payload_uboot.md 1.6 KB

U-Boot as a payload to OpenSBI

U-Boot is an open-source primary boot loader. It can be used as first and/or second stage boot loader in an embedded environment. In the context of OpenSBI, U-Boot can be specified as a payload to the OpenSBI firmware, becoming the boot stage following the OpenSBI firmware execution.

The current stable upstream code of U-Boot does not yet include all patches necessary to fully support OpenSBI. To use U-Boot as an OpenSBI payload, the following out-of-tree patch series must be applied to the upstream U-Boot source code:

HiFive Unleashed support for U-Boot

https://lists.denx.de/pipermail/u-boot/2019-February/358058.html

This patch series enables a single CPU to execute U-Boot. As a result, the next stage boot code such as a Linux kernel can also only execute on a single CPU. U-Boot SMP support for RISC-V can be enabled with the following additional patches:

https://lists.denx.de/pipermail/u-boot/2019-February/358393.html

Building and Generating U-Boot images

Please refer to the U-Boot build documentation for detailed instructions on how to build U-Boot images.

Once U-Boot images are built, the Linux kernel image needs to be converted into a format that U-Boot understands:

<uboot-dir>/tools/mkimage -A riscv -O linux -T kernel -C none -a 0x80200000 -e 0x80200000 -n Linux -d \
		<linux_build_directory>arch/riscv/boot/Image \
		<linux_build_directory>/arch/riscv/boot/uImage

Copy the uImage to your tftpboot server path if network boot is required.