The file-descriptor is set not to block or wait, right? How long does it take to get a response back before you can call read? (It has to be received and buffered by the kernel, through system hardware interrupts, before you can read() it.) Have you considered using select() to wait for something to read()? Perhaps with a timeout?ĭo you need the DTR/RTS lines? Hardware flow control that tells the other side to send the computer data? e.g.Please note: If you try to run the executable on a machine with no comms port in the Device Manager, it will crash. I will when I have chance, correct this! To get around this, please ensure a Communication Port is available in Device Manager. Just because you don't use ^Q/^S or hardware flow control doesn't mean the other side isn't expecting it.ģ) Most likely: Add a 'usleep(100000) after the write(). Odds are something is incorrect in there. write( USB, 'init ', 5) Ģ) Double check the serial port configuration. Std::cout << 'Response: ' << response << std::endl ġ) I'd add a /n after init. Std::cout << 'Read nothing!' << std::endl Std::cout << 'Error reading: ' << strerror(errno) << std::endl It was definitely not necessary to write byte per byte, also int n_written = write( USB, cmd, sizeof(cmd) -1) worked fine. Open Port int USB = open( '/dev/ttyUSB0', O_RDWR| O_NOCTTY ) I've solved my problems, so I post here the correct code in case someone needs similar stuff. Complete code needs to work in a real-time environment (specifically OROCOS) so I don't really want sleep-like function. Reported one is only an excerpt of my code. Btw, waiting or usleep() is something I need to avoid. Just for a try, I've created a waiting loop until data is avaliable, but my code never exit the loop. I've tried using select() but nothing happens. I've also tried avoiding the O_NONBLOCK flag on reading, but then I only block until forever. Int USB = open( '/dev/ttyUSB0', O_RDWR| O_NONBLOCK | O_NDELAY ) #include // POSIX terminal control definitions #include // UNIX standard function definitions

Here's my code: #include // standard input / output functions Both commands and response are ASCII characters.Įverything works fine using GtkTerm but, when I switch to C programming, I encounter problems. I need to send those commands and read device's response. I'm working on Linux (Ubuntu).īasically, I am connected to a device which is listening for incoming commands. I'm trying to send/receive data over an USB Port using FTDI, so I need to handle serial communication using C/C++.

C serial port example