KW41Z-Dev

The idea of this lab exercise is to get experience and realise the pros and cons of different development environments. To demonstrate this, a simple RTOS program will be written, flashed and debugged for the FRDM-KW41Z on three different development environments:

1. ARM Keil
2. NXP MCUXpresso
3. GNU FOSS Toolchain and Makefiles

The directory structure for this repository is as follows:

KW41Z-Dev/
├── GNU/
│   ├── README.md
│   ├── RTOS_Blink/
│   └── img/
├── Keil/
│   ├── README.md
│   ├── RTOS\ Blink/
│   └── img/
├── MCUXpresso/
│   ├── README.md
│   ├── RTOS_Blink/
│   └── img/
└── README.md

---

Simple RTOS Program

The RTOS program that will be written for the processor will simply toggle two different LEDs with different periods. A red on at 500ms, and a green one at 330ms.

Below is segments of the FreeRTOS functionality ONLY, i.e. no development platform specific functions or includes.

Main Function

The job of the main function is to create the two LED tasks and begin the OS scheduler.

int main(void)
{
    // Create red LED task.
    xTaskCreate(
        LEDTask1, // Task function.
        "LEDTask1", // Task name (for simulations).
        configMINIMAL_STACK_SIZE, // Size of task stack.
        (void *)NULL, // Parameter passed to task at startup.
        (unsigned portBASE_TYPE)tskIDLE_PRIORITY+1, // Priority.
        (xTaskHandle *)NULL // Pointer to reference of the task.
    );

    // Create green LED task.
    xTaskCreate(
        LEDTask2, // Task function.
        "LEDTask2", // Task name (for simulations).
        configMINIMAL_STACK_SIZE, // Size of task stack.
        (void *)NULL, // Parameter passed to task at startup.
        (unsigned portBASE_TYPE)tskIDLE_PRIORITY+1, // Priority.
        (xTaskHandle *)NULL // Pointer to reference of the task.
    );

    // Start OS scheduler.
    vTaskStartScheduler(); // No return!

    return 0;
}

LED Tasks

The LED tasks are very basic. They consist of a while loop that forever turns on an LED, waits a period of time, then turns off the LED before again waiting. This is not at all efficient code however it is meant to only be a simple example.

void LEDTaskN(void *pvPs)
{
    while (42) {
        // Turn LED on.
        vTaskDelay( tDelay_ms(500) );
        // Turn LED off.
        vTaskDelay( tDelay_ms(500) );
    }
}

Converting RTOS Ticks to Seconds

For the vTaskDelay function, we cannot simply pass a millisecond wait time, we need to convert this to RTOS processor ticks which is done using a small converter function.

portTickType tDelay_ms(const float ms)
{
    return (portTickType)(ms / portTICK_PERIOD_MS);
}

---

Comparison Between Development Platforms

ARM Keil

Pros

• Easy to use debugging interface.
• Able to batch build for multiple targets.
• Well designed and easy to use package manager.

Cons

• 32kB code limit.
• Very expensive full version of the software.
• Pulls in files from a variety of locations. Not sure what you're including.

MCUXpresso

Pros

• Cross-platform IDE.
• Free.
• IDEs allow more time writing code rather than wasting time figuring out the toolchains.
• Easy debugging interface.
• Familiarity to those who have used Eclipse tools in the past.

Cons

• Based on Eclipse so is a fairly heavy editor for embedded platforms.
  • Most of Eclipse isn't even used!

GNU Toolchains

Pros

• Free.
• You know exactly what files are being compiled into your project.
  • More control over code size.
  • More control over security.
    • Not pulling in random libraries you didn't write.
• Lightweight IDEs.
  • Just need a text editor and a terminal.
  • Use whatever text editor you like.
    • Atom
    • Vi/Vim
    • Nano
    • Notepad++

Cons

• Makefiles can be very complicated/convoluted.
  • Spend more time debugging makefiles rather than actual code.
• More complicated methods of making linker scripts.
• More time spent setting up the toolchains rather than actually writing functional code for the target.
• GDB in the command line has a steep learning curve.