---
title: Week #3 (Mar 10) :: ARM Architecture
toc: no
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教材
----------
* fork()  系統呼叫的原理
  - `一個fork的面試題<http://coolshell.cn/articles/7965.html>`_
    + 假設 fork.c 編譯出來的結果是 ``fork``，則可用這個指令計算 '-' 數量: ``./fork | wc -c``

  - `In fork() which will run first, parent or child?<http://stackoverflow.com/questions/21586292/in-fork-which-will-run-first-parent-or-child>`_
    + ``sudo sysctl -w kernel.sched_child_runs_first=1``
    + `基本能力鑑定</embedded/2015q1w2>`_ 的第 4 題題意不清，所以沒有辦法作答

* `Introduction to ARM Architecture<https://docs.google.com/presentation/d/1cFBRICktpVQAOLzE5eDKD-OM4ckJuncFsn39Wg8aLZI/edit#slide=id.p14>`_
  - `ARM Conditional Execution<http://www.davespace.co.uk/arm/introduction-to-arm/conditional.html>`_，以 C 程式來說:

.. code-block:: prettyprint

    if (z == 1) R1 = R2 + (R3 * 4) 

對應的 ARM 組合語言為

.. code-block:: prettyprint

    addeqs r1, r2, r3, lsl #2