sample: mbox: Introduce MBOX NRFX IPC sample

Make use of the new MBOX APIs to create a ping-pong sample application.
This sample is using the NRFX IPC peripheral to send and receive signals
on different channels

Signed-off-by: Carlo Caione <ccaione@baylibre.com>

samples/drivers/mbox/CMakeLists.txt

@@ -0,0 +1,36 @@
+#
+# Copyright (c) 2021 Carlo Caione <ccaione@baylibre.com>
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+cmake_minimum_required(VERSION 3.20.0)
+
+set(REMOTE_ZEPHYR_DIR ${CMAKE_CURRENT_BINARY_DIR}/mbox_ipc_remote-prefix/src/mbox_ipc_remote-build/zephyr)
+
+if("${BOARD}" STREQUAL "nrf5340dk_nrf5340_cpuapp")
+  set(BOARD_REMOTE "nrf5340dk_nrf5340_cpunet")
+else()
+  message(FATAL_ERROR "${BOARD} is not supported for this sample")
+endif()
+
+message(INFO " ${BOARD} compile as Main in this sample")
+
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(mbox_ipc)
+
+enable_language(C ASM)
+
+target_sources(app PRIVATE src/main.c)
+
+include(ExternalProject)
+
+ExternalProject_Add(
+  mbox_ipc_remote
+  SOURCE_DIR ${APPLICATION_SOURCE_DIR}/remote
+  INSTALL_COMMAND ""      # This particular build system has no install command
+  CMAKE_CACHE_ARGS -DBOARD:STRING=${BOARD_REMOTE}
+  BUILD_BYPRODUCTS "${REMOTE_ZEPHYR_DIR}/${KERNEL_BIN_NAME}"
+  # NB: Do we need to pass on more CMake variables?
+  BUILD_ALWAYS True
+)