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chapter02_02

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Example chapter02_02

The LED program

This example implements the LED program (blinky) for the target with the 8-bit microcontroller. This example has originally been presented in the book with a homemade microcontroller board. The project also runs and blinks the LED on an Arduino board or an Arduino-compatible board.

Building the example can be done with command batch or shell script. There is also CMake support.

The build executes several straightforward actions in a very clear sequence of steps. In fact, to study this build is a great way to gain introductory skills in manually calling embedded tools and making more complicated builds on your own in the future.

The results of the build will be stored in the bin directory. After successful build, files such as the HEX-file led.hex and othe name and map files can be found in bin.

The steps of the build include the following.

  • Assemble : crt0.s to bin/crt0.o
  • Compile : led.cpp to bin/led.o
  • Link : objects to bin/led.elf
  • Extract : executalbe hex file : from bin/led.elf
  • Extract : assembly list file : from bin/led.elf
  • Extract : size information : from bin/led.elf
  • Extract : name information : from bin/led.elf
  • Extract : demangled names : from bin/led.elf

Blinking Frequency

In the LED program, the blinking is controlled directly from the main subroutine of the program. The blinking frequency will be as fast as the microcontroller can execute the given toggle code, which will be too fast to resolve.

Use the commented out loop in the program to slow down the blinking for easier observation. The commented out loop is reproduced below within its contect in main. It is the line starting with for(volatile std::uint8_t delay...).

int main()
{
  // Toggle led_b5 in a loop forever.
  for(;;)
  {
    led_b5.toggle();

    // Some boards have a slower LED electrical
    // response on the port. Optionally activate
    // delay loop if LED toggle is not visible.
    //for(volatile std::uint8_t delay = UINT8_C(0); delay < UINT8_C(10); ++delay) { ; }
  }
}

In Win*

The Win* batch file searches for a pre-installed instance of the avr-g++ tool chain.

When in Win*, building the Example chapter02_02 project can accomplished in a cmd window. Use a command command such as shown below, where the full path of the pre-installed gcc-avr is listed in its entirety.

build.bat "C:\Program Files (x86)\gcc-7.2.0-avr\bin" avr

In *nix

On *nix-like systems, gcc-avr can be installed from a package manager. A common example is shown below.

apt-get install gcc-avr avr-libc

Building the Example chapter02_02 project can be done with a bash shell such as:

## bash will typically use dirname, so this might be equivalent to: ./build.sh /usr/bin avr
./build.sh "$(dirname $(which avr-g++))" avr