feat: add zephyr implementation

cmake/Generic.cmake

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+#********************************************************************
+#        _       _         _
+#  _ __ | |_  _ | |  __ _ | |__   ___
+# | '__|| __|(_)| | / _` || '_ \ / __|
+# | |   | |_  _ | || (_| || |_) |\__ \
+# |_|    \__|(_)|_| \__,_||_.__/ |___/
+#
+# www.rt-labs.com
+# Copyright 2026 rt-labs AB, Sweden.
+#
+# This software is licensed under the terms of the BSD 3-clause
+# license. See the file LICENSE distributed with this software for
+# full license information.
+#*******************************************************************/
+
+if(ZEPHYR_BASE)
+    include(${CMAKE_CURRENT_LIST_DIR}/Zephyr.cmake)
+endif()

cmake/Zephyr.cmake

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+#********************************************************************
+#        _       _         _
+#  _ __ | |_  _ | |  __ _ | |__   ___
+# | '__|| __|(_)| | / _` || '_ \ / __|
+# | |   | |_  _ | || (_| || |_) |\__ \
+# |_|    \__|(_)|_| \__,_||_.__/ |___/
+#
+# www.rt-labs.com
+# Copyright 2026 rt-labs AB, Sweden.
+#
+# This software is licensed under the terms of the BSD 3-clause
+# license. See the file LICENSE distributed with this software for
+# full license information.
+#*******************************************************************/
+
+add_subdirectory(src/zephyr)
+
+set (OSAL_DEFAULT_SYSTEM
+  osal-zephyr
+  CACHE STRING ${OSAL_DEFAULT_SYSTEM_HELP_STRING})

src/zephyr/CMakeLists.txt

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+#********************************************************************
+#        _       _         _
+#  _ __ | |_  _ | |  __ _ | |__   ___
+# | '__|| __|(_)| | / _` || '_ \ / __|
+# | |   | |_  _ | || (_| || |_) |\__ \
+# |_|    \__|(_)|_| \__,_||_.__/ |___/
+#
+# www.rt-labs.com
+# Copyright 2017 rt-labs AB, Sweden.
+#
+# This software is licensed under the terms of the BSD 3-clause
+# license. See the file LICENSE distributed with this software for
+# full license information.
+#*******************************************************************/
+
+set(_osal_sys osal-zephyr)
+add_library(${_osal_sys})
+
+add_dependencies(${_osal_sys} zephyr_generated_headers)
+
+target_compile_features(${_osal_sys}
+  PUBLIC
+  c_std_99
+  )
+
+target_sources(${_osal_sys}
+  PRIVATE
+  osal.c
+  osal_log.c
+  )
+
+target_compile_options(${_osal_sys}
+  PRIVATE
+  -Wall
+  -Wextra
+  -Werror
+  -Wno-unused-parameter
+  )
+
+target_link_libraries(${_osal_sys}
+  PUBLIC
+  osal-interface
+  PRIVATE
+  $<BUILD_INTERFACE:zephyr_interface>
+  $<BUILD_INTERFACE:kernel>
+  )
+
+target_include_directories(${_osal_sys}
+  PRIVATE
+  sys
+  )
+
+install(
+  TARGETS ${_osal_sys}
+  EXPORT OsalTargets
+  )

src/zephyr/README.md

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+# OSAL Zephyr backend
+
+## Required Kconfig options
+
+Applications linking against `osal` on Zephyr need the following in
+their `prj.conf`:
+
+```
+CONFIG_HEAP_MEM_POOL_SIZE=<size>
+CONFIG_THREAD_STACK_INFO=y
+CONFIG_DYNAMIC_THREAD=y
+CONFIG_DYNAMIC_THREAD_ALLOC=y
+CONFIG_EVENTS=y
+CONFIG_THREAD_NAME=y
+CONFIG_LOG=y
+```
+
+- `HEAP_MEM_POOL_SIZE`: backs `k_malloc`/`k_free`, used throughout `osal.c`.
+- `THREAD_STACK_INFO`: required by `DYNAMIC_THREAD`.
+- `DYNAMIC_THREAD` + `DYNAMIC_THREAD_ALLOC`: `os_thread_create()` takes a
+  runtime stack size, so stacks are heap-allocated via
+  `k_thread_stack_alloc()` rather than declared statically.
+- `EVENTS`: backs `os_event_*()` (`k_event`).
+- `THREAD_NAME`: `os_thread_create()` sets the Zephyr thread name from
+  its `name` argument.
+- `LOG`: backs `os_log()` (`osal_log.c`). Without it, log calls compile
+  down to no-ops.
+
+## Linking
+
+Link against `osal` normally:
+
+```cmake
+target_link_libraries(app PRIVATE osal)
+```