Linux - Multiple Serial Port Communication with C

Question

I have a device with multiple serial ports that I am programming with embedded linux and I would like to communicate over these two ports simultaneously and asynchronously.

I know how to write to one serial port such as:

bytes_sent = write( fd, &(string[i]), 1 );

But that's to only one serial port

do I use the termios struct and the c_cflags to differentiate ports? As you can see it's a little vague, I'm just kind of diving in and getting my feet wet with this, any general help to point me vaguely in the right direction will help.

I thought fd either returned 1 or -1 for success/fail. So if that's the case fd would be assigned its own integer ID? — user1257629, Jun 05 '13 at 17:50
so if I made an fd1 and fd2 file descriptor (and each had their own integer number) I could potentially write/read to two ports? — user1257629, Jun 05 '13 at 17:53
Yes. Different serial ports are considered as different peripherals, and can work independently using their own descriptors. — ZeWaren, Jun 05 '13 at 18:20
`fd` doesn't "return" anything. It's an integer. Do you mean `open()`? — Carl Norum, Jun 05 '13 at 18:25

score 5 · Accepted Answer · answered Jun 05 '13 at 18:33

How did you get the file descriptor for your first serial port? Assuming it was something like:

fd = open("/dev/serialPort0", O_RDWR);

You should just be able to do:

fd2 = open("/dev/serialPort1", O_RDWR);

And get a file descriptor to use for the other serial port. Write to each however you'd like:

char str1[] = "Hello, port 1!\n";
char str2[] = "hello, port 2!\n";

write(fd, str1, sizeof str1);
write(fd2, str2, sizeof str2);

score 1 · Answer 2 · edited May 23 '17 at 12:01

1

Please see a related answer to configure the port to the desired speed, parity, and i/o blocking characteristics.

Even if the hardware has 4 or 24 serial ports, proper handling is to treat each individually and independently.

edited May 23 '17 at 12:01

Community

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answered Jun 11 '13 at 16:23

wallyk

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If we have two serial ports A and B , think about server client communication is there any way to connect thoose two ports in order to send messeges ? – gregni Feb 09 '21 at 19:22
@nikos.grigoriadis: Sure. Are ports A and B on the same machine? What is the topology? – wallyk Feb 11 '21 at 07:12
yeah i want to make an AT command based server and client where they will communicate through seria port and reading writing will be at tty files .Yeah is on the same machine i have to test it with socat but i cant fix it am openning /dev/pts/0 at server and trying to read something through it but i cant make it work .What should i do in client open the same tty file ? or openning /dev/pts/1 ? if i open the pts/1 who to connect them with socat and test when client writing something server reads it and send responce ? If you can help me with this i would appreciate – gregni Feb 11 '21 at 09:02
@nikos.grigoriadis: What does the Linux command `lsusb` show? – wallyk Feb 11 '21 at 17:24

Linux - Multiple Serial Port Communication with C

2 Answers2