Hi Daniel,
I think the reply will be the same for RTL & RTAI users :-).
On Thu, Jun 29, 2000 at 08:31:15PM -0500, daniel sheltraw wrote:
> Hello RTAIers
>
> Would someone please write me a code snippet which shows the proper
> usage of the select function when used to wait for data to be sent to a fifo
> from kernel-space.
man select is your best friend.
> Does select to a busy-wait?
Waiting depends on the last parameter of select function. I think the
waiting is active (ie other processes are run).
Some chunks of my code (messy, not exactly what you want, it's about
writing to a fifo from user space, easy to modify):
----------------------------------
static int fifo_0;
static struct timeval timeout={0,10000}; // timeout fifo operations
static fd_set fds; // for select (fifo)
static char *str="/dev/rtf0";
static void openFifo()
{ if((fifo_0=open(str,O_WRONLY))==-1) // open fifo
{ fprintf(stderr,"fifo open %s, %s\n",str,strerror(errno));
exit(0); // if failed
}
atexit(closeFifo);
}
static void closeFifo()
{ close(fifo_0);
}
void writeFifo(int code)
{ int j;
FD_ZERO(&fds);
FD_SET(fifo_0,&fds);
if((j=select(fifo_0+1,NULL,&fds,NULL,&timeout))>0) // if OK to write
{ if((j=write(fifo_0,(char *)&code,sizeof(int)))!=sizeof(int))
{ fprintf(stderr,"writeFifo/write returned %d, %s\n",j,strerror(errno));
exit(0);
}
}
else
{ fprintf(stderr,"writeFifo/fifo not ready for write, %d chars written\n",j);
exit(0);
}
}
-----------------------------------
Regards,
pa
--
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Pavel Andris | tel: +421 7 5941 2167
Institute of Control Theory and Robotics | fax: +421 7 5477 6045
Slovak Academy of Sciences |
Dubravska cesta 9 | e-mail: [EMAIL PROTECTED]
SK - 842 37 Bratislava |
Slovakia |
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