1. Typical HPS Boot Flow
2. HPS customization and u-boot
3. Source code file structure for u-boot
4. Review custom u-boot recipe
5. Generate u-boot Custom Board source code based on the Quartus Handoff folder

Complex application class processors, such as the Cortex-A9 found in the Cyclone V SoC FPGA, require a bootloader to boot from reset.

The HPS boot flow includes the following stages:

1. Boot ROM
2. Preloader
3. U-Boot
4. Linux
5. Application

The following table presents a short description of the different boot stages:

For more information, please refer to HPS SoC Boot Guide - Cyclone V SoC Development Kit and Cyclone V Hard Processor System Technical Reference Manual (Booting and Configuration chapter).

ARM processors most commonly use u-boot as the bootloader of choice. u-boot is an open source bootloader and is available on github. The current version of u-boot includes the Preloader stage described in the section above.

The SoC FPGA HPS section is customized based on Platform Designer selections. This was described in the section Creating Processor System in the Custom SoC FPGA Workshop.

The section described below is derived from the Rocketboards Building Bootloader page

Quartus creates a hps_isw_handoff folder during compilation. This folder includes the HPS customization information that u-boot requires in order to build a bootloader for the custom board. These include

• HPS Peripheral selections and pin muxing
• HPS clock settings
• SDRAM selections

For Cyclone V SoC and Arria V SoC, the handoff information created by Quartus compilation comes in several formats: C source code, XML and binary files. bsp-editor takes this information and turns it into source code which is used to build u-boot. qts_filter, in turn, takes the handoff information and the output of bsp-editor and creates board specific c source code for u-boot.

The diagram below shows the typical u-boot build flow for Cyclone V SoC FPGAs. A later section will describe how to use the bsp-editor and qts_filter to create the two Source Code flow blocks. The rest of the u-boot build will be done by yocto using recipes created for this purpose.

It is useful to examine the file structure of u-boot. The reader will see which sections must be modified in order to add a new custom board. The following image shows the general directory structure of u-boot source code

There are five sections of u-boot that need additions or modifications in order to support a new custom board. The snapshots below use the pre-installed sockit board as an example.

1. board folder
2. arch/arm/dts folder
3. configs folder
4. include/configs folder
5. arch/arm/mach-socfpga folder

The qts sub folder contains the four source code files generated by the qts_filter utility based on the Quartus handoff folder files and bsp-editor utility output files. The MAINTAINERS file is edited to be specific for this board and references maintained files that customize u-boot. The Yocto u-boot recipe for the custom board will need to create a new custom board folder and populate it with the appropriate files.

u-boot reads a board specific devicetree at boot time to customize its boot process. A board can have both a dts source file and a dtsi include file. The example for the sockit board indicates this. The reader will need to create new custom dts and dtsi devicetree files for the custom board. The Makefile includes all the available board devicetree compiler build options. The reader will need to modify this file to support the new custom board. The Yocto u-boot recipe for the custom board will need to copy the modified Makefile and the created dts & dtsi files to the arch/arm/dts folder.

This folder contains build configurations for all the boards supported by u-boot. The image above shows the build configuration defconfig file for the sockit board. Recall that the MACHINE configuration file selects the specific u-boot build configuration defconfig for the Yocto build with its UBOOT_CONFIG variable. The reader will need to create a new defconfig file specifically for the custom board. The Yocto u-boot recipe for the custom board will need to copy the created defconfig file to the configs folder.

This folder contains a header file required to provide custom board features necessary for the u-boot build. It specifically provides the size of the physical DRAM on the board and the Linux load address in DRAM. The reader will need to provide a custom version of this file to support a new custom board. The Yocto u-boot recipe for the custom board will need to copy the created header file to the include/configs folder.

This folder contains a Kconfig file. This provides additional build configurations for u-boot socfpga based machines. The reader will need to modify this file to support a new custom board. The Yocto u-boot recipe for the custom board will need to copy the modified Kconfig file to the arch/arm/mach-socfpga folder.

Open the file socfpga_yocto_workshop/poky/meta-my-custom-soc-board/recipes-bsp/u-boot/u-boot-socfpga_v2021.04.bb in the default editor, gedit.

The files sub-directory referenced in the recipe above, contains all the created or modified files necessary to facilitate building u-boot for the custom board. The reader will review the files identifying necessary additions or modifications. The u-boot scripts declares the files in the local files sub-directory. It creates a qts folder in the u-boot source directory. Lastly it copies the files to their respective directories in the u-boot source folder.

Note: None of these files were created. Copies were made of their sockit board equivalents and modified accordingly.

DE10-nano

    $ cd ~/socfpga-workshop/socfpga_yocto_workshop/poky/meta-my-custom-soc-board/recipes-bsp/u-boot/files/

    $ cp socfpga_cyclone5_de10nano.dts socfpga_cyclone5_my_custom_soc_board.dts

    $ cp socfpga_cyclone5_de10nano-u-boot.dtsi socfpga_cyclone5_my_custom_soc_board-u-boot.dtsi

DataStorm DAQ

    $ cd ~/socfpga-workshop/socfpga_yocto_workshop/poky/meta-my-custom-soc-board/recipes-bsp/u-boot/files/

    $ cp socfpga_cyclone5_datastormdaq.dts socfpga_cyclone5_my_custom_soc_board.dts

    $ cp socfpga_cyclone5_datastormdaq-u-boot.dtsi socfpga_cyclone5_my_custom_soc_board-u-boot.dtsi

SoCKit

    $ cd ~/socfpga-workshop/socfpga_yocto_workshop/poky/meta-my-custom-soc-board/recipes-bsp/u-boot/files/

    $ cp socfpga_cyclone5_sockit.dts socfpga_cyclone5_my_custom_soc_board.dts

    $ cp socfpga_cyclone5_sockit-u-boot.dtsi socfpga_cyclone5_my_custom_soc_board-u-boot.dtsi

DE10-nano

    $ cp socfpga_de10nano_defconfig socfpga_my_custom_soc_board_defconfig

DataStorm DAQ

    $ cp socfpga_datastormdaq_defconfig socfpga_my_custom_soc_board_defconfig

SoCKit

    $ cp socfpga_sockit_defconfig socfpga_my_custom_soc_board_defconfig

The following steps guide the reader to create the custom source files for the /board/custom/my-custom-soc-board/qts u-boot folder.

Open an Embedded shell. Source the embedded_command_shell script

    $ ~/intelFPGA_lite/20.1/embedded/embedded_command_shell.sh

DE10-nano

    $ cd ~/socfpga-workshop/socfpga_hw_workshop/de10nano_ghrd/

    $ mkdir -p software/bootloader

DataStorm DAQ

    $ cd ~/socfpga-workshop/socfpga_hw_workshop/datastormdaq_ghrd/

    $ mkdir -p software/bootloader

SoCKit

    $ cd ~/socfpga-workshop/socfpga_hw_workshop/sockit_ghrd/

    $ mkdir -p software/bootloader

Run bsp-create-settings with no user options to convert the handoff data into source code

DE10-nano

    $ bsp-create-settings --type spl --bsp-dir software/bootloader --preloader-settings-dir "hps_isw_handoff/de10nano_ghrd_hps_0" --settings software/bootloader/settings.bsp

DataStorm DAQ

    $ bsp-create-settings --type spl --bsp-dir software/bootloader --preloader-settings-dir "hps_isw_handoff/datastormdaq_ghrd_hps_0" --settings software/bootloader/settings.bsp

SoCKit

    $ bsp-create-settings --type spl --bsp-dir software/bootloader --preloader-settings-dir "hps_isw_handoff/sockit_ghrd_hps_0" --settings software/bootloader/settings.bsp

    $ cd software/bootloader

    $ git clone -b socfpga_v2021.04 https://github.com/arrow-socfpga/u-boot-socfpga

    $ cd u-boot-socfpga

Run the qts_filter to take the sources from the handoff folder and the ones generated by bsp-create-settings, format them appropriately, and copy them to the u-boot qts source code folder in the custom layer.

    $ ./arch/arm/mach-socfpga/qts-filter.sh cyclone5  ../../../ ../  ~/socfpga-workshop/socfpga_yocto_workshop/poky/meta-my-custom-soc-board/recipes-bsp/u-boot/files/my-custom-soc-board/qts/

Next - Review the Linux Kernel recipe

Return to - Review FPGA configuration recipe