Lab7: RTOS

預期目標

• 學習 OpenOCD 的操作與擴充
• ARM Semihosting 機制的應用

ARM Semihost

• 使用 ARM 所開發的目標系統 (target system)，不一定會提供所有的輸入/輸出設備。因此 ARM 設計了 semihost 這種機制，讓運行 ARM debugger 的主機可以與目標系統進行 I/O 溝通，以利產品開發
  • http://albert-oma.blogspot.tw/2012/04/semihosting.html
• Semihost 的實作是透過使用定義好的軟體中斷 (SVCs)，使程式在執行過程中產生中斷。一旦目標系統上的程式呼叫到對應的指令 (semihosting call)，便產生軟體中斷，接著 Debug Agent 就會負責處理此中斷，進行與主機的溝通
  • http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0205g/Bgbjhiea.html
• sudo apt-get install qemu-user-static
• cd Labs/Lab7
• make factorial
• ./factorial

OpenOCD + STM32F4

• OpenOCD 的安裝請見 Lab-6</embedded/Lab6>_
• ARM On-Chip Debugging demonstration: http://www.youtube.com/watch?v=NSVOuHToJ6c
• Beginner’s look at On-Chip Debugging: http://hackaday.com/2012/09/27/beginners-look-at-on-chip-debugging/
• Architecture and Core Commands of OpenOCD
  • http://openocd.sourceforge.net/doc/html/Architecture-and-Core-Commands.html
  • Command: arm semihosting [enable|disable]
    • Display status of semihosting, after optionally changing that status.
    • “Semihosting allows for code executing on an ARM target to use the I/O facilities on the host computer i.e. the system where OpenOCD is running. The target application must be linked against a library implementing the ARM semihosting convention that forwards operation requests by using a special SVC instruction that is trapped at the Supervisor Call vector by OpenOCD.”