Embedded Software Tutorials

Video Episode 2

Take-out from section 2

  • Emphasis the concept of a bus. Think of the bus as a connection between the CPU and peripherals (like I2C, SPI, etc.) and high speed modules like GPU, high speed RAM etc.

  • The role of a bus is to make the CPU easy to be connected to extensive modules. Also, the bus coordinates the frequency of each module.

Take-out from section 4

  • This section focuses on bus and addressing in a very brief way.

  • There is a trick though to check the I/O memory on a Embedded Linux. Enter /proc, and $ cat iomem.

  • x86 has commands to direct control I/O devices. There is a dedicated 64K memory for those devices, and one could use $ cat ioports. In ARM SoCs, $ cat ioports may return nothing as no dedicated memory is allowed.

Take-out from section 5

  • ISA: instruction set architecture. Defines machine language mnemonic i.e., assembly. Micro-architecture: implementation of the ISA, like arythmic or control operations.

  • A very brief history of ARM architecture. ARM Cortex-M, Cortex-A and Cortex-R were launched as part of ARM v7 architecture, while Cortex-M50, Cortex-M53 and Cortex-M57 were part of ARM v8 architecture.

Video Episode 8

  1. Session 23 and 24 were skimmed through. The contents are mostly concepts.

  2. Take-out from section 2: $ gcc -c xxx.c will eventually generate an object file. If $ readelf -S xxx.o, one should be able to read multiple sections like .text, .rodata, .data, .bss, elf header etc.

    • When use gcc to link object files, the final executable would merge each section of object files.

    • To conduct symbol table parsing, use $ readelf -s xxx.

  3. Section 3 is useless.

  4. Section 4 is useless.

  5. Section 5 is useless.

  6. Section 6 contains a walk-through of the header files in Linux source. Also a way to utilize makefile to include header paths (-I/path/). Some tricks are worth noting:

    • $ man 3 function to check which glibc header file defines which function, .e.g., $ man 3 malloc.

    • $ grep -rin function to get recursively (r) file lines (with line number -n) containing function name with ignored-case (-i).

  7. There is an interesting point in section 7. In Linux headers, one could always be seeing static inline xxx(), i.e., static inline functions. The reason why to add a static is because:

    • Firstly, inline functions could be treated as either a normal function or a content extensive function regardless of argument pass in return value etc.

    • Secondly, if the inline function is treated as a normal function by the compiler, it’d incur redefinition if multiple files includes such a header. Adding static makes it being locally seen to the c file.

The rest of this episode looks useless.