Hi Mike, On Fri, Nov 29, 2013 at 9:56 AM, Mikester <mikester...@gmail.com> wrote: > > > I have a USB FTDI serial device that connects to the BBB and it shows up under /dev/ttyUSB0. > > After bootup If I try connecting to the device via a c program I get an error "11 - Resource temporarily unavailable". > > However, if I first connect to the device using something like "screen" or "minicom" then kill the process, I am able to use my c program to access the serial device without any problems. > > Is there some sort of initialization script I need to run in order to access the USB serial device? > > If I use stty -F /dev/ttyUSB0 -a I get > > speed 230400 baud; rows 0; columns 0; line = 0; > intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>; eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; > rprnt = ^R; werase = ^W; lnext = ^V; flush = ^O; min = 1; time = 0; > -parenb -parodd cs8 -hupcl -cstopb -cread -clocal -crtscts > -ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon -ixoff -iuclc -ixany -imaxbel -iutf8 > opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0 > isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke
I seem to recall that modemmanager and/or brltty (on your host computer) may cause access problems. So one of the first things I do is to uninstall those 2 packages (this may not be what you're running into, but I've been burned by it several times, so I figured I'd mention it). It looks like CLOCAL is turned off, which means that it expects modem control lines to take effect (including carrier detect). I've written a small sample program I call sertest which you can find here: https://github.com/dhylands/projects/blob/master/host/sertest/sertest.c It opens a serial port and takes any characters you type and sends them to the serial port, and prints any received characters to stdout. If you short RxD and TxD on your USB serial dongle, then you should be able to see what you type. Opening the serial port using O_NONBLOCK is desirable (otherwise you may hang if the carrier detect isn't asserted), but it will cause the error that you're seeing when you try to read data from the serial port. You'll see here: https://github.com/dhylands/projects/blob/master/host/sertest/sertest.c#L225 that I turn off the non-blocking behaviour after opening the serial port, which means that the read will block instead of returning EAGAIN. If you're still having issues, it would be useful if you could post the code that you're using. You didn't mention which exact call was returning the EAGAIN error. -- Dave Hylands Shuswap, BC, Canada http://www.davehylands.com -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
