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Old 06-08-2017, 09:32 PM   #1
Registered: Sep 2007
Posts: 237

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Blocked Read N bytes from UART


I want to read from ttyS0 TBD bytes. I need that my thread will be blocked for TBD seconds till I receive all N bytes.

So I used the following code:

m_Handle = open( "ttyS0", O_RDWR);
fd_set set;

timeout.tv_sec = 5;
timeout.tv_usec = 0;

FD_ZERO(&set); // clear the set
FD_SET(m_Handle, &set); // add our file descriptor to the set

rc = select(m_Handle + 1, &set, NULL, NULL, &timeout);
rc = read(m_Handle, pData, Size);

Will this do the work ?

Thank you,
Old 06-09-2017, 07:55 AM   #2
Registered: Mar 2011
Location: USA
Distribution: MINT Debian, Angstrom, SUSE, Ubuntu, Debian
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In the future, recommend you use [code][/code] tags around your code to make it more readable.

Without adding that to a test program and running it myself, my review of it tells me that it "should" work as intended.

However the select() call is specifically for checking file handles, as well as blocking entirely, forget timeouts, until you have new data.

I suspect that you may respond citing that you need to run the thread to do other things. If so, then you are doing too much in this thread and need a different thread to do other work.

You use select() to tell you when you have data available. You use the read() to read that data.

Next you may cite that you don't wish to read incomplete data from the UART.

If so then my opinion is that your receive parser should be message agnostic and should be capable of processing any number of bytes. It should process at the byte level first in a state machine and then dispatch full messages off to another logic level which deals with the message oriented data.

Those are just some guesses as to why you feel you need this architecture. Perhaps you can share a bit more to clarify why you feel this is needed.

And the other question I have is when you ask if it will work or not, ... sorry, but you haven't tried it already?


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