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Signal handling for 3 serial interrupt.

Hi all,

I have 3 different devices Dev1, Dev2 & Dev3 connected to UART 1, UART 2 & UART 3 respectively. I am using these 3 devices alternatively.

I want to write signal handler for these 3 devices interrupts. I am able to handle one signal handler at a time.

But problem is that when I have tried to write signal handler for other (means two signal handler at a time for SIGIO signal), my programs does not work.

Can anybody tell me how to solve this problem?

Please help me.



  • woboyle
    woboyle Posts: 501
    You can only have one handler for each signal at any particular time. You could use sigqueue() and pass some information in the sigval structure that indicates which port generated the interrupt. Then, your handler can determine what to do with the port in question.
  • Thanks for your suggestion.

    I have also one more problem in signal handling. I have connected a GPRS modem to UART1 (serial port).
    In the code i am just sending "AT" command continuously and trying to check its reply. But problem is that sometimes I get reply "OK" and sometimes not.

    Also after some time my code is does not get interrupted even though there is reply from modem.. I have checked this using Hyper Terminal.

    Please help me out what is the prolem?
  • woboyle
    woboyle Posts: 501
    Without seeing your code, I can't say what is your problem, and then I might not be able to determine what's going on. Please explain exactly what you are trying to do. There may be some conflict with system software that is detecting the GPRS modem and trying to connect with it, resulting in some sort of race condition.
  • sbm143
    sbm143 Posts: 9

    In the source code I am just sending "AT" command and trying to check its "OK" response.

    My code is....
    #include <sys/types.h>
    #include <sys/stat.h>
    #include <fcntl.h>
    #include <termios.h>
    #include <stdio.h>
    #define BAUDRATE 	B9600
    #define Modem		"/dev/ttyAM1"
    #define _POSIX_SOURCE 1 /* POSIX compliant source */
    #define FALSE 0
    #define TRUE 1
    /********************************************  Functions Prototype  *****************************************************/
    void Modem_Interface(void);
    void sig_handler(int status);
    void serial_cnfg(void);
    void modemdelay(void);     
    void modemdelay1(void);
    /*************************************************  Structures  **********************************************************/
    struct termios oldtio,newtio;
    struct termios oldtio1,newtio1;
    /**********************************************  Global Variables  *******************************************************/
    int FD_Printer, FD_Modem, FD_CM;
    unsigned char sig_flag;
    int data;
    int fd,cashfd,c, res,cntr=0,virus=0;
    unsigned int CM_rply_Cntr=0;
    char CM_rply_Buf[250];
    char rx_data,rx_cntr=0;
    void sig_handler(int status)
    void modemdelay(void)
    	unsigned int i=0,j;
    void modemdelay1(void)
    	unsigned int i=0,j;
    void serial_cnfg(void)
    	struct sigaction sa;
    	sa.sa_handler	= sig_handler;
    	sa.sa_flags	= 0;
    	sa.sa_restorer	= NULL;
    void Modem_Interface(void)
    	char cmd[]="AT",data,enter=0x0D;
    	unsigned int i=0;
    	printf("Transmitting \n");
    int main(void)
    	unsigned int i;
    	  FD_Printer = open(Printer, O_WRONLY | O_NOCTTY );                 
            if (FD_Printer <0) {perror(Printer); exit(-1); }
    	  FD_Modem = open(Modem, O_RDWR | O_NOCTTY );                 //for modem
            if (FD_Modem <0) {perror(Modem); exit(-1); }
            bzero(&newtio, sizeof(newtio));
            newtio.c_cflag       = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
            newtio.c_iflag 	     = IGNPAR; 
            newtio.c_oflag 	     = 0;
            newtio.c_lflag       = 0;   /* set input mode (non-canonical, no echo,...) */
            newtio.c_cc[VTIME]   = 2;   /* inter-character timer unused */
            tcflush(FD_Modem, TCIFLUSH);
            //printf("\nIn Modem_Interface");
        	  return 0;

    I am using wavecom GPRS ( Q24PL002) modem, with 9600 baud rate. I am setting everything in while loop beacuse whenever i used while(1) for only command transmission after some time signal handler did not worked.
  • 1.Are you able to receive data properly? i mean only receiving data packet from your GPRS device?

    i have done a program for my project exactly the same way which you want ?
    its working for fine N0 HARDWARE control
    see the file attached [file name=serail.txt size=2624]http://www.linux.com/media/kunena/attachments/legacy/files/serail.txt[/file]
  • sbm143
    sbm143 Posts: 9
    1.Are you able to receive data properly? i mean only receiving data packet from your GPRS device?

    Not always. But sometimes i get "AT" reply from modem.I have tested this code on Hyper Terminal (instead of GPRS modem) it works fine. Sometime it also fails.
  • how frequent you are sending AT command ?
  • sbm143
    sbm143 Posts: 9
    Not exactly but nearly about after every 6-9 seconds i am sending "AT" command
  • Hi

    have you done a loop test in serial port (short 2 and 3 pin )
    write data in serial port and check are you getting the data in your signal handler .

    if it works fine then your program is ok

    then go for device .
  • sbm143
    sbm143 Posts: 9
    Yes i have tested my code without modem also. It works fine.


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