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Date: Tue, 10 Apr 2012 20:39:35 +0200
From: Peter Rosin <peda AT lysator DOT liu DOT se>
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Subject: Re: Problem with reading nonblocking /dev/com in 1.7.10 and up
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On 2012-04-10 20:17, Abdul Muis wrote:
> I have notice that I could not read serial device (/dev/com4 or
> /dev/ttyS3) with non blocking mode since 1.7.10 and up. I used to read
> serial data while doing openGL visualization. In which, the openGL
> display was not changed due to blocking mode reading.
> 
> The command is
> 
> fcntl(fd, F_SETFL, FNDELAY); // set reading as non blocking mode, should
> return '0' if no data comming
> n=read(fd, &test, 10); // starting from 1.7.10 always return -1 although
> there is incoming data

I don't know and haven't tried lately (no serial ports connected at the
moment), but in the past I have successfully used:

	long flags = fcntl(fd, F_GETFL);
	fcntl(fd, F_SETFL, flags | O_NONBLOCK);

FNDELAY is probably a non-posix name that in practice is equivalent to
O_NONBLOCK, but more importantly I think you should OR the flag in without
clobbering all other flags.

However, I last tested that before 1.7.10, so my version may well behave
just like your code.

Cheers,
Peter

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