Xtensa simulator

Overview

The Xtensa processor architecture is a configurable, extensible, and synthesizable 32-bit RISC processor core. Processor and SOC vendors can select from various processor options and even create customized instructions in addition to a base ISA to tailor the processor for a particular application.

For more information, see https://ip.cadence.com/ipportfolio/tensilica-ip/xtensa-customizable

Hardware

The following Xtensa cores are officially supported:

sample_controller

System Clock

Xtensa cores can be configured to use either internal or external timers. The frequency of the clock under simulation is set to 25MHz.

System requirements

Prerequisites

A Linux host system is required for Xtensa development work. We recommend using a Debian 9.x (Stretch) or recent Ubuntu releases (with multilib support).

Only Xtensa tools version RF-2016.4-linux or later are officially supported. Other versions may work but are not supported by Cadence Systems Inc.

In order to set up the Zephyr OS build system, a Linux 32-bit GCC compiler must be installed on the building linux box. Install GCC if needed either by downloading Zephyr SDK or by using your distribution package manager.

On Debian/Ubuntu systems, you can install gcc-multilib package as follows:

#aptitude install gcc-multilib # Or what ever package manager (apt, apt-get, ...)

Set up build environment

We recommend you create a ~/.zephyrrc file, a shell script that shall be sourced each time before you start working on Zephyr. You can use the following code to create that file:

$ cat > ~/.zephyrrc
if test "${CROSS}" = xcc
then
    export ARCH=xtensa
    export BOARD=xt-sim
    export ZEPHYR_TOOLCHAIN_VARIANT=xcc
    export XTENSA_TOOLS_PATH=/opt/xtensa/XtDevTools/install/tools/RG-2016.4-linux/XtensaTools
    export XTENSA_BUILDS_PATH=/opt/xtensa/XtDevTools/install/builds/RG-2016.4-linux
    #export XTENSA_BUILD_DIR= #Keep empty to use default directory
    export EMU_PLATFORM=xt-run
elif test "${CROSS}" = zephyr-xtensa
then
    export ARCH=xtensa
    export BOARD=qemu
    export ZEPHYR_TOOLCHAIN_VARIANT=zephyr
    export ZEPHYR_SDK_INSTALL_DIR=/opt/xtensa/zephyr-sdk-64-INTERNAL-11-22-2016
elif test "${CROSS}" = zephyr-x86
then
    export ARCH=x86
    export BOARD=qemu_x86
    export ZEPHYR_TOOLCHAIN_VARIANT=zephyr
    export ZEPHYR_SDK_INSTALL_DIR=/opt/xtensa/zephyr-sdk-64-INTERNAL-11-22-2016
else
    echo "Unsupported compiler '${CROSS}' defined by environment variable CROSS"
fi

Once the ~/.zephyrrc file is created, you can start working. However, each time you start a new shell you will need to execute the following commands before you can compile anything:

$ cd path/to/zephyr # replace path/to by a real path
$ CROSS=xcc source zephyr-env.sh # Select xcc as compiler

Adding a user-defined Xtensa core

Add your own core to the list of supported cores as follows:

$ XTENSA_CORE=myCore
$ $(which echo) -e "config ${XTENSA_CORE}\n\tbool \"${XTENSA_CORE} core\"\n" >> "soc/xtensa/Kconfig.cores"

Create a folder for that core:

$ mkdir soc/xtensa/${XTENSA_CORE}

Create and copy to that folder a custom linker script (more on linker script in next section):

$ cp  linker.ld  soc/xtensa/${XTENSA_CORE}/linker.ld

Add a Makefile:

$ echo "obj-y = soc.o" > soc/xtensa/${XTENSA_CORE}/Makefile

Add Zephyr specific sections to the linker script. The file “soc/xtensa/linker_more.ld” contains Zephyr-specific linker sections that should be added to the default linker script linker.ld (inside SECTIONS region). If you are not using a linker script, you must create one and add these sections. The memory segment and PHDR should be replaced by appropriate values.

The linker script should be named linker.ld and placed in the directory soc/xtensa/${XTENSA_CORE}.

Configuring build

# From the root of the zephyr repository
west build -b None samples/hello_world
west build -t menuconfig

Below is an example of usage for typical configuration:

Select Architecture
1. Select Xtensa architecture
Select XTENSA core Selection
1. Select appropriate core (example hifi3_bd5 core)
Select XTENSA Options
1. Set Hardware clock cycles per second to appropriate value
2. Set The path to Xtensa tool to appropriate value
3. Set The version of Xtensa tool to appropriate version
4. Set Xtensa build directory to appropriate value
Select Board Selection
1. Select Xtensa Development ISS
Select Device Drivers
1. Uncheck Serial Drivers
Select Compile and Link Features
1. Set compiler configuration and build options correctly to project requirements
Hit Exit and confirm saving the changes.

You may need to change other options in menuconfig depending on his project specific needs.

Compiling and running

The Xtensa executable can be run in the simulator either with a standalone core, or with a core connected to simulated peripherals.

Build and run as follows:

west build -b None
west build -t run