Lab1

Please explain what is arm-linux-gnueabihf-gcc? Why don’t we just compile with gcc?
- eabi: 嵌入式ABI，嵌入式應用二進制街口指定了文件格式、數據類型、暫存器使用、堆積組織優化和在一個嵌入式軟件中的參數的標準約定。
- hf: armhf架構，用fpu計算，傳參數也用fpu中的浮點暫存器傳，省去了轉換，性能最好，但是中斷負荷高
- 因為 embedded 和 host 的計算機架構不同，所使用的library也不同，所以不能直接用 gcc
Can executable hello_world run on the host computer? Why or Why not?
- 不行

Lab2

What are the cmake and make for? What is the relationship between them?
- cmake & make 都是編譯工具
- CMake是一种跨平台编译工具，比make更为高级，使用起来要方便得多。CMake主要是编写CMakeLists.txt文件，然后用cmake命令将CMakeLists.txt文件转化为make所需要的makefile文件，最后用make命令编译源码生成可执行程序或共享库（so(shared object)）.它的作用和qt的qmake是相似的。
Why there are so many arguments in the compilation command(step 4.4.2)? What are they for?
- -I：這用於指定編譯器應該查找header files的其他包含目錄
- -L：這用於指定連接器應該查找library的其他庫目錄
- -Wl，-rpath-link：這用於為連接器指定運行時dependent shared library搜索路徑 RUNPATH。這些路徑用於在執行期間查找動態庫（.so文件）
  - provides a hint to the linker about where to find dependent shared libraries during the linking process. It doesn't affect the runtime behavior of the resulting binary or library.
- -lpthread：這鏈接了libpthread庫
- -lopencv_world：這鏈接了OpenCV庫，具體是libopencv_world庫
What is libopencv_world.so.3.4.7 for? Why do we need to use LD_LIBRARY_PATH=. ./demo to run the executable? What would happen if we just run with ./demo ? Why?
- .so: dynamically linked shared object libraries，在執行時動態載入
  - The "world" module in OpenCV is a unified binary/library that contains all the individual OpenCV modules combined. Instead of linking against each module's library separately
- LD_LIBRARY_PATH是Linux環境變數名，該環境變數主要用於指定查找共享庫（動態連結庫）時除了默認路徑之外的其他路徑(/lib & /usr/lib)。
- 程式執行時，當執行函數動態連接.so時，只會從找/lib & /usr/lib，若找不到library則會發生錯誤
It is so complex and difficult to show a picture by using the framebuffer. Why don’t we just use cv::imshow() to do this work?
- cv::imshow(): 在指定視窗中顯示影像(受到螢幕解析度的限制)
- No Windowing System (such as X11 (on Linux))
- Direct Control & Performance
What is a framebuffer?
- framebuffer 是把螢幕上的每個點對映成一段線性記憶體空間，程式可以簡單的改變這段記憶體的值來改變螢幕上某一點的顏色
What is the result of the command below? Why?
- screen redirect to file
- file redirect to frame buffer
- So, 螢幕不會改變

sudo cat /dev/fb0 > fb0 
sudo cat fb0 > /dev/fb0

You can find there is a file named fb1 under /dev directory. What is the difference between /dev/fb0 and /dev/fb1 ? Why we use /dev/fb0 rather than /dev/fb1 ?
- /dev/fb0: primary, 是embedded framebuffer(LCD)
- /dev/fb1: secondary

LABs Details

透過 open + ioctl 來取得 framebuffer 資訊 (/dev/fb0)
藉由 ofstream 寫入到 LCD framebuffer
- DOS: 顯卡 bios 直接對螢幕寫屏
- Linux: 顯卡硬體抽象化，提供 framebuffer 讓用戶直接寫屏
RS-232(UART): 按照1個bit 接著1個bit傳輸 (串列通訊)
- 只用一條線來傳資料，所以它沒有額外的clock
  - 非同步收發傳輸器
- 要設定 baud rate ，盡量跟對方傳輸速度一樣
1. cv::imread 或 cv::VideoCapture 取得圖片資訊
1. BGR to BGR565 (16-bit image) –> LCD requirement
1. ofstream 操作螢幕寫入
- cv::VideoWriter: 錄影
- cv::imwrite: 截圖
- multi-thread: 偵測按鍵輸入

https://zhuanlan.zhihu.com/p/558495267
https://ecomputernotes.com/computer-graphics/basic-of-computer-graphics/what-is-frame-buffer
https://www.cnblogs.com/createyuan/p/4437912.html
https://www.cnblogs.com/liangliangge/p/14403773.html

https://makerpro.cc/2016/07/learning-interfaces-about-uart-i2c-spi/
https://ithelp.ithome.com.tw/articles/10325085?sc=rss.iron
https://www.strongpilab.com/rs232-uart-difference/

Lab1

Lab2

LABs Details

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RTOS

Via SSH to install Teamviewer

Ubuntu install c++ version of OpenCV + opencv_contrib

Install CUDA