---
sub_title: "Real Time Systems 10"
auther: 
  - name: "Finley van Reenen"
    email: "mail@lailatheelf.nl"
    name_short: "E.L.F. van Reenen"
---

# Week 1.3

## assignment 3.1

> Base your code of `opdr_2_1.zip`.  
> Configure the `SysTick` timer to set the `COUNTFLAG` in the `STK_CTRL` register every $0.5s$. Replace the for-loop with the following C code: `while (( STK_CTRL & (1 << 16)) == 0);` You have to properly define the symbol STK_CTRL yourself to make this work. Build and debug the project. If all is well, the user LEDs will blink with a frequency of $1 Hz$.

With bit 2 of `STK_CTRL` the clock source can be set. `1` for `AHB` or `0` for `AHB/8`. `AHB` is by default `HSI` witch is $16MHz$. I chose to use `AHB/8`.

$$
T = \frac{AHB/8}{f_{out}} = \frac{16\cdot 10^6/8}{2} = 10^6
$$

My resulting code^[also available at [/report-2/week_1.3/assignment_3.1/main.c](https://git.gay/LailaTheElf/RTS10_reports/src/branch/main/report-2/week_1.3/assignment_3.1/main.c)]:

```c {.numberLines}
#include <stdint.h>

#define RCC_AHB1ENR_BIT_GPIODEN *(volatile uint32_t*)(0x42000000 + 0x00023830 * 32 + 3 * 4)
#define GPIOD_BASE 0x40020C00
#define GPIOD_MODER *(volatile uint32_t*)(GPIOD_BASE + 0x00)
#define GPIOD_ODR   *(volatile uint32_t*)(GPIOD_BASE + 0x14)

#define STK_CTRL *(volatile uint32_t*)(0xE000E010)
#define STK_LOAD *(volatile uint32_t*)(0xE000E014)

int main(void)
{
    // GPIO Port D Clock Enable
    RCC_AHB1ENR_BIT_GPIODEN = 1;
    // GPIO Port D Pin 15 down to 12 Push/Pull Output
    GPIOD_MODER = 0x55000000;
    // Set green and red LEDs
    GPIOD_ODR = 0x5000;

    // SysTick enable with clk source to AHB/8 
    // (AHB is by default HSI; 16 MHz/8)
    STK_CTRL = 1;
    STK_LOAD = 1000000; // 16 MHz / 8 / 2 Hz
    // Do forever:
    while (1)
    {
        // Wait a moment
        while ((STK_CTRL & (1 << 16)) == 0);
        // Flip all LEDs
        GPIOD_ODR ^= 0xF000;
    }
}
```

I measured the resulting frequency with an logic analyser (figure \ref{31_logic}; channels are coloured to the led colour). It measured a period time of $499.568ms$, I call this error could be my cheap logic analyser or en error in the internal oscillator.

![Logic analiser view of LEDs for assignment 3.1\label{31_logic}](https://live.kladjes.nl/uploads/84591270-95b0-4601-aea2-ca44b51adbf9.png)

## assignment 3.2

> Configure the SysTick timer to set the `COUNTFLAG` in the `STK_CTRL` register every $0.5s$ using the CMSIS API. Replace the for-loop with the following C code: `while ((SysTick->CTRL & (1 << 16)) == 0);` The symbol SysTick is defined in the CMSIS API. Build and debug the project. If all is well, the user LEDs will blink with a frequency of $1 Hz$.

Code also available at [/report-2/week_1.3/assignment_3.2/main.c](https://git.gay/LailaTheElf/RTS10_reports/src/branch/main/report-2/week_1.3/assignment_3.2/main.c)

```c {.numberLines}
#include <stdint.h>
#include <stm32f4xx.h>

int main(void)
{
    // GPIO Port D Clock Enable
    RCC->AHB1ENR = RCC_AHB1ENR_GPIODEN;
    // GPIO Port D Pin 15 down to 12 Push/Pull Output
    GPIOD->MODER = GPIO_MODER_MODER12_0
                   | GPIO_MODER_MODER13_0
                   | GPIO_MODER_MODER14_0
                   | GPIO_MODER_MODER15_0;
    // Set green and red LEDs
    GPIOD->ODR = GPIO_ODR_OD12 | GPIO_ODR_OD14;

    // SysTick enable with clk source to AHB/8
    SysTick->CTRL = SysTick_CTRL_ENABLE_Msk;
    SysTick->LOAD = 1000000; // 16 MHz / 8 / 2 Hz

    // Do forever:
    while (1)
    {
        // Wait a moment
        while ((SysTick->CTRL & (1 << 16)) == 0);
        // Flip all LEDs
        GPIOD->ODR ^= GPIO_ODR_OD12
                      | GPIO_ODR_OD13
                      | GPIO_ODR_OD14
                      | GPIO_ODR_OD15;
    }
}
```

This time I measured $499.586ms$ with the logic analyser.

## assignment 3.3

> B) Configure the SysTick timer to generate an interrupt (also called an exception) every `0.5s`.

code also available at [/report-2/week_1.3/assignment_3.3/main.c](https://git.gay/LailaTheElf/RTS10_reports/src/branch/main/report-2/week_1.3/assignment_3.3/main.c)

```c {.numberLines}
#include <stdint.h>
#include <stdbool.h>

#define RCC_AHB1ENR_BIT_GPIODEN *(volatile uint32_t*)(0x42000000 + 0x00023830 * 32 + 3 * 4)
#define GPIOD_BASE 0x40020C00
#define GPIOD_MODER *(volatile uint32_t*)(GPIOD_BASE + 0x00)
#define GPIOD_ODR   *(volatile uint32_t*)(GPIOD_BASE + 0x14)

#define STK_CTRL *(volatile uint32_t*)(0xE000E010)
#define STK_LOAD *(volatile uint32_t*)(0xE000E014)

volatile bool flag = false;

void SysTick_Handler()
{
    flag = true;
}

int main(void)
{
    // GPIO Port D Clock Enable
    RCC_AHB1ENR_BIT_GPIODEN = 1;
    // GPIO Port D Pin 15 down to 12 Push/Pull Output
    GPIOD_MODER = 0x55000000;
    // Set green and red LEDs
    GPIOD_ODR = 0x5000;

    // SysTick enable with interupt and clk source to AHB/8
	STK_CTRL = (1<<1) | 1;
    STK_LOAD = 1000000; // 0.5 sec / (16 MHz / 8)
    // Do forever:
    while (1)
    {
        // Wait a moment
        while (!flag)
        {
            __asm__("    WFI"); // sleep until SysTick
        }
        flag = false;
        // Flip all LEDs
        GPIOD_ODR ^= 0xF000;
    }
}
```

> C) Why must the flag variable be defined as volatile?

because the compiler doesn't know when `flag` changes. Without `volatile` optimisations can think it does not change at all.

## assignment 3.4

> Configure the SysTick timer to generate an interrupt every `0.5s`. This can be done by using the function `SysTick_Config` from the CMSIS API.

code also available at [/report-2/week_1.3/assignment_3.4/main.c](https://git.gay/LailaTheElf/RTS10_reports/src/branch/main/report-2/week_1.3/assignment_3.4/main.c)

```c {.numberLines}
#include <stdint.h>
#include <stm32f4xx.h>
#include <stdbool.h>

volatile bool flag = false;

void SysTick_Handler()
{
    flag = true;
}

int main(void)
{
    // GPIO Port D Clock Enable
    RCC->AHB1ENR = RCC_AHB1ENR_GPIODEN;
    // GPIO Port D Pin 15 down to 12 Push/Pull Output
    GPIOD->MODER = GPIO_MODER_MODER12_0
                   | GPIO_MODER_MODER13_0
                   | GPIO_MODER_MODER14_0
                   | GPIO_MODER_MODER15_0;
    // Set green and red LEDs
    GPIOD->ODR = GPIO_ODR_OD12 | GPIO_ODR_OD14;

    // SysTick enable with interupt and clk source to AHB/8
    SysTick->CTRL = SysTick_CTRL_TICKINT_Msk | SysTick_CTRL_ENABLE_Msk;
    SysTick->LOAD = 1000000; // 0.5 sec / (16 MHz / 8)

    // Do forever:
    while (1)
    {
        // Wait a moment
        while (!flag)
        {
            __asm__("    WFI"); // sleep until SysTick
        }
        flag = false;
        // Flip all LEDs
        GPIOD->ODR ^= GPIO_ODR_OD12
                      | GPIO_ODR_OD13
                      | GPIO_ODR_OD14
                      | GPIO_ODR_OD15;
    }
}
```

## assignment 3.5

> Now based on project opdr_3_4 create a rotation loop which simulates a simple traffic light: green (5 seconds), orange (1 second), red (4 seconds). The time each light is on must be easily adjustable with a granularity of $0.5s$. The processor must be put to sleep in between interrupts. Make use of an enumeration construct (`enum`) for the colors and a `switch`-`case`-statement for the rotation.

code also available at [/report-2/week_1.3/assignment_3.5/main.c](https://git.gay/LailaTheElf/RTS10_reports/src/branch/main/report-2/week_1.3/assignment_3.5/main.c)

```c {.numberLines}
#include <stdint.h>
#include <stm32f4xx.h>
#include <stdbool.h>

volatile bool flag = false;

void SysTick_Handler()
{
    flag = true;
}

enum STATE {
    STATE_GREEN,
    STATE_ORANGE,
    STATE_RED
};

int main(void)
{
    // GPIO Port D Clock Enable
    RCC->AHB1ENR = RCC_AHB1ENR_GPIODEN;
    // GPIO Port D Pin 15 down to 12 Push/Pull Output
    GPIOD->MODER = GPIO_MODER_MODER12_0
                   | GPIO_MODER_MODER13_0
                   | GPIO_MODER_MODER14_0
                   | GPIO_MODER_MODER15_0;
    // Set green and red LEDs
    GPIOD->ODR = GPIO_ODR_OD12;

    // SysTick enable with interupt and clk source to AHB/8
    SysTick->CTRL = SysTick_CTRL_TICKINT_Msk | SysTick_CTRL_ENABLE_Msk;
    SysTick->LOAD = 1000000; // 0.5 sec / (8 MHz / 8)

    // time of each color in half seconds
    const uint32_t time_green = 10; // 5 seconds
    const uint32_t time_orange = 2; // 1 seconds
    const uint32_t time_red = 8; // 4 seconds

    uint32_t timer = time_green;
    enum STATE State = STATE_GREEN;

    // Do forever:
    while (1)
    {
        // Wait a moment
        while (!flag)
        {
            __asm__("    WFI"); // sleep until SysTick
        }
        flag = false;

        timer--;
        if (timer == 0)
        {
            // turn off all leds
            GPIOD->ODR &= ~(GPIO_ODR_OD12
                            | GPIO_ODR_OD13
                            | GPIO_ODR_OD14
                            | GPIO_ODR_OD15);
            switch (State) {
                case STATE_GREEN:
                    State = STATE_ORANGE;
                    GPIOD->ODR |= GPIO_ODR_OD13;
                    timer = time_orange;
                    break;
                case STATE_ORANGE:
                    State = STATE_RED;
                    GPIOD->ODR |= GPIO_ODR_OD14;
                    timer = time_red;
                    break;
                case STATE_RED:
                    State = STATE_GREEN;
                    GPIOD->ODR |= GPIO_ODR_OD12;
                    timer = time_green;
                    break;
            }
        }
    }
}
```

Again I validated the timings with the logic-analyser.

![](https://live.kladjes.nl/uploads/16fe6424-cff1-4ce4-b506-7f8d87ec4dc4.png)

## assignment 3.6

> - create a copy of the previous project and rename it to opdr_3_6.
> - Using the description of this assignment, define a struct for a “task” and create a global array of 8 empty tasks.
> - Create a function `addTask(...)` to help create a task from a function pointer and other parameters, and add it to the task list (the array) at an appropriate index.
> - Create 4 functions to toggle each led separately, these are the functions that will correspond to 4 tasks.
> - Use `addTask(...)` 4 times to couple each led function to a new task in the task list with periods of: 200 ticks, 500 ticks, 750 ticks, and 300 ticks for green, orange, red, and blue respectively.
> - In the SysTick ISR, walk through the task list and decrement each of the task counters.
> - Think of, and expand on, the task struct to notify per task whether it is in a WAITING or READY state. Set the state in the ISR depending on the task counter.
> - Create a function runReadyTasks() that will walk through the task list and execute any task in the READY state. Replace your switch-case rotation in the function main with a call to this function.
> - Make use of a logic analyzer to verify the timing of the tasks

code also available at [/report-2/week_1.3/assignment_3.6/main.c](https://git.gay/LailaTheElf/RTS10_reports/src/branch/main/report-2/week_1.3/assignment_3.6/main.c)

```c {.numberLines}
#include <stdint.h>
#include <stm32f4xx.h>
#include <stdbool.h>

volatile uint32_t ISR_Ticks = 0;

struct TASK {
    void (*fn)(void);
    uint32_t counter;
    uint32_t counter_rst;
};

uint8_t Tasks_len = 0;
struct TASK Tasks[8];

void SysTick_Handler()
{
    ISR_Ticks++;
}

bool addTask(void  (*fn)(void), uint32_t counter)
{
    if (Tasks_len >= 8) {
        return false;
    }
    Tasks[Tasks_len].fn = fn;
    Tasks[Tasks_len].counter = counter;
    Tasks[Tasks_len].counter_rst = counter;
    Tasks_len++;
    return true;
}

void taskGreen()
{
    GPIOD->ODR ^= GPIO_ODR_OD12;
}

void taskOrange()
{
    GPIOD->ODR ^= GPIO_ODR_OD13;
}

void taskRed()
{
    GPIOD->ODR ^= GPIO_ODR_OD14;
}

void taskBlue()
{
    GPIOD->ODR ^= GPIO_ODR_OD15;
}

enum STATE {
    STATE_GREEN,
    STATE_ORANGE,
    STATE_RED
};

int main(void)
{
    // GPIO Port D Clock Enable
    RCC->AHB1ENR = RCC_AHB1ENR_GPIODEN;
    // GPIO Port D Pin 15 down to 12 Push/Pull Output
    GPIOD->MODER = GPIO_MODER_MODER12_0
                   | GPIO_MODER_MODER13_0
                   | GPIO_MODER_MODER14_0
                   | GPIO_MODER_MODER15_0;
    // Set all leds off
    GPIOD->ODR = 0;


    // SysTick enable with interupt and clk source to AHB/8
    SysTick->CTRL = SysTick_CTRL_TICKINT_Msk | SysTick_CTRL_ENABLE_Msk;
    SysTick->LOAD = 2000; // 1 ms / (16 MHz / 8)

    addTask(*taskGreen, 200);
    addTask(*taskOrange, 500);
    addTask(*taskRed, 750);
    addTask(*taskBlue, 300);

    // Do forever:
    while (1)
    {
        // Wait a moment
        while (ISR_Ticks == 0)
        {
            __asm__("    WFI"); // sleep until SysTick
        }
        uint32_t ticks = ISR_Ticks;
        ISR_Ticks = 0;

        // decrement all counters
        for (uint8_t i=0; i<Tasks_len; i++)
        {
            if (Tasks[i].counter > ticks)
            {
                Tasks[i].counter -= ticks;
            }
            else
            {
                Tasks[i].counter = 0;
            }
        }

        // rust all tasks where the counter has run out
        for (uint8_t i=0; i<Tasks_len; i++)
        {
            if (Tasks[i].counter == 0)
            {
                Tasks[i].fn();
                Tasks[i].counter = Tasks[i].counter_rst;
            }
        }
    }
}
```

![](https://live.kladjes.nl/uploads/c5e6a20b-34ed-4bf0-9bf0-ec175a25e4ae.png)

## Assignment 3.7

> Now add initial delays (in systicks) to your tasks. Use an initial delay of 100, 200, 300, and 400 for green, orange, red, and blue respectively. Make use of a logic analyser to verify the timing.

When A task is created, in the version of [Assignment 3.6], the following function is used: 

```c
bool addTask(void  (*fn)(void), uint32_t counter)
{
    if (Tasks_len >= 8) {
        return false;
    }
    Tasks[Tasks_len].fn = fn;
    Tasks[Tasks_len].counter = counter;
    Tasks[Tasks_len].counter_rst = counter;
    Tasks_len++;
    return true;
}
```

Here the `counter` and `counter_rst` members are set to the same value. `counter` is the counter that is decremented each SysClock. `counter_rst` is the value `counter` is reset to if it reacts 0 after the task is run.

Setting `counter` to the initial delay already solves this assignment. The following code implements this change.

code also available at [/report-2/week_1.3/assignment_3.7/main.c](https://git.gay/LailaTheElf/RTS10_reports/src/branch/main/report-2/week_1.3/assignment_3.7/main.c)

```c {.numberLines}
#include <stdint.h>
#include <stm32f4xx.h>
#include <stdbool.h>

volatile uint32_t ISR_Ticks = 0;

struct TASK {
    void (*fn)(void);
    uint32_t counter;
    uint32_t counter_rst;
};

uint8_t Tasks_len = 0;
struct TASK Tasks[8];

void SysTick_Handler()
{
    ISR_Ticks++;
}

bool addTask(void  (*fn)(void), uint32_t counter, uint32_t counter_init)
{
    if (Tasks_len >= 8) {
        return false;
    }
    Tasks[Tasks_len].fn = fn;
    Tasks[Tasks_len].counter = counter_init;
    Tasks[Tasks_len].counter_rst = counter;
    Tasks_len++;
    return true;
}

void taskGreen()
{
    GPIOD->ODR ^= GPIO_ODR_OD12;
}

void taskOrange()
{
    GPIOD->ODR ^= GPIO_ODR_OD13;
}

void taskRed()
{
    GPIOD->ODR ^= GPIO_ODR_OD14;
}

void taskBlue()
{
    GPIOD->ODR ^= GPIO_ODR_OD15;
}

enum STATE {
    STATE_GREEN,
    STATE_ORANGE,
    STATE_RED
};

int main(void)
{
    // GPIO Port D Clock Enable
    RCC->AHB1ENR = RCC_AHB1ENR_GPIODEN;
    // GPIO Port D Pin 15 down to 12 Push/Pull Output
    GPIOD->MODER = GPIO_MODER_MODER12_0
                   | GPIO_MODER_MODER13_0
                   | GPIO_MODER_MODER14_0
                   | GPIO_MODER_MODER15_0;
    // Set all leds off
    GPIOD->ODR = 0;


    // SysTick enable with interupt and clk source to AHB/8
    SysTick->CTRL = SysTick_CTRL_TICKINT_Msk | SysTick_CTRL_ENABLE_Msk;
    SysTick->LOAD = 2000; // 1 ms / (16 MHz / 8)

    addTask(*taskGreen, 200, 100);
    addTask(*taskOrange, 500, 200);
    addTask(*taskRed, 750, 300);
    addTask(*taskBlue, 300, 400);

    // Do forever:
    while (1)
    {
        // Wait a moment
        while (ISR_Ticks == 0)
        {
            __asm__("    WFI"); // sleep until SysTick
        }
        uint32_t ticks = ISR_Ticks;
        ISR_Ticks = 0;

        // decrement all counters
        for (uint8_t i=0; i<Tasks_len; i++)
        {
            if (Tasks[i].counter > ticks)
            {
                Tasks[i].counter -= ticks;
            }
            else
            {
                Tasks[i].counter = 0;
            }
        }

        // rust all tasks where the counter has run out
        for (uint8_t i=0; i<Tasks_len; i++)
        {
            if (Tasks[i].counter == 0)
            {
                Tasks[i].fn();
                Tasks[i].counter = Tasks[i].counter_rst;
            }
        }
    }
}
```

![](https://live.kladjes.nl/uploads/feb9df6b-ef4d-4bbc-b524-a2ab1d44dc33.png)