How to create an interrupt or background task in C - c

Question

I am trying to figure out how to make a background process in C, I haven't found anything online. I think the reason I haven't found much is that I may not be asking the right question.
I am working on a school project using ARM assembly and C with Raspberry Pi using the Raspbian Operating System and the GCC compiler.
For my project, I decided to do a simple alarm system. The idea is simple, I have 3 PIR sensors that detect motion, and set off a buzzer when motion is detected.
Instead of using hardware for the keypad, I chose to do a GUI where you can arm/disarm the system as well as change the password and turn on/off certain sensors. For example, if you wanted to turn off motion sensors 1 and 2, there will be buttons on the GUI to do that.
The problem I am having is that the GUI Library I'm using, (GTK3 and Glade) is event-driven, so unless a button is pressed it won't do anything. This would be fine if I only wanted to set the buzzer to on when motion is detected because I could make my own loop to watch for motion, but I really want to play some type of pattern repeatedly (example: 3 short beeps continuously until the alarm is disarmed). At the same time, I still want to have access to the GUI buttons so I can turn off the alarm. This makes me think I need an interrupt or a background process.
I'm sure there are many ways to solve this problem, but I really wanted to create sort of a background routine that could run parallel to the main task once the user's arms' the system. I have asked my professor about how to multi-thread in ARM, but he said that we do not cover this in the class. I have read that the C standard library doesn't support multi-threading, but I am sure there is a way that this can be done. If someone could just point me in the right direction I would be grateful.
Here is the GUI code I have written, along with another module I have finished to get a working prototype before I start wiring the sensors. None of this contains any assembly code because I haven't got to that yet, I wanted to get it working at a higher level and then break certain parts down to assembly. If you need all of the files I will gladly provide them, but I think this should be enough for you all to understand what I'm trying to do.
The GUI code:
/*****************************************************
* Title: User Interface
* Author:
* Date: 2/15/20
* Class: CISP 2410
*
* Description:
* ! This header file contains all of the function
* ! Declarations and definitions for the GUI
* ! Everything involving the GUI will be in
* --> this header
*
*****************************************************/
#include <gtk/gtk.h> // For gtk stuff
#include <stdlib.h> // Standard Library
#include "GUI_Ctrl.h" // Prototypes
#include "Alarm.h" // Alarm Functions
/* Private Functions */
static void UpdateLcdDisplay(char keyPadValue);
static void ClearLcdDisplay(void);
static void UpdateDisplay(void);
/***********************************/
// Global Variables
GtkWidget *g_Lbl_Lcd;
GtkWidget *g_Lbl_SysStat;
GtkWidget *g_Lbl_LogStat;
char inputBuffer[6] = {0x0};
int charCounter = 0;
const int INPUT_LIMIT = 6;
/*****************************************************
* ! Initializes all of the GUI elements
* ! Adds CSS attributes to GUI elements
* ! Also handles the formatting of text
*****************************************************/
void GUI_INIT(int argc, char* argv[])
{
GtkBuilder *builder;
GtkWidget *window;
GtkWidget *g_Lbl_Lbl1;
GtkWidget *g_Lbl_Lbl2;
// Get pointer to css file
GtkCssProvider *cssProvider = gtk_css_provider_new ();
gtk_css_provider_load_from_path(cssProvider,"UI/style.css",NULL);
gtk_init(&argc, &argv);
// get pointer to xml dat file
builder = gtk_builder_new_from_file("UI/HelloWorld.glade");
// Get pointer to main window
window = GTK_WIDGET(gtk_builder_get_object(builder, "window_main"));
gtk_builder_connect_signals(builder, NULL);
// Get pointer to labels
g_Lbl_Lcd = GTK_WIDGET(gtk_builder_get_object(builder, "Lbl_Lcd"));
g_Lbl_SysStat = GTK_WIDGET(gtk_builder_get_object(builder, "Lbl_SysStat"));
g_Lbl_LogStat = GTK_WIDGET(gtk_builder_get_object(builder, "Lbl_LogStat"));
g_Lbl_Lbl1 = GTK_WIDGET(gtk_builder_get_object(builder, "Lbl1"));
g_Lbl_Lbl2 = GTK_WIDGET(gtk_builder_get_object(builder, "Lbl2"));
// Align Text Right
gtk_label_set_xalign (GTK_LABEL(g_Lbl_Lcd), 1);
// Align Text Left
gtk_label_set_xalign (GTK_LABEL(g_Lbl_SysStat), 0);
gtk_label_set_xalign (GTK_LABEL(g_Lbl_LogStat), 0);
gtk_label_set_xalign (GTK_LABEL(g_Lbl_Lbl1), 0);
gtk_label_set_xalign (GTK_LABEL(g_Lbl_Lbl2), 0);
// Add CSS
gtk_style_context_add_provider_for_screen(gdk_screen_get_default(), GTK_STYLE_PROVIDER(cssProvider), GTK_STYLE_PROVIDER_PRIORITY_USER);
// Finish setup and start GUI
g_object_unref(builder);
gtk_widget_show(window);
UpdateDisplay();
gtk_main();
return;
}
// called when window is closed
void on_window_main_destroy()
{
gtk_main_quit();
}
/*------------------END SECTION------------------*/
static void UpdateDisplay(void)
{
ClearLcdDisplay();
gtk_label_set_text(GTK_LABEL(g_Lbl_SysStat), GetSysStat());
gtk_label_set_text(GTK_LABEL(g_Lbl_LogStat), GetLogStat());
return;
}
static void UpdateLcdDisplay(char keyPadValue)
{
if (charCounter >= INPUT_LIMIT)
ClearLcdDisplay();
else
{
inputBuffer[charCounter] = keyPadValue;
charCounter++;
}
gtk_label_set_text(GTK_LABEL(g_Lbl_Lcd), inputBuffer);
return;
}
static void ClearLcdDisplay(void)
{
memset(inputBuffer, 0, 6);
charCounter = 0;
gtk_label_set_text(GTK_LABEL(g_Lbl_Lcd), inputBuffer);
return;
}
/*------------------ EVENT HANDLERS ------------------*/
void on_btn0_clicked(void) {UpdateLcdDisplay('0');}
void on_btn1_clicked(void) {UpdateLcdDisplay('1');}
void on_btn2_clicked(void) {UpdateLcdDisplay('2');}
void on_btn3_clicked(void) {UpdateLcdDisplay('3');}
void on_btn4_clicked(void) {UpdateLcdDisplay('4');}
void on_btn5_clicked(void) {UpdateLcdDisplay('5');}
void on_btn6_clicked(void) {UpdateLcdDisplay('6');}
void on_btn7_clicked(void) {UpdateLcdDisplay('7');}
void on_btn8_clicked(void) {UpdateLcdDisplay('8');}
void on_btn9_clicked(void) {UpdateLcdDisplay('9');}
void on_btnClear_clicked(void) {ClearLcdDisplay();}
void on_btnEnter_clicked(void) {UpdateDisplay();}
void on_btnLogin_clicked(void)
{
LoginLogout(inputBuffer);
UpdateDisplay();
return;
}
void on_btnArm_clicked(void)
{
ArmDisarm();
UpdateDisplay();
return;
}
Here is the code for the alarm. Note, this is just a prototype, I will be using the wiringPi library once I get this interrupt thing figured out.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "Alarm.h"
// Private Function Prototypes
static int PasswordIsCorrect(char* pswAttempt);
// Global Variables
static int armed = 0;
static int loggedIn = 0;
static int PasswordIsCorrect(char* pswAttempt)
{
const char PASSWORD[] = "123";
if (!strcmp(pswAttempt, PASSWORD))
return 1;
else
return 0;
}
/*
* Returns a string,
* Used to update label
*/
char* GetSysStat(void)
{
if(armed)
return "Armed";
else
return "Disarmed";
}
/*
* Returns a string,
* Used to update label
*/
char* GetLogStat(void)
{
if(loggedIn)
return "Logged In";
else
return "Logged Out";
}
void ArmDisarm(void)
{
if (loggedIn && armed)
armed = 0;
else if(loggedIn && !armed)
armed = 1;
return;
}
void LoginLogout(char* pswAttempt)
{
if(PasswordIsCorrect(pswAttempt))
loggedIn = 1;
else
loggedIn = 0;
return;
}
Thank you all for your time!