Linux Porting On Xtensa Processors

These instructions explain how I build the toolchain, root filesystem and kernel for Linux running on an Xtensa ISS. Most of these works follow the guide from the official Linux Xtensa porting document.
Host environment

  • Ubuntu 8.04 LTS
  • gcc version 4.2.4

Download buildroot and the Linux kernel

This porting work uses snapshots tar ball from official Linux Xtensa website linux-xtensa-20080711.tar.gz. I have unzipped the source code and make the top directory as the <workdir>.

tar -zxvf linux-xtensa-20080711.tar.gz


Install any required processor specific overlay

This step is required because I am targeting a custom Xtensa processor.

cd <workdir>
./buildroot/target/xtensa/xt-buildroot-overlay-install \
    -t <HOME>/xtensa_RB-2008.4/XtDevTools/install/builds/RB-2008.4-linux/linuxcpu/src/xtensa-config-overlay.tar.gz \
    -b ./buildroot -k ./linux -c linuxcpu -l "Xtensa core for Linux"

Build a toolchain and root filesystem using buildroot

Configure buildroot

$ cd <workdir>/buildroot
$ ./target/xtensa/setup-config linuxcpu

Build buildroot

$ make

Build and Run a Linux Kernel on the Instruction Set Simulator (ISS)

Configure and Build the Kernel for ISS

$ export PATH="<workdir>/buildroot/build_xtensa_linuxcpu/staging_dir/usr/bin:$PATH"

$ mkdir build-iss
$ cd linux
$ make O=../build-iss ARCH=xtensa KBUILD_DEFCONFIG=iss_defconfig defconfig

Also, when running menuconfig:

$ make O=../build-iss ARCH=xtensa  menuconfig

Under General setup, make sure the Initial RAM filesystem and RAM disk (initramfs/initrd) support entry is enabled. Underneath that, edit Initramfs source file(s), and enter the path to the cpio formatted root filesystem generated by buildroot:

Under Bus Options, deselect PCI support. Under Platform Options, deselect Default bootloader kernel arguments.
You need also select: Processor type and features -> Xtensa Processor Configuration (Custom Xtensa processor configuration) -> (X) Custom Xtensa processor configuration
After you select this flag, please make sure that <workdir>/linux/include/asm-xtensa/variant-linuxcpu/ exists.
Put the linuxcpu as the correct core name. These files are important for following kernel compilation.

Compile the kernel

Compile the linux kernel for your xtensa platform.

$ make O=../build-iss ARCH=xtensa CROSS_COMPILE=xtensa_linuxcpu-linux-uclibc-

Run the Kernel on ISS

$ xt-gdb <workdir>/build-iss/arch/xtensa/boot/Image.elf
(xt-gdb) target sim --turbo
(xt-gdb) symbol-file <workdir>/build-iss/vmlinux
(xt-gdb) run

Problems and errors

( XTCORE::bcopyToHost ) *WARNING* no translation available for virtual address 20004000 at ring 1

This line appears time to time. Though it does not stop the execution, there are something wrong with this porting work.
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