UART serial interrupt routine

Question

Is there a simple way to use the registers as an interrupt trigger? I can make the application run in a new pid and poll for serial input using fork() I just need to read data, no write needed This is the "read" code I am using

fd = open("/dev/ttyUSB0", O_RDWR | O_NOCTTY | O_NDELAY);
fcntl(fd, F_SETFL, 0);
char buf[256];
n = read(fd, (void*)buf, 255);

I am not even sure if I have framed the question correctly Could it look something like this?

int  com_data=0;

void main(void)
{
 if (com_data){
  --do something--
 }
}

char getcom()
    {
    retrieve byte from rxbuffer;
    return(byte);
    }

interrupt routine
    {
    com_data=1;
    }

Answer 1

No "interrupt" needed. The "if(com_data)" would be achieved by using poll(2) to test if data is available on fd.

Answer 2

I was going to post this as a comment rather than an answer, but perhaps standalone is better.

It's a long time since I wrote interrupt driver drivers under Linux, so my memory is rusty... these days I'm more native.

There is an article in the Linux How To which talks about using interrupts for serial I/O. Sadly it is a bit RTFM (for setserial), so may not be overly helpful, but may give a pointer or two.

For example, ttyS0 normally uses IRQ number 4 known as IRQ4 (or IRQ 4). A list of them and more will be found in "man setserial" (search for "Configuring Serial Ports").

Further help on setting up interrupt handlers can be found on Linux Device Drivers, another site in my bookmarks.

However, you don't need to use interrupts, if your can manage polling adequately. You just need to configure the port to return (without delay) if no data is available. Replace fcntl(fd, F_SETFL, 0); with fcntl(fd, F_SETFL, FNDELAY);

The call to read() will return immediately with n=0 if no data is available.