c++ - AVR - 中断 vector 和全局变量

Question

我正在使用 ATmega32 每 32 毫秒中断一次以执行一些任意操作，这目前并不重要。
我正在使用 timer0 的定时器溢出来中断，它可以预测和完美地工作。

我的问题是我有一个全局变量:

volatile int isSampling;

那没有被写入中断 vector 。我读到整数需要 volatile 才能消除编译器优化的可能性，但我将其声明为 volatile 并且它仍然无法正常工作。

#include <AVR/IO.h>
#include <util/delay.h> 
#include <avr/interrupt.h>

char studentID[12]            = {'S',1,2,3,4,5,6,7,'A','B','C','D'};

char buffer[72]; //Max bitlength = 6. * studentID length
char repcount[72];
int pointer;

volatile int isSampling;

void setup(void);
void startup(void);
void loadValue(unsigned char loadedValue);
void processValue(unsigned char processedValue, short bitLength);
void sendDot(void);
void sendDash(void);



int main(){

    setup();
    while(1)
    {

        if (isSampling == 1){
            startup();
            int i;
            for (i = 0; i < 12; i++){
                loadValue(studentID[i]);
                //Flash lights after letter sent.
                _delay_ms(500);
                PORTB = 0xF0;
                _delay_ms(500);
            }
        }
    }   
}

void setup(void){
    DDRB = 0xFF;
    sei();  
    TCCR0 = TCCR0 | 0x05;                   
    TIMSK|=(1<<TOIE0);  
    TCNT0 = 0;
    pointer = 0; 
    isSampling = 1;
}

ISR(TIMER0_OVF_vect)
{   
    //Every 32ms this interrupt vector is called.
    isSampling = 0;
}

void startup(void){
    //Play LED startup pattern
    int i;
    for (i = 0; i < 4; i++){
        PORTB = 0b11110011; //Bit 5 is constantly sampled. 4 is output
        _delay_ms(250);
        PORTB = PORTB & 0x00;
        _delay_ms(250);
    }
    _delay_ms(500);
    _delay_ms(500);
}

void loadValue(unsigned char loadedValue){
    switch (loadedValue){
        case   1: processValue(0b01111000, 5);
        case   2: processValue(0b00111000, 5);
        case   3: processValue(0b00011000, 5);
        case   4: processValue(0b00001000, 5);
        case   5: processValue(0b00000000, 5);
        case   6: processValue(0b10000000, 5);
        case   7: processValue(0b11000000, 5);
        case   8: processValue(0b11100000, 5);
        case   9: processValue(0b11110000, 5);
        case   0: processValue(0b11111000, 5);
        case 'A': processValue(0b01000000, 2);
        case 'B': processValue(0b10000000, 4);
        case 'C': processValue(0b10100000, 4);
        case 'D': processValue(0b10000000, 3);
        case 'E': processValue(0b00000000, 1);
        case 'F': processValue(0b00100000, 4);
        case 'G': processValue(0b11000000, 3);
        case 'H': processValue(0b00000000, 4);
        case 'I': processValue(0b00000000, 2);
        case 'J': processValue(0b01110000, 4);
        case 'K': processValue(0b10100000, 3);
        case 'L': processValue(0b01000000, 4);
        case 'M': processValue(0b11000000, 2);
        case 'N': processValue(0b10000000, 2);
        case 'O': processValue(0b11100000, 3);
        case 'P': processValue(0b01100000, 4);
        case 'Q': processValue(0b11010000, 4);
        case 'R': processValue(0b01000000, 3);
        case 'S': processValue(0b00000000, 3);
        case 'T': processValue(0b10000000, 1);
        case 'U': processValue(0b00100000, 3);
        case 'V': processValue(0b00010000, 4);
        case 'W': processValue(0b01100000, 3);
        case 'X': processValue(0b10010000, 4);
        case 'Y': processValue(0b10110000, 4);
        case 'Z': processValue(0b11000000, 4);
        case '.': processValue(0b01010100, 6);
        case ',': processValue(0b11001100, 6);
        case '?': processValue(0b00110000, 6);
        case '!': processValue(0b00110000, 5);
        case ':': processValue(0b11100000, 6);
        case '=': processValue(0b10001000, 5);
    }
}

void processValue(unsigned char processedValue, short bitLength){
    unsigned char result;
    int i;
    //Enter Loop at the length of bits in numerical morse code
    for (i = 0; i < bitLength; i++){
        result = processedValue & 0x80;
        processedValue = processedValue << 1;
        if (result) sendDash();
        if (!result) sendDot();
        _delay_ms(1000);
    }
}

void sendDot(void){
    //Send Dot
    PORTB = 0x05;
    _delay_ms(250);
    PORTB = 0x00;
}

void sendDash(void){
    //Send Dash
    PORTB = 0x06;
    _delay_ms(750);
    PORTB = 0x00;
}

好的，我已经找到导致问题的违规代码，但我不确定它导致问题的原因。 当我从主 while 循环中删除 loadValue(studentID[i]) 时，代码按预期工作。但是当我把它放回去时，它又坏了。

Answer 1

如 Oli Charlesworth 所述，_delay_ms(500) 行导致了问题。如果设置为高(超过 250 毫秒)，_delay_ms() 函数可能会导致不可预测的行为。