Generating precise delays with timers in Embedded C

Introduction

Timers help us wait for exact amounts of time in embedded systems. This is useful when we want to control things like blinking lights or reading sensors at steady intervals.

Blink an LED on and off every second.

Create a delay before reading a sensor to let it stabilize.

Generate a precise time gap between sending data packets.

Control motor speed by timing pulses.

Measure how long an event takes to happen.

Syntax

Embedded C

void Timer_Init(void);
void Timer_Start(void);
void Timer_Stop(void);
void Timer_Delay_ms(unsigned int ms);

Timer_Init sets up the timer hardware with the right settings.

Timer_Delay_ms uses the timer to wait for the given milliseconds precisely.

Examples

Initialize the timer and wait for 1 second using the delay function.

Embedded C

Timer_Init();
Timer_Delay_ms(1000); // Wait 1 second

Start the timer to measure time, then stop it when done.

Embedded C

Timer_Start();
// Do something
Timer_Stop();

Sample Program

This program simulates a timer delay function that waits for 5 milliseconds. It shows how to initialize, start, and stop a timer to create precise delays.

Embedded C

#include <stdint.h>
#include <stdbool.h>

// Simulated hardware registers for timer
volatile uint32_t TIMER_COUNT = 0;
volatile bool TIMER_FLAG = false;

void Timer_Init(void) {
    TIMER_COUNT = 0;
    TIMER_FLAG = false;
    // Setup timer hardware here (prescaler, mode, etc.)
}

void Timer_Start(void) {
    TIMER_COUNT = 0;
    TIMER_FLAG = false;
    // Start timer hardware counting
}

void Timer_Stop(void) {
    // Stop timer hardware
}

void Timer_Delay_ms(unsigned int ms) {
    Timer_Start();
    while (TIMER_COUNT < ms) {
        // In real hardware, TIMER_COUNT increments every 1 ms by timer interrupt
        // Here we simulate by incrementing manually for demonstration
        TIMER_COUNT++;
    }
    Timer_Stop();
}

#include <stdio.h>

int main(void) {
    Timer_Init();
    printf("Starting delay...\n");
    Timer_Delay_ms(5); // Delay 5 ms
    printf("Delay finished after 5 ms\n");
    return 0;
}

Important Notes

Real embedded timers count automatically using hardware clock signals.

Delays using timers are more accurate than simple loops because they use hardware.

Always initialize timers before using them to avoid unexpected behavior.

Summary

Timers help create exact wait times in embedded systems.

Use timer start, stop, and delay functions to control timing.

Precise delays improve control over hardware like LEDs and sensors.

Practice

1. What is the main purpose of using timers in embedded C programming for delays?

easy

A. To create precise and accurate wait times without blocking the CPU

B. To increase the CPU clock speed automatically

C. To store large amounts of data temporarily

D. To handle user input events directly

Solution

1. Step 1: Understand timer functionality

   Timers count clock pulses to measure time intervals precisely without busy-waiting.

2. Step 2: Identify timer use for delays

   Using timers allows the program to wait exact times while freeing CPU for other tasks.

3. Final Answer:

   To create precise and accurate wait times without blocking the CPU -> Option A

4. Quick Check:

   Timers = precise delays [OK]

Hint: Timers count clock pulses for exact delays [OK]

Common Mistakes:

• Thinking timers speed up the CPU
• Confusing timers with memory storage
• Assuming timers handle user input

2. Which of the following is the correct way to start a hardware timer in embedded C?

easy

A. beginTimer();

B. start_timer();

C. timer_start();

D. initTimer();

Solution

1. Step 1: Recognize common timer function names

   Standard embedded C libraries often use timer_start() to begin timers.

2. Step 2: Check syntax correctness

   timer_start(); is a valid function call matching typical timer APIs.

3. Final Answer:

   timer_start(); -> Option C

4. Quick Check:

   Correct timer start syntax = timer_start() [OK]

Hint: Look for standard function names like timer_start() [OK]

Common Mistakes:

• Using incorrect function names like start_timer()
• Confusing initialization with starting
• Missing parentheses in function calls

3. Given the code snippet:

timer_set(1000); // Set timer for 1000 ms
timer_start();
while(!timer_expired()) {
  // wait
}
LED_toggle();

What happens after this code runs?

medium

A. LED toggles immediately without delay

B. LED toggles after approximately 1 second delay

C. LED never toggles because timer_expired() is always false

D. LED toggles after 1000 CPU cycles, not milliseconds

Solution

1. Step 1: Understand timer_set and timer_start

   The timer is set for 1000 milliseconds and then started to count down.

2. Step 2: Analyze the while loop waiting for timer expiration

   The loop waits until timer_expired() returns true, which happens after ~1 second.

3. Final Answer:

   LED toggles after approximately 1 second delay -> Option B

4. Quick Check:

   timer_set(1000) = 1 second delay [OK]

Hint: timer_set(ms) delays for ms milliseconds [OK]

Common Mistakes:

• Assuming timer_expired() never becomes true
• Confusing CPU cycles with milliseconds
• Thinking LED toggles immediately

4. Identify the error in this delay code:

timer_set(500);
while(timer_expired()) {
  // wait
}
LED_on();

medium

A. timer_expired() function does not exist

B. timer_set() should be called after the while loop

C. LED_on() should be called before timer_set()

D. The while condition should be !timer_expired() to wait correctly

Solution

1. Step 1: Analyze the while loop condition

   The loop waits while timer_expired() is true, but timer just set, so expired is false initially.

2. Step 2: Correct the condition to wait until timer expires

   It should wait while timer is NOT expired, so condition must be negated: !timer_expired().

3. Final Answer:

   The while condition should be !timer_expired() to wait correctly -> Option D

4. Quick Check:

   Wait while not expired = !timer_expired() [OK]

Hint: Wait while timer not expired: use !timer_expired() [OK]

Common Mistakes:

• Using timer_expired() without negation in wait loop
• Calling timer_set() after waiting
• Assuming LED_on() order affects delay

5. You want to toggle an LED every 250 ms precisely using a timer interrupt. Which approach is best?

hard

A. Use a timer interrupt set for 250 ms to toggle LED inside ISR

B. Use a busy-wait loop with delay function for 250 ms repeatedly

C. Toggle LED once and never use timer

D. Use a timer interrupt but toggle LED outside ISR only

Solution

1. Step 1: Understand precise timing with interrupts

   Using timer interrupts allows exact timing without blocking CPU.

2. Step 2: Identify best place to toggle LED

   Toggling LED inside the timer ISR ensures it happens exactly every 250 ms.

3. Final Answer:

   Use a timer interrupt set for 250 ms to toggle LED inside ISR -> Option A

4. Quick Check:

   Timer ISR toggles LED precisely every 250 ms [OK]

Hint: Toggle LED inside timer ISR for precise periodic delay [OK]

Common Mistakes:

• Using busy-wait loops causing CPU blocking
• Toggling LED outside ISR losing timing precision
• Not using timer interrupts for periodic tasks