Ngắt trong vi điều khiển là gì?
Ngắt (interrupt) là quá trình dừng chương trình chính đang chạy để ưu tiên thực hiện một chương trình khác, chương trình này được gọi là chương trình phục vụ ngắt (ISR – Interrupt Service Routine). Sau khi thực hiện xong chương trình phục vụ ngắt thì vi điều khiển quay lại thực hiện tiếp công việc trước đó.
Ngắt trong Arduino
AVR có ít nhất 2 timer. Từ atmega8 trở đi là có 2 timer 8bit và 1 timer 16 bit. Chip Atmega2560 trên board Arduino Mega có 2 (8bit) + 4 (16bit) = 6 Timer. Arduino không hỗ trợ thư việc cho việc ngắt timer, vì thế chúng ta sẽ dùng thư việc của 1 bên thứ ba (third-party)
Download thư viện tại: download
Chi tiết thư viện: Timer One Libary
Download thư viện Timer Three
Ví dụ:
#include <TimerOne.h> // khai báo thư viện timer 1 void setup() { pinMode(13,OUTPUT); Timer1.initialize(1000000); // khởi tạo timer 1 đến 1 giây Timer1.attachInterrupt(Blink); // khai báo ngắt timer 1 } void loop() { } void Blink() { digitalWrite(13,!digitalRead(13)); //trình phục vụ ngắt đảo mức logic cho chân số 13 }
Chia sẻ thêm:
TimerOne and TimerThree let you use the built-in 16 bit timers.
Hardware Requirements
These libraries use Timer1 and Timer3.
Each timer controls PWM pins. While uses these libraries, analogWrite() to those pins will not work normally, but you can use the library pwm() function.
Basic Usage
The timer is configured to repetitively measure a period of time, in microseconds. At the end of each period, an interrupt function can be run. The PWM pins can also be configured to switch during a portion of the period.
If using TimerThree, replace “Timer1” with “Timer3”.
Configuration
Timer1.initialize(microseconds);
Begin using the timer. This function must be called first. “microseconds” is the period of time the timer takes.Timer1.setPeriod(microseconds);
Set a new period after the library is already initialized.
Run Control
Timer1.start();
Start the timer, beginning a new period.Timer1.stop();
Stop the timer.Timer1.restart();
Restart the timer, from the beginning of a new period.Timer1.resume();
Resume running a stopped timer. A new period is not begun.
PWM Signal Output
Timer1.pwm(pin, duty);
Configure one of the timer’s PWM pins. “duty” is from 0 to 1023, where 0 makes the pin always LOW and 1023 makes the pin always HIGH.Timer1.setPwmDuty(pin, duty);
Set a new PWM, without reconfiguring the pin. This is slightly faster than pwm(), but pwm() must be used at least once to configure the pin.Timer1.disablePwm(pin);
Stop using PWM on a pin. The pin reverts to being controlled by digitalWrite().
Interrupt Function
Timer1.attachInterrupt(function);
Run a function each time the timer period finishes. The function is run as an interrupt, so special care is needed to share any variables beteen the interrupt function and your main program.Timer1.detachInterrupt();
Disable the interrupt, so the function no longer runs.
Example Program
#include <TimerOne.h> // This example uses the timer interrupt to blink an LED // and also demonstrates how to share a variable between // the interrupt and the main program. const int led = LED_BUILTIN; // the pin with a LED void setup(void) { pinMode(led, OUTPUT); Timer1.initialize(150000); Timer1.attachInterrupt(blinkLED); // blinkLED to run every 0.15 seconds Serial.begin(9600); } // The interrupt will blink the LED, and keep // track of how many times it has blinked. int ledState = LOW; volatile unsigned long blinkCount = 0; // use volatile for shared variables void blinkLED(void) { if (ledState == LOW) { ledState = HIGH; blinkCount = blinkCount + 1; // increase when LED turns on } else { ledState = LOW; } digitalWrite(led, ledState); } // The main program will print the blink count // to the Arduino Serial Monitor void loop(void) { unsigned long blinkCopy; // holds a copy of the blinkCount // to read a variable which the interrupt code writes, we // must temporarily disable interrupts, to be sure it will // not change while we are reading. To minimize the time // with interrupts off, just quickly make a copy, and then // use the copy while allowing the interrupt to keep working. noInterrupts(); blinkCopy = blinkCount; interrupts(); Serial.print(“blinkCount = “); Serial.println(blinkCopy); delay(100); }
Interrupt Context Issues
Special design is necessary to share data between interrupt code and the rest of your program.
Variables usually need to be “volatile” types. Volatile tells the compiler to avoid optimizations that assume variable can not spontaneously change. Because your function may change variables while your program is using them, the compiler needs this hint. But volatile alone is often not enough.
When accessing shared variables, usually interrupts must be disabled. Even with volatile, if the interrupt changes a multi-byte variable between a sequence of instructions, it can be read incorrectly. If your data is multiple variables, such as an array and a count, usually interrupts need to be disabled for the entire sequence of your code which accesses the data.
Details
New development on TimerOne occurs on this Github page: 1 2
