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版本 e0f4ff3a30a5f3895c76711fd7faa59e1a0b83ee

Lab22: RTOS

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

  • 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

  • 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/Lab21-RTOS-shzzlckJ50f>,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>_