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[ts-7000] Serial port COM2 blocking/nonblocking

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Subject: [ts-7000] Serial port COM2 blocking/nonblocking
From: "Mike Jubes" <>
Date: Wed, 19 Jan 2011 10:24:06 -0000
Considering the recent posts on COM2 processing, I am having an odd problem 
when setting VIM and VTIME on the tc attributes structure. 

I find that on a read() I can get the call to block, or not block at all. But I 
can't get it to time out.

e.g.

If I set: 
        newtio.c_cc[VMIN]  = N;
        newtio.c_cc[VTIME] = 0;
Read will block until N characters are received, this is as expected. 

However, if I set: 
        newtio.c_cc[VMIN]  = N;
        newtio.c_cc[VTIME] = M;

Read will still block until N characters are received, but the timeout (m/10 
seconds) never happens (even when at least one characters are received) This is 
not expected behaviour.

Similarly, if I set: 
        newtio.c_cc[VMIN]  = 0;
        newtio.c_cc[VTIME] = M;

Read() returns non-blocking with no data (This is not expected behaviour, the 
call  should block and return after M/10 seconds) 

Any ideas? 


Oddly enough, I have tried the above on the console COM1 (STDIN) and it works, 
i.e. I can get the timeouts on input to work properly! 

PS I have modified /etc/inittab so that COM2 is not enabled as a console. 






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