Notes of PhiL    About    Categories    Tags    Archive    Feed    GitHub Repo

UT.6.03x Embedded Systems - Shape the World - Lab 09: Functional Debugging


In chapter 9, I learned about debugging theory, SysTick timer, arrays, and character strings. I also learned how to debug my program effectively using the logic analyzer.

  1. Debugging Theory: This section includes some terminologies and types of debugging.
    When we talk about the quality of a debugger, we talk about its “nonintrusiveness”, which means the characteristic of the debugger that allows the system to operate normally as if the debugger did not exist.
    Other terminologies that I learned from chapter 9 are dump (record info into memory), filter (add conditions to the process of dumping info), monitor (output info on LEDs or LCD). Dump, filter, and monitor are used rather than print statements because they are less intrusive than print statements.
    There are also two methods of debugging, Black-box testing (external observing) and White-box testing (internal observing). Many people only debug their software using Black-box testing (or only White-box testing). Remember, effective debugging uses both of them.

  2. SysTick timer: The SysTick timer has 3 registers inside, which can be viewed as this table below


  1. Clear ENABLE bit to turn off SysTick:

  2. Load initialization to the RELOAD register:

  3. Rewrite some value to CURRENT register:

  4. Write the desired mode to the CTRL register:

For example, let’s take 5000 as the initial value we write on CURRENT register. The SysTick will countdown: 5000, 4999, 4888, …, 3725, …, 2100, …, 1, 0. However, when the SysTick finishes counting down to 1, the Count Flag (bit 16 of the CTRL register) will set 1, which means turning on. As a result, when the SysTick finishes counting down to 0, the value will return back to 5000. The process of counting repeats over and over again.


Note that to be able to run and grade the labs, you have to follow the software requirements. Unfortunately, the software and the course don’t support Linux. However, if you follow the official instruction from Texas Instruments, you can upload and run your program on the LaunchPad.

See below for my code, or view it on my GitHub.

 * UTAustinX: UT.6.03x Embedded Systems - Shape the World
 * Lab 9: Functional Debugging
 * File Name: main.c
 * Description:
 *   Learn how to debug using Logic Analyzer
 *   When either of SW1 and SW2 is pressed, the LED should flash red 10 Hz
 *   Otherwise, turn of the LED
 *   When the LED is flashing red,
 *   dumb data of PF4-PF0 to data[] array for visual observing
 * Compatibility: EK-TM4C123GXL
 * Author: Phi Luu
 * Location: Portland, Oregon, United States
 * Created: March 25, 2016
 * Updated: June 23, 2017

#include "TExaS.h"
#include "tm4c123gh6pm.h"

// Constant declarations to access port registers
// using symbolic names instead of addresses
#define GPIO_PORTF_DATA_R     (*((volatile unsigned long *)0x400253FC))
#define GPIO_PORTF_DIR_R      (*((volatile unsigned long *)0x40025400))
#define GPIO_PORTF_AFSEL_R    (*((volatile unsigned long *)0x40025420))
#define GPIO_PORTF_PUR_R      (*((volatile unsigned long *)0x40025510))
#define GPIO_PORTF_DEN_R      (*((volatile unsigned long *)0x4002551C))
#define GPIO_PORTF_LOCK_R     (*((volatile unsigned long *)0x40025520))
#define GPIO_PORTF_CR_R       (*((volatile unsigned long *)0x40025524))
#define GPIO_PORTF_AMSEL_R    (*((volatile unsigned long *)0x40025528))
#define GPIO_PORTF_PCTL_R     (*((volatile unsigned long *)0x4002552C))
#define PF4                   (*((volatile unsigned long *)0x40025040))
#define PF3                   (*((volatile unsigned long *)0x40025020))
#define PF2                   (*((volatile unsigned long *)0x40025010))
#define PF1                   (*((volatile unsigned long *)0x40025008))
#define PF0                   (*((volatile unsigned long *)0x40025004))
#define GPIO_PORTF_DR2R_R     (*((volatile unsigned long *)0x40025500))
#define GPIO_PORTF_DR4R_R     (*((volatile unsigned long *)0x40025504))
#define GPIO_PORTF_DR8R_R     (*((volatile unsigned long *)0x40025508))
#define GPIO_LOCK_KEY         0x4C4F434B // unlock the GPIO_CR register
#define SYSCTL_RCGC2_R        (*((volatile unsigned long *)0x400FE108))
#define NVIC_ST_CURRENT_R     (*((volatile unsigned long *)0xE000E018))

// Global variables
unsigned long time_counter[50]; // array contains time
unsigned long data[50];         // array contains data

// Function prototypes
void SystickInit(void);
void PortFInit(void);
void Delay(void);
void EnableInterrupts(void); // enable interrupts

int  main(void) {
    // Setup
    unsigned long i = 0, last = NVIC_ST_CURRENT_R;
    unsigned long now;

    // activate grader and set system clock to 16 MHz
    TExaS_Init(SW_PIN_PF40, LED_PIN_PF1);
    PortFInit();        // initialize PF1 to output
    SystickInit();      // initialize SysTick, runs at 16 MHz
    EnableInterrupts(); // enable interrupts for the grader

    // Loop
    while (1) {
        if (!PF4 || !PF0) { // if either SW1 or SW2 is pressed
            PF1 ^= 0x02;    // toggle the red LED

            if (i < 50) {
                now             = NVIC_ST_CURRENT_R;
                time_counter[i] = (last - now) & 0x00FFFFFF; // 24-bit time difference
                data[i]         = GPIO_PORTF_DATA_R & 0x13;  // record changes
                last            = now;

 * Initializes port F pins for input and output
void PortFInit(void) {
    volatile unsigned long delay;

    SYSCTL_RCGC2_R    |= 0x00000020;     // 1) activate clock for Port F
    delay              = SYSCTL_RCGC2_R; // allow time for clock to start
    GPIO_PORTF_LOCK_R  = GPIO_LOCK_KEY;  // 2) unlock GPIO Port F
    GPIO_PORTF_CR_R   |= 0x1F;           // allow changes to PF4-PF0
    GPIO_PORTF_AMSEL_R = 0x00;           // 3) disable analog function
    GPIO_PORTF_PCTL_R  = 0x00;           // 4) PCTL GPIO on PF4-PF0
    GPIO_PORTF_DIR_R  |= 0x0E;           // 5) PF4, PF0 inputs, PF3-PF1 outputs
    GPIO_PORTF_AFSEL_R = 0x00;           // 6) disable alternate function
    GPIO_PORTF_PUR_R  |= 0x11;           // enable pull-up resistor on PF0 and PF4
    GPIO_PORTF_DEN_R  |= 0x1F;           // 7) enable digital I/O on PF4-PF0

 * Initializes the SysTick timer
void SystickInit(void) {
    NVIC_ST_CTRL_R    = 0;          // disable SysTick during setup
    NVIC_ST_RELOAD_R  = 0x00FFFFFF; // maximum reload value
    NVIC_ST_CURRENT_R = 0;          // any write to current clears it
    NVIC_ST_CTRL_R    = 0x00000005; // enable SysTick with core clock

 * Delays the program 50 millisecond (0.05 seconds)
 * @assumption    80-MHz clock
void Delay(void) {
    unsigned long volatile count;

    count = 72727; // 50 millisecond

    while (count) {