---
title: Lab22: RTOS
toc: no
...

預期目標
-------
* 在 QEMU 模擬的 STM32 環境中，嘗試執行 `FreeRTOS<http://www.freertos.org/>`_ 並且學習相關的操作
  - 熟悉 FreeRTOS 的內部運作機制

* 學習 memory mangement
  - 實作 ``malloc`` / ``free`` 和驗證其功能
  - 搭配 `Week #5</embedded/2013-w5>`_ 進度，學習 heap, stack 的規劃
  - defragmentation

FreeRTOS
---------------
* `The Architecture of Open Source Applications: FreeRTOS<http://www.aosabook.org/en/freertos.html>`_
  - `簡體中文翻譯<http://www.ituring.com.cn/article/4063>`_

FreeRTOS: Memory management
-------------------------------
- `Memory Management<http://www.freertos.org/a00111.html>`_
-  The RTOS kernel allocates RAM each time a task, queue, mutex, software timer or semaphore is created. The standard C library malloc() and free() functions can sometimes be used for this purpose, but ...
    + they are not always available on embedded systems,
    + they take up valuable code space,
    + they are not thread safe, and
    + they are not deterministic (the amount of time taken to execute the function will differ from call to call)

- 檢查 freertos 目錄的 Makefile，目前使用 ``$(FREERTOS_SRC)/portable/MemMang/heap_1.c``，可更換為 ``heap_2.c``

hack-malloc
-------------------
* 簡易 malloc/free 測試程式，以亂數指定若干不同大小的 memory region，持續進行 malloc 和 free 操作
* ``git clone git@github.com:embedded2013/hack-malloc.git`` # 或 ``git clone git://github.com:embedded2013/hack-malloc.git`
* ``cd hack-malloc && make``
* ``./tryit`` # Ctrl-C 停止輸出
* 參考畫面輸出：

.. code-block:: prettyprint

    tryit.c 68: try to allocate 1648 bytes
    tryit.c 70: malloc returned 0x61595c
    allocate a block, size 1648
    tryit.c 68: try to allocate 1582 bytes
    tryit.c 70: malloc returned 0x615fe8
    allocate a block, size 1582
    tryit.c 68: try to allocate 1037 bytes
    tryit.c 70: malloc returned (nil)
    free a block, size 1648
    tryit.c 68: try to allocate 1815 bytes
    tryit.c 70: malloc returned (nil)
    free a block, size 1582

參考作業提案
--------------------
* 將 ``tryit`` 移植回去 FreeRTOS，並且配合 Lab 21，在 shell 中建立一個命令: ``mmtest``
  - 加分: 將 ``tryit`` 移植回去 ``rtenv``

* 修改 ``tryit.c`` 的 prng (pseudorandom number generator)，用 inline assembly 重寫該函式
* 提出檢驗 FreeRTOS/rtenv 中 ``malloc`` / ``free`` 功能的方法 (需要提案描述)
  - 加分: defragmentation 的途徑


作業繳交方式
-------------------
* 更新作業提案到共筆網站: `Lab 22 / 作業共筆<https://embedded2013.hackpad.com/Lab22-RTOS-wnRrVcPhtUU>`_，需要標注自己的 ID，可參考 `Lab 20 / 作業共筆<https://embedded2013.hackpad.com/Lab20-GNU-Toolchain-zI6gzN3uv1c>`_ 格式
* 在 Oct 25, 2013 前，將符合作業提案的程式碼，提交到自行 fork 的 repository
   - https://github.com/embedded2013/freertos

參考資訊
-------------
* `FreeRTOS Implementation<http://www.freertos.org/implementation/main.html>`_
* `ARM GCC Inline Assembler Cookbook<http://www.ethernut.de/en/documents/arm-inline-asm.html>`_