--- title: RT-Thread categories: embedded, arm, rtos, rt-thread, beaglebone, am335x toc: no ... 協作者 --- * 2015 年春季 - `周曠宇`_, `吳子晨`_, `Adrian Huang`_, `吳念祖`_, `吳義路`_, `江冠霆`_ 共筆 ---- * 2015 年春季 - `Hackpad`_ 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`_與`freertos`_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 `_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 `_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 `_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 參考資料 -------------------------------------------- * Beaglebone - `Rev. changes`_ - `Schematic`_ - `System Reference Manual`_ * AM335x (3358) TRM, Datasheet - `TRM`_ - `Datasheet`_ - `Boot process`_ * ARM Cortex-A8 - `TRM`_ - ISA: `①`_ `②`_ - Bus: - `AMBA`_ - `APB`_ - `AXI`_ * POSIX - `The Open Group Base Specifications Issue 7`_ - `Open POSIX Test Suite`_ * EMMC - `Kingston KE4CN2H5A`_