build tree. This information is generated by the U-Boot BSP.

First, download the U-Boot BSP source Once it has been installed and the project has been exported to SDK, the U-Boot BSP can be created for the system.

In order for the U-Boot BSP to generate the necessary settings for U-Boot, it needs to know which specific peripherals should be used for some corresponding tasks. These selections are made in the fields/drop-down menus located in the 'Settings' of the newly created U-Boot BSP. For example:
Once the U-Boot BSP has been compiled in SDK, the generated files, config.mk and xparameters.h, can be found at <sdk_workspace>/uboot_bsp_0/microblaze_0/libsrc/uboot_v*/ .

Downloading the source tree
The U-Boot source tree can be downloaded from the Xilinx Git server. The repository is u-boot-xlnx and the branch is master:
Compiling U-Boot
The U-Boot compilation will use the definitions and flags defined in config.mk and xparameters.h . Import these two files generated by the U-Boot BSP in SDK into the U-Boot directory for MicroBlaze located at <u-boot-xlnx>/board/xilinx/microblaze-generic/ .

linux-host> cd <u-boot-xlnx>
linux-host> export BUILD_DIR=$PWD/build
linux-host> make microblaze-generic_defconfig
linux-host> make

Build Steps

• Fetch Sources
• Build FSBL
• Build Device Tree Compiler (DTC)
• Build PMU Firmware
• Build Arm Trusted Firmware (ATF)
• (You are here) Build U-Boot
• Build and Modify a Root File System
• Build Device Tree Blob
• Build Linux Kernel
• Prepare Boot Image
• Prepare Boot Medium
• Setup a Serial Console
• Additional Information: Build Qt and Qwt Libraries

Related Links

• Zynq U-boot
• PowerPC U-boot
• Boot Zynq UltraScale+ MPSoC via JTAG