---
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)


MMU Configuration in RT-Thread
--------------------------------------------
MRC/MCR Instruction
MMU設定跟Coprocessor 15有關，下圖為Coprocessor 15暫存器配置圖 。

.. image:: https://lh5.googleusercontent.com/-XhcpJ1M19PI/VVC07E249nI/AAAAAAAAIEM/o41r7sl8cwQ/w1083-h564-no/cp15-overview.png
圖四 VMSA: Virtual Memory System Architecture

    MRC: Move to ARM register from coprocessor
    - MRC coproc, opcode1, Rd, CRn, CRm{, opcode2}, where Rd is ARM source register
    MCR: Move to coprocessor from ARM registers
    - MCR coproc, opcode1, Rd, CRn, CRm{, opcode2}, where Rd is ARM source register

MMU Initialization in RT-Thread
       Disable Data Cache
                 mrc p15, 0, r0, c1, c0, 0 /* Read System Control Register */
.. image:: https://lh3.googleusercontent.com/-Rz5eQdg4EcM/VVC5t2eTCjI/AAAAAAAAIEY/9YMC3tQf6yw/w1160-h566-no/cp15-c1.png

VMM (Virtual Machine Module) and vbus
--------------------------------------------
- VMM (Virtual Machine Module)
  VMM模組可同時運行Linux與RT-Thread，如圖五所示。VMM以半虛擬化方式 (para-virtualization)運行另一個OS。

.. image:: https://lh4.googleusercontent.com/-49-7jFwVpZM/VUgwLRtPPqI/AAAAAAAAIBs/w0K4npFRaJg/w939-h634-no/rt-thread-vmm.png
圖五、VMM/vbus Framework

  三個元件需要用來實現同時運行RT-Thread與Linux，如下所述:
    1. Linux VMM Kernel Patches: RT-Thread開發者發佈`兩個Kernel Patches <https://github.com/AdrianHuang/rt-thread-for-vmm/tree/master/components/vmm/linux_patch-v3.8>`_支援多個作業系統同時運行。
    2. Linux VMM Kernel Module (rtvmm.ko): 此模組用來載入RT-Thread Binary File。
    3. RT-Thread Binary File (rtthread.bin): RT-Thread作業系統二進制檔。

[編譯與執行]

`rt-thread-vmm-builder <https://github.com/AdrianHuang/rt-thread-vmm-builder>`_自動地將Linux VMM Kernel Patches、Linux VMM Kernel Module與RT-Thread Binary File編譯，並產生kernel image (zImage)與root file system。參考底下步驟 (同時可參考`rt-thread-vmm-builder README檔 <https://github.com/AdrianHuang/rt-thread-vmm-builder>`_建構環境及相關Toolchain):

.. code-block:: prettyprint

    git clone https://github.com/AdrianHuang/rt-thread-vmm-builder.git
    cd rt-thread-vmm-builder/
    make
    make qemu

執行'make qemu'後， 會啟動qemu模擬器，Linux console與RT-Thread console切換鍵如下:
    1. Linux Console -> Ctrl+Alt+F3
    2. RT-Thread Console -> Ctrl+Alt+F4

[執行畫面]

.. image:: https://lh6.googleusercontent.com/-rhNG5HsX5bk/VX_IJMNczbI/AAAAAAAAIKU/hM1CFIP0cKM/w790-h569-no/linux-1.png
圖六、執行'make qemu'並按Ctrl+Alt+F3進入Linux Console

.. image:: https://lh5.googleusercontent.com/-zM0eIcnkK-U/VX_IJD9ZevI/AAAAAAAAIKM/b_CZuAyN_1o/w1011-h307-no/linux-insmod-rtvmm-driver.png
圖七、載入rtvmm.ko模組

.. image:: https://lh3.googleusercontent.com/-NZlzQBrzD1g/VX_IJOegylI/AAAAAAAAIKQ/cE8BBcgPrPY/w1013-h314-no/rt-thread.png
圖八、Ctrl+Alt+F4進入RT-Thread Console

vbus
    VMM Bus (vbus)用來讓RT-Thread與Linux相互通訊，且可以讓OS之間的功能共享，如圖九所示。

.. image:: https://lh4.googleusercontent.com/-hc_Dy-0dQQ0/VUhFIzyYXPI/AAAAAAAAICE/HxlX6OUO544/w1044-h719-no/vbus-new.png
圖九、VMM Bus

OS之間的功能共享 - Finsh
    圖十把finsh shell指向一個pipe設備，透過該設備把資料寫到ring buffer，並產生一個中斷用以通知另一個OS。另一個OS接收到該中斷後，便從ring buffer中，把資料讀取出來。
.. image:: https://lh6.googleusercontent.com/-sh_c_z-Vqws/VUhHxfi2GuI/AAAAAAAAICc/Sntr8oZV8wI/w1087-h459-no/vbus-finsh-all.png
圖十、Finsh/rsh共享

* Two threads:
  - Thread: "vbusout" (Priority: _BUS_OUT_THRD_PRIO = 8)
  - Thread: "vbusin"   (Priority: _BUS_OUT_THRD_PRIO+1)


* [Source Code]
  - components/vbus/
  - components/drivers/src/pipe.c
  - components/drivers/src/ringbuffer.c


* 支援硬體
  - [LPC4357] Cortex-M0 & Cortex-M4
  - bsp/lpc43xx/M0/applications/vbus_drv.c
  - bsp/lpc43xx/M4/applications/vbus_drv.c


* RTMux
  - 支援硬體
  - [Realview] Cortex-A8
  - [Beagle Board Black] AM33x-based Processor (Cortex-A8)

<Under Construction>

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/>`_