Build MicroBlaze Linux kernel

On the development host

This guide provides some step-by-step instructions on how to build a Microblaze Linux Kernel image for the FMC board connected to a:

• KC705

• KCU105

• VC707

• VCU118

• VCU128

The ADI Linux repository contains the Linux Kernel flavor from Analog Devices Inc. rootfs.cpio.gz contains the files system to be used. As the compiler, the Microblaze GNU Tools are bumbled on both AMD Vivado and AMD Vivis, as well as the xsdb tool for booting.

After ensuring all tools are installed, clone the ADI Linux repository

~$

git clone https://github.com/analogdevicesinc/linux.git \
            --no-single-branch --depth=10 \
            -- linux

The depth and no-single-branch options are included to speed up the cloning by fetching only near the head of each branch/release, you may remove them to fetch all history, but bear in mind it will go from around 800 MB to around 3.4GB and growing.

Checkout the Release branch

Tip

Use the latest release, if not required otherwise!

The release branches have the format <Year>_R[1|2], starting from 2014_R2.

~$

git checkout origin/2021_R1 -b 2021_R1

Branch 2021_R1 set up to track remote branch 2021_R1 from origin.
Switched to a new branch '2021_R1'

Setup cross compile environment variables

The Microblaze GNU Toolchain bumbled in AMD Vivado/Xilinx is the recommended compiler.

/data/opt/Xilinx/Vitis/$XVERSION/gnu/microblaze/linux_toolchain/lin64_le/bin/

~$

XVERSION=2024.2

~$

GCC_MICROBLAZE=$PATH_TO_XILINX/Vits/$VITIS_VERSION/gnu/microblaze/linux_toolchain/lin64_le/bin/

~$

export ARCH=microblaze

~$

export CROSS_COMPILE="$GCC_MICROBLAZE/microblazeel-xilinx-linux-gnu-"

Important

Find the path to the Xilinx installation folder, and then use it to replace this string: $PATH_TO_XILINX that is written above. Same goes for the $VITIS_VERSION, where you choose the Vitis version. Alternatively, you can replace Vitis with Vivado.

Compile the kernel

Prepare the configuration:

~/linux$

make adi_mb_defconfig

#
# configuration written to .config
#

Download the rootfs:

~/linux$

wget https://swdownloads.analog.com/cse/microblaze/rootfs/rootfs.cpio.gz

 Saving to: ‘rootfs.cpio.gz’
 rootfs.cpio.gz    100%[======================>]   4.74M  6.39MB/s    in 0.7s
 2025-05-28 11:00:09 (6.39 MB/s) - ‘rootfs.cpio.gz’ saved [4970267/4970267]

The result of building the kernel is an elf file in arch/microblaze/boot named simpleImage.<dts-file> based on the dts specified.

The build process for the kernel searches in the arch/microblaze/boot/dts directory for a specified device tree file and then builds the device tree into the kernel image.

The following command shows the general format for the build target name. Note that the <dts-file> does not include the file extension .dts.

~/linux$

make simpleImage.<dts-file>

To see what device-trees for the different FPGA carrier and FMC module combination exist type:

~/linux$

ls -l arch/microblaze/boot/dts

So, for example, for vcu118_quad_ad9081_204c_txmode_23_rxmode_25_onchip_pll_revc_nz1.dts:

~/linux$

make simpleImage.vcu118_quad_ad9081_204c_txmode_23_rxmode_25_onchip_pll_revc_nz1

  SYNC    include/config/auto.conf.cmd
  CC      scripts/mod/empty.o
  CC      scripts/mod/devicetable-offsets.s
  MKELF   scripts/mod/elfconfig.h
  HOSTCC  scripts/mod/modpost.o
  HOSTCC  scripts/mod/sumversion.o
  HOSTCC  scripts/mod/file2alias.o

[ --snip-- ]

  AR      init/built-in.a
  LD      vmlinux.o
  MODPOST vmlinux.symvers
  MODINFO modules.builtin.modinfo
  GEN     modules.builtin
  LD      .tmp_vmlinux.kallsyms1
  KSYMS   .tmp_vmlinux.kallsyms1.S
  AS      .tmp_vmlinux.kallsyms1.S
  LD      .tmp_vmlinux.kallsyms2
  KSYMS   .tmp_vmlinux.kallsyms2.S
  AS      .tmp_vmlinux.kallsyms2.S
  LD      vmlinux
  SORTTAB vmlinux
  SYSMAP  System.map
  OBJCOPY arch/microblaze/boot/simpleImage.vcu118_quad_ad9081_204c_txmode_23_rxmode_25_onchip_pll_revc_nz1
  SHIPPED arch/microblaze/boot/simpleImage.vcu118_quad_ad9081_204c_txmode_23_rxmode_25_onchip_pll_revc_nz1.unstrip
  STRIP   vmlinux arch/microblaze/boot/simpleImage.vcu118_quad_ad9081_204c_txmode_23_rxmode_25_onchip_pll_revc_nz1.strip
  UIMAGE  arch/microblaze/boot/simpleImage.vcu118_quad_ad9081_204c_txmode_23_rxmode_25_onchip_pll_revc_nz1.ub
Image Name:   Linux-5.10.0-97916-g513446e488c3
Created:      Tue Jan 18 12:07:35 2022
Image Type:   MicroBlaze Linux Kernel Image (uncompressed)
Data Size:    18398124 Bytes = 17966.92 KiB = 17.55 MiB
Load Address: 80000000
Entry Point:  80000000
Kernel: arch/microblaze/boot/simpleImage.vcu118_quad_ad9081_204c_txmode_23_rxmode_25_onchip_pll_revc_nz1 is ready  (#3678)

The STRIP image (.strip) found under arch/microblaze/boot is the ELF image to load via the debugger.

Boot on FPGA MicroBlaze

One method to load the kernel onto the already built and running FPGA which has the MicroBlaze processor is to use xsdb/xsct or xmd from the AMD Xilinx Vivado/Vitis toolset to download the build .strip file.

Go to the folder containing the .strip and system_top.bit file, to flash the bitstream and download the Image.

Note

The system_top.bit is obtained from the HDL project. Learn how to Build an HDL project, but instead of using the generated *.sdk/system_top.xsa, use the *.runs/impl_1/system_top.bit.

With xsdb/xsct:

xsdb> connect
xsdb> fpga -f system_top.bit
xsdb> targets
  1  xcku040
     2  MicroBlaze Debug Module at USER2
        3  MicroBlaze #0 (Running)
xsdb> targets 3
xsdb> dow simpleImage.kcu105_fmcdaq2
xsdb> con
xsdb> disconnect

To automate, the same commands can be added to a .tcl script and run with xsdb run.tcl.

With xmd:

xmd> fpga -f system_top.bit
xmd> connect mb mdm
xmd> dow simpleImage.vc707_fmcomms2-3
xmd> run