更改C全局变量 [英] Changing a global variable in C
问题描述
我正在一个AVR芯片上的C程序。每当串行信号的一声，它运行串行中断ISR（USART_RX_vect）。在这种方法中，应该打开更改 = 1; 。然后在我的主，而循环，应该清除LCD，并显示它，然后设置变化= 0 试。
这是阻止它继续做calulations，并在LCD上显示结果一分钟一百万次。</ P>
然而，当中断方法改变改变变量为1，它似乎并没有改变它全球，并在主要方法总是0 ..
有在这儿有点东西，是用于调试目的。
/ * LCD DEFINES * /
LED的#define PB5
＃定义output_low（端口，针）端口和放大器; =〜（1 <<;＆LT;针）
＃定义output_high（端口，针）端口| =（1 <<;＆下;针）
＃定义set_input（PORTDIR，PIN）PORTDIR＆安培; =〜（1 <<;＆LT;针）
＃定义set_output（PORTDIR，PIN）PORTDIR | =（1 <<;＆LT;针）/ * UART串行DEFINES * /
＃定义F_CPU 16000000UL
＃定义波特率9600
＃定义MYUBRR F_CPU / 16 /波特1＃定义STARTCHAR'R'
＃定义则EndChar'E'字符阅读;
CHAR INPUTBUFFER [12];
焦炭readStatus;
uint8_t有位置;
INT变化;焦炭产量;
INT结果;轴结构
{
uint8_t有axisNumber;
uint16_t位置;
uint16_t oldPosition;}轴1，轴，轴3;
/ *设置UART * /无效USART_Init（unsigned int类型UBRR）
{
/ *设置波特率* /
UBRR0H =（unsigned char型）（UBRR＆GT;＆GT; 8）;
UBRR0L =（unsigned char型）UBRR; / *启用接收器和发射器* /
UCSR0B =（1 <<;＆下; RXEN0）|（1 <<;＆下; TXEN0）; / *设置帧格式：8data，2stop位* /
UCSR0C =（1 <<;＆下; USBS0）|（3';＆下; UCSZ00）;
}无效USART_Transmit（unsigned char型数据）
{
UDR0 =数据;
}unsigned char型USART_Receive（无效）
{
返回UDR0;
}/ ******************* **************** /INT主要（无效）
{
/ * INITALISE SERIAL * /
USART_Init（MYUBRR）; / *打开接收完成中断* /
UCSR0B | =（1 <<;＆下; RXCIE0）; / *开启全局中断* /
SEI（）; 位置= 0;
变化= 0; / *初始化LCD * /
lcd_init（LCD_DISP_ON）; / *初始化显示，光标关闭。 * /
lcd_clrscr（）;
lcd_puts（就绪）; //开启LED 13
set_output（PORTB，LED）;
output_low（PORTB，LED）; 而（1）/ *无限循环* /
{
如果（其他城市== 1）
{
//如果不读书，显示在LCD显示屏上的结果。
axis1.position =（INPUTBUFFER [0]＆下;＆下; 8）| INPUTBUFFER [1];
axis2.position =（INPUTBUFFER [2]＆下;＆下; 8）| INPUTBUFFER [3];
axis3.position =（INPUTBUFFER [4]＆下;＆下; 8）| INPUTBUFFER [5]; CHAR axis1Printout [12];
CHAR axis2Printout [12];
CHAR axis3Printout [12]; sprintf的（axis1Printout，％U，axis1.position）;
sprintf的（axis2Printout，％U，axis2.position）;
sprintf的（axis3Printout，％U，axis3.position）; 焦炭产量[40] =;
strcat的（输出，axis1Printout）;
strcat的（输出，axis2Printout）;
// strcat的（输出，axis3Printout）; lcd_clrscr（）; / *清除屏幕* /
lcd_puts（输出）;
_delay_ms（300）;
变化= 0;
}
}
}/ * *中断/ISR（USART_RX_vect）
{
变化= 1;
无符号字符输入= USART_Receive（）; 如果（输入=='R'）
{
readStatus = 0; //读
位置= 0;
}
否则，如果（（输入='E'）及！及（位置＆LT; 12）及及（位置-1个））
{
INPUTBUFFER [位置] =输入;
位置++;
}
否则，如果（输入=='E'）
{
readStatus = 1; //停止阅读
位置= -1;
output_high（PORTB，LED）;
}
}
您需要使用volatile关键字来声明的变化：
挥发性INT变化;
这告诉了两个线程（主执行循环，你的ISR code）不缓存在寄存器中的值，但总是从内存中获取它。
编辑：有与code另一个问题 - 在你的主循环，由您设置更改为0的时候，你可能已经有本应触发循环再次运行另一个中断。最简单的，但是，不能保证的解决方法是立即将变为0您检查后直它。正确的方法是使用一个锁 - 但根据您的情况，第一个选项可能会做
I am running a C program on an AVR chip. Whenever a serial signal is heard, it runs the serial interrupt ISR (USART_RX_vect). In this method it should turn on change to = 1;. Then in my main while loop, it should clear the LCD and display it and then set change = 0 again.
This is to stop it continually doing the calulations, and displaying the result on the LCD a million times a minute..
However, when the interrupt method changes the change variable to 1, it does not seem to change it "globally" and in the main method it is always 0..
There is a bit of stuff in here that is for debugging purposes.
/* LCD DEFINES */
#define LED PB5
#define output_low(port,pin) port &= ~(1<<pin)
#define output_high(port,pin) port |= (1<<pin)
#define set_input(portdir,pin) portdir &= ~(1<<pin)
#define set_output(portdir,pin) portdir |= (1<<pin)
/* UART SERIAL DEFINES */
#define F_CPU 16000000UL
#define BAUD 9600
#define MYUBRR F_CPU/16/BAUD-1
#define STARTCHAR 'R'
#define ENDCHAR 'E'
char reading;
char inputBuffer[12];
char readStatus;
uint8_t position;
int change;
char output;
int result;
struct Axis
{
uint8_t axisNumber;
uint16_t position;
uint16_t oldPosition;
} axis1, axis2, axis3;
/* SETUP UART */
void USART_Init( unsigned int ubrr)
{
/*Set baud rate */
UBRR0H = (unsigned char)(ubrr>>8);
UBRR0L = (unsigned char)ubrr;
/*Enable receiver and transmitter */
UCSR0B = (1<<RXEN0)|(1<<TXEN0);
/* Set frame format: 8data, 2stop bit */
UCSR0C = (1<<USBS0)|(3<<UCSZ00);
}
void USART_Transmit( unsigned char data )
{
UDR0 = data;
}
unsigned char USART_Receive( void )
{
return UDR0;
}
/*****************************************************************/
int main(void)
{
/* INITALISE SERIAL */
USART_Init(MYUBRR);
/* Turn on Receive Complete Interrupt */
UCSR0B |= (1 << RXCIE0);
/* Turn On GLobal Interrupts */
sei();
position = 0;
change = 0;
/* Initialise LCD */
lcd_init(LCD_DISP_ON); /* Initialize display, cursor off. */
lcd_clrscr();
lcd_puts("READY");
//Turn on LED 13
set_output(PORTB,LED);
output_low(PORTB,LED);
while (1) /* Loop forever */
{
if (change == 1)
{
//If not reading, display the result on the LCD display.
axis1.position = (inputBuffer[0]<< 8) | inputBuffer[1];
axis2.position = (inputBuffer[2]<< 8) | inputBuffer[3];
axis3.position = (inputBuffer[4]<< 8) | inputBuffer[5];
char axis1Printout[12];
char axis2Printout[12];
char axis3Printout[12];
sprintf(axis1Printout,"%u ", axis1.position);
sprintf(axis2Printout,"%u ", axis2.position);
sprintf(axis3Printout,"%u ", axis3.position);
char output[40] = "";
strcat(output, axis1Printout);
strcat(output, axis2Printout);
//strcat(output, axis3Printout);
lcd_clrscr(); /* Clear the screen*/
lcd_puts(output);
_delay_ms(300);
change = 0;
}
}
}
/* INTERRUPTS */
ISR (USART_RX_vect)
{
change = 1;
unsigned char input = USART_Receive();
if (input == 'R')
{
readStatus = 0; //Reading
position = 0;
}
else if ((input != 'E') && (position < 12) && (position > -1))
{
inputBuffer[position] = input;
position++;
}
else if (input == 'E')
{
readStatus = 1; //Stop Reading
position = -1;
output_high(PORTB,LED);
}
}
You need to declare change using the volatile keyword:
volatile int change;
This tells the two 'threads' (main execution loop and your ISR code) to not 'cache' the value in a register, but always retrieve it from memory.
Edit: There's another problem with the code - in your main loop, by the time you set changed to 0, you may have already had another interrupt which should have triggered your loop to run again. The easy-but-not-guaranteed fix is to immediately set changed to 0 straight after you check it. The proper way would be to use a lock - but depending on your situation, the first option might do.
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