---
title: RT-Thread
categories: embedded, arm, rtos, rt-thread, beaglebone, am335x
toc: no
...

協作者
---
* 2015 年春季
   - `周曠宇<https://github.com/luckyjoou>`_, `吳子晨<https://github.com/Eddy0402>`_, `Adrian Huang<https://github.com/AdrianHuang>`_, `吳念祖<https://github.com/nienzu>`_, `吳義路<https://github.com/jackraken>`_, `江冠霆<https://github.com/CKT-tw>`_

共筆
----
* 2015 年春季
   - `Hackpad<https://rt-thread.hackpad.com/RT-Thread-on-Beaglebone-Black-i93C7gRxZuW>`_

目錄
---
* `AM335x ARM Cortex-A8 Boot Sequence<#AM335x ARM Cortex-A8 Boot Sequence>`_

AM335x ARM Cortex-A8 Boot Sequence
--------------------------------------------
圖1 為AM335x開機流程，其包含ROM Code、MLO、U-Boot與OS Image，底下將說明ROM Code、MLO與U-Boot。

.. image:: https://lh3.googleusercontent.com/-6t7H14Lj3Bc/VT3n0BPjOaI/AAAAAAAAH9M/woI49MW-TC4/w1099-h752-no/am335x-boot-sequence.png
圖1 High-level Overview to AM335x Boot Sequence

ROM Code主要有幾項任務:
  - Stack Setup
  - Watchdog timer 1  configuration (set to three minutes)
  - System clock configuration
  - Search bootable devices (must be the FAT 12/16/32 partition) for a valid booting image (the image name must be MLO)
  - Load the content of the file "MLO" from a bootable device to internal RAM (the 128KB on-chip memory)
  - Execute the file "MLO" stored in internal RAM

圖2為ROM Code架構，由"Public ROM Code drivers"可知ROM code支援如下裝置:
  - MMCSD (MultiMediaCard SD)
  - NAND
  - XIP (eXecute In Place)
  - SPI
  - USB UART
  - EMAC (Ethernet Media Access Control)

也就是說，系統一上電，ROM Code會掃描上述裝置，以便找到Bootable device。由於ROM Code只支援FAT檔案系統格式，所以Bootable device一定要是FAT檔案系統 (FAT12/16/32檔案系統都可以)。
注意: 該架構的On-chip boot ROM大小為176 KB。

.. image:: https://lh5.googleusercontent.com/-ClS3EZ2u0Hk/VT33Y8THfxI/AAAAAAAAH9w/t9gFp9N6ajM/w1011-h631-no/ROM-code-architecture.png
圖2 ROM Code Architecuture (page 4096 in AM335x TRM)

圖3為ROM Memory Map:
  - ROM Exception Vectors (0x20000-0x2001F): 該區段定義Exception Handler的位址。譬如: 0x20000存放Reset Handler的位址，也就是板子一上電，第一個執行的地方，課程第七周有詳盡的說明，可參考此文件。詳盡的ROM Exception Vectors如表1所示。

.. image:: https://lh5.googleusercontent.com/-ClS3EZ2u0Hk/VT33Y8THfxI/AAAAAAAAH9w/t9gFp9N6ajM/w1011-h631-no/ROM-code-architecture.png
表1 ROM Exception Vectors (page 4099 in AM335x TRM)

  - Public ROM Code CRC (0x20020): 由0x20000-0x2BFFF計算得出的四個位元組CRC值。
  - Dead loops (0x20080-0x200FF): 該區段定義預設的exception handlers，其預設handlers都是執行while(1)迴圈，程式設計者可以定義相同名字的exception handler，如此便能覆蓋 (override)對應之預設exception handlers。可參考`mini-arm-os<https://github.com/jserv/mini-arm-os/blob/master/05-TimerInterrupt/startup.c#L63>`_與`freertos<https://github.com/embedded2015/freertos-basic/blob/master/freertos/libraries/CMSIS/CM3/DeviceSupport/ST/STM32F10x/startup/gcc_ride7/startup_stm32f10x_md.s#L124>`_程式碼，以便了解其設計概念。
  - Code (started from 0x20100): ROM程式碼
  - ROM Version (0x2BFFC-0x2BFFF): ROM Code Version

.. image:: https://lh3.googleusercontent.com/-xhXu1yv0eik/VT33Y0MPSDI/AAAAAAAAH9k/S7dXDW7UrGI/w306-h329-no/ROM-memory-map.png
圖3 ROM Memory Map (page 4098 in AM335x TRM)


參考資料
--------------------------------------------
* Beaglebone
  - `Rev. changes<http://elinux.org/Beagleboard:BeagleBoneBlack#Revision_C_.28Production_Version.29>`_
  - `Schematic<http://beagleboard.org/static/beaglebone/latest/Docs/Hardware/BONE_SCH.pdf>`_
  - `System Reference Manual<http://docs-asia.electrocomponents.com/webdocs/12d7/0900766b812d788b.pdf>`_

* AM335x (3358) TRM, Datasheet
  - `TRM<https://drive.google.com/open?id=0B90H2V1uw2FnVmNndG5jV3V5N2M&authuser=0>`_
  - `Datasheet<https://drive.google.com/open?id=0B90H2V1uw2FnbzFDZTNpRC1jOGc&authuser=0>`_
  - `Boot process<http://processors.wiki.ti.com/index.php/AM335x_U-Boot_User%27s_Guide#U-Boot>`_

* ARM Cortex-A8
  - `TRM<https://drive.google.com/open?id=0B90H2V1uw2FnRnJOSlpzTm4yWFU&authuser=0>`_
  - ISA: `①<https://drive.google.com/open?id=0B90H2V1uw2FnUEZzWFpmR3JKa1U&authuser=0>`_ `②<http://people.cs.nctu.edu.tw/~chenwj/dokuwiki/doku.php?id=arm>`_
  - Bus:
    - `AMBA<https://drive.google.com/open?id=0B90H2V1uw2FnRHpIWGJLaUUwZzA&authuser=0>`_
    - `APB<https://drive.google.com/open?id=0B90H2V1uw2FnUEZzWFpmR3JKa1U&authuser=0>`_
    - `AXI<https://drive.google.com/open?id=0B90H2V1uw2FnSVBERUdFUFlsZkE&authuser=0>`_

* POSIX
  - `The Open Group Base Specifications Issue 7<http://pubs.opengroup.org/onlinepubs/9699919799//>`_
  - `Open POSIX Test Suite<http://posixtest.sourceforge.net/>`_

* EMMC
  - `Kingston KE4CN2H5A<http://uk.rs-online.com/web/p/flash-memory-chips/7852322P/>`_