doc: develop: toolchains: add description for Andes toolchain

Add documentation for the Andes toolchain support both GCC and Clang.

Signed-off-by: Jimmy Zheng <jimmyzhe@andestech.com>

Author: jimmyzhe

doc/develop/toolchains/andes_toolchain.rst

@@ -0,0 +1,41 @@
+.. _toolchain_andes:
+
+Andes Toolchain
+##############
+
+#. Download and extract a toolchain from `Andes-Development-Kit`_ for your
+   operating system.
+
+   .. note::
+   The currently supported release is **ast-v5_3_3-release** and later for Linux
+   and MinGW-based Windows toolchain. Cygwin-based Windows toolchains
+   (e.g. *ast-v5_3_3-release-windows*) are **not** supported.
+
+#. :ref:`Set these environment variables <env_vars>`:
+
+   - Set :envvar:`ZEPHYR_TOOLCHAIN_VARIANT` to ``andes`` or ``andes-clang``.
+   - Set :envvar:`ANDES_TOOLCHAIN_PATH` to the toolchain installation directory.
+
+#. For example
+
+   #. Andes GCC:
+
+      .. code-block:: console
+         # Linux
+         export ZEPHYR_TOOLCHAIN_VARIANT=andes
+         export ANDES_TOOLCHAIN_PATH=/path/to/nds32le-elf-mculib-v5
+
+   #. Andes Clang:
+
+      .. code-block:: console
+         # Linux
+         export ZEPHYR_TOOLCHAIN_VARIANT=andes-clang
+         export ANDES_TOOLCHAIN_PATH=/path/to/nds32le-elf-mculib-v5
+
+      Andes Clang toolchain uses LLVM linker by default. You can choose the
+      linker via Kconfig:
+
+      - Set :envvar:`CONFIG_LLVM_USE_LLD=y` to use LLVM linker.
+      - set :envvar:`CONFIG_LLVM_USE_LD=y` to use the GNU LD linker.
+
+.. _Andes-Development-Kit: https://github.com/andestech/Andes-Development-Kit/releases

doc/develop/toolchains/index.rst

@@ -10,6 +10,7 @@ Guides on how to set up toolchains for Zephyr development.
 
    zephyr_sdk.rst
 
+   andes_toolchain.rst
    arm_compiler_6.rst
    arm_toolchain_for_embedded.rst
    cadence_xcc.rst