Re: Trouble reading a character device.

["saravanaraj v" <saravanaraj.v@gmail.com>]

Thanks Glynn

On Tue, Dec 16, 2008 at 8:21 PM, Glynn Clements
<glynn@gclements.plus.com> wrote:
>
> saravanaraj v wrote:
>
> >    I am facing few issues in reading from a character device.
> >    I have created few character devices using 'mknod' and I am writing
> > continuously to those devices using 'printk'. After some time I start
> > another process to read from the device. The open/read is done using
> > normal sys calls for file open/reading. I have pasted the code for
> > your ref. When I run this program the read happens for some time and
> > then there is no progress. I am suspecting that  everything written to
> > the device before this program was started is read. The flags I tried
> > for opening the file were RD, RDWR with/without NONBLOCK. The output
> > was same in all the cases. I tried "cu -l /dev/virt_uart8". It was
> > able to read continuosuly without any problem. Can someone tell where
> > the problem is ?
> >
> > int main(){
> >
> > int fd,counter=0;
> > fd = open("/dev/virt_uart8",O_RDONLY|O_NONBLOCK);
> > if(fd<0) printf("\nError in opeining file");
> > while(1){
> >
> >     int nread = 0;
> >     nread = read(fd,buffer,MAX_BUFFER_SIZE-1);
> >     if(nread>0) {
> >         buffer[nread]='\0';
> >         printf("%s",buffer);
> >     }
>
> If you want to print data which doesn't necessarily have a trailing
> newline, you need fflush(stdout) or setvbuf(stdout, NULL, _IONBF, 0).
>
> If you make that change and still have problems, it's likely to be an
> issue with the device. E.g. you may need to disable XON/XOFF
> processing with tcsetattr(), or put the device into raw mode.
>
> --
> Glynn Clements <glynn@gclements.plus.com>