.. _boards-mtk_adsp:

Mediatek Audio DSPs
###################

Zephyr can be built and run on the Audio DSPs included in various
members of the Mediatek MT8xxx series of ARM SOCs used in Chromebooks
from various manufacturers.

Two of these DSPs are in the market already, implemented via the
MT8195 ("Kompanio 1380") and MT8186 ("Kompanio 520") SOCs.
Development has been done on and validation performed on at least
these devices, though more exist:

  ======  =============  ===================================  =================
  SOC     Product Name   Example Device                       ChromeOS Codename
  ======  =============  ===================================  =================
  MT8195  Kompanio 1380  HP Chromebook x360 13b               dojo
  MT8186  Kompanio 520   Lenovo 300e Yoga Chromebook Gen 4    steelix
  ======  =============  ===================================  =================

Hardware
********

These devices are Xtensa DSP cores, very similar to the Intel ADSP
series in concept (with the notable difference that these are all
single-core devices, no parallel SMP is available, but at the same
time there are fewer worries about the incoherent cache).

Their memory space is split between dedicated, fast SRAM and ~16MB of
much slower system DRAM.  Zephyr currently loads and links into the
DRAM area, a convention it inherits from SOF (these devices have
comparatively large caches which are used for all accesses, unlike
with intel_adsp).  SRAM is used for interrupt vectors and stacks,
currently.

There is comparatively little on-device hardware.  The architecture is
that interaction with the off-chip audio hardware (e.g. I2S codecs,
DMIC inputs, etc...) is managed by the host kernel.  The DSP receives
its data via a single array of custom DMA controllers.

Beyond that the Zephyr-visible hardware is limited to a bounty of
timer devices (of which Zephyr uses two), and a "mailbox"
bidirectional interrupt source it uses to communicate with the host
kernel.

Programming and Debugging
*************************

These devices work entirely in RAM, so there is no "flash" process as
such.  Their memory state is initialized by the host Linux
environment.  This process works under the control of a
``mtk_adsp_load.py`` python script, which has no dependencies outside
the standard library and can be run (as root, of course) on any
reasonably compatible Linux environment with a Python 3.8 or later
interpreter.  A chromebook in development mode with the dev packages
installed works great.  See the ChromiumOS developer library for more
detail:

* `Developer mode <https://www.chromium.org/chromium-os/developer-library/guides/device/developer-mode/>`__
* `Dev-Install: Installing Developer and Test packages onto a Chrome OS device <https://www.chromium.org/chromium-os/developer-library/guides/device/install-software-on-base-images/>`__

Once you have the device set up, the process is as simple as copying
the ``zephyr.img`` file from the build directory to the device
(typically via ssh) and running it with the script.  For example for
my mt8186 device named "steelix":

.. code-block:: console

   user@dev_host:~$ west build -b mt8186//adsp samples/hello_world
   ...
   ... # build output
   ...
   user@dev_host:~$ scp build/zephyr/zephyr.img root@steelix:
   user@dev_host:~$ scp soc/mediatek/mt8xxx/mtk_adsp_load.py root@steelix:
   user@dev_host:~$ ssh steelix

   root@steelix:~ # ./mtk_adsp_load.py load zephyr.img
   *** Booting Zephyr OS build v3.6.0-5820-gd2a89b3c089e ***
   Hello World! mt8186_adsp/mt8186_adsp

Debugging
=========

Given the limited I/O facilities, debugging support remains limited on
these platforms.  Users with access to hardware-level debug and trace
tools (e.g. from Cadence) will be able to use them as-is.  Zephyr
debugging itself is limited to printk/logging techniques at the
moment.  In theory a bidirectional console like winstream can be used
with gdb_stub, which has support on Xtensa and via the SDK debuggers,
but this is still unintegrated.

Toolchains
**********

The MT8195 toolchain is already part of the Zephyr SDK, so builds for
the ``mt8195//adsp`` board should work out of the box simply following
the generic Zephyr build instructions in the Getting Started guide.

The MT8186 toolchain is not, and given the proliferation of Xtensa
toolchains in the SDK may not be.  The overlay files for the device
are maintained by the SOF project, however, and building a toolchain
yourself using crosstools-ng is not difficult or time-consuming.  This
script should work for most users:

.. code-block:: shell

   #!/bin/sh

   TC=mtk_mt818x_adsp

   # Grab source (these are small)
   git clone https://github.com/crosstool-ng/crosstool-ng
   git clone https://github.com/thesofproject/xtensa-overlay

   # Build ct-ng itself
   cd crosstool-ng
   ./bootstrap
   ./configure --enable-local
   make -j$(nproc)

   mkdir overlays
   (cd overlays; ln -s ../../xtensa-overlay/xtensa_mt8186.tar.gz xtensa_${TC}.tar.gz)

   # Construct a .config file
   cat >.config <<EOF
   CT_CONFIG_VERSION="3"
   CT_EXPERIMENTAL=y
   CT_OVERLAY_LOCATION="overlays"
   CT_OVERLAY_NAME="${TC}"
   CT_ARCH_XTENSA=y
   CT_XTENSA_CUSTOM=y
   CT_TARGET_VENDOR="${TC}_zephyr"
   CT_TARGET_CFLAGS="-ftls-model=local-exec"
   CT_CC_GCC_CONFIG_TLS=n
   CT_GDB_CROSS_EXTRA_CONFIG_ARRAY="--enable-xtensa-use-target-regnum --disable-xtensa-remote-g-packet"
   EOF

   # Build
   ./ct-ng olddefconfig
   ./ct-ng build.$(nproc)

After this completes, you will find your toolchain in ``~/x-tools``
and can use it to build by setting it as your Zephyr cross compiler:

.. code-block:: shell

   export CROSS_COMPILE=$HOME/x-tools/xtensa-mtk_mt818x_adsp_zephyr-elf/bin/xtensa-mtk_mt818x_adsp_zephyr-elf-
   export ZEPHYR_TOOLCHAIN_VARIANT=cross-compile

Closed-source Tools
===================

Zephyr can also be built by the proprietary Cadence xcc and xt-clang
toolchains.  Support for those tools is beyond the scope of this
document, but it works similarly, by specifying your toolchain and
core identities and paths via the environment, for example:

.. code-block:: shell

   export XTENSA_TOOLS_ROOT=/path/to/XtDevTools
   export XTENSA_CORE=hifi5_7stg_I64D128
   export TOOLCHAIN_VER=RI-2021.6-linux
   export ZEPHYR_TOOLCHAIN_VARIANT=xt-clang
   export XTENSA_TOOLCHAIN_PATH=$XTENSA_TOOLS_ROOT/install/tools
   west build -b mt8186_adsp samples/hello_world