USB 2.0 is actually 480Mbit On Tue, Dec 9, 2014 at 2:56 AM, William Hermans <[email protected]> wrote:
> Never really tested g_serial speeds myself, but I can tell you that > g_ether is better than 100Mbit. Somewhere around 170Mbit and even better > for some people. So long as you use a real Linux host. Anyhow, my point is > the hardware is fast enough. > > > I will say is that *if* your Linux desktop is actually in a Windows > virtual machine, your performance issues have nothing to do with the BBB + > software, and everything thing to do with the virtual machine + Windows. > > On Mon, Dec 8, 2014 at 11:36 PM, ivo welch <[email protected]> wrote: > >> >> I am looking for more information on running "Serial over USB" from a >> linux desktop host to the BBB device. Some information on the web seems >> out of date, at least on debian 7.7. other information is very helpful. I >> am summarizing here some of what I have learned myself first: >> >> a sending desktop linux can send information to the BBB over >> /dev/ttyACM0. >> a recipient BBB linux can receive information on /dev/ttyGS0 . >> this is part of the g_multi kernel module and thus works out of >> the box on debian 7.7. >> >> this can be tested as >> >> bbb# cat /dev/ttyGS0 >> >> desktop# echo "hello" > /dev/ttyACM0 >> >> and the bbb should now echo "hello". the comm is buffered, although I am >> not sure on which side (desktop or bbb). this is obvious from looking at >> the desktop immediately after a fresh boot: >> >> desktop# cat /dev/ttyACM0 >> >> which will still return the log in information from the boot on the first >> use. after the buffer is full, the device blocks and waits. >> >> information about the port settings can be found (and potentially set, >> though I don't think anything is needed) with >> >> stty -F /dev/ttyGS0 -a >> >> however, I believe that some of this are just "pretend you are rs232" >> wrong. this is because I just wrote a little perl program that sends >> 1Mbyte into the device and then closes. this takes about 1.5 seconds. >> This would suggest a raw speed of about 7 Mbaud, a little bit faster than >> the 9.6 Kbaud that stty tells me. I am guessing that the "serial port over >> USB" uses the USB 1.1 "full-speed" protocol that caps out at 12 Mbaud. I >> believe hi-speed 480 Mbaud connections require block operations. >> >> the serial comm speed is interesting to compare to the usb mass storage >> speed. A dd from the desktop host to the mounted BBB mass-storage device >> partition over USB produces 21 Mbaud. so, the serial connection is about >> 1/3 of what the BBB is capable of over hi-speed USB mass storage. the eMMC >> limits out at about 70Mbaud local, which is itself about three times the >> speed of the mass storage driver over the USB 2.0 connection. (and remember >> that USB 2.0 is itself limited to 480Mbaud. I also tried to measure the >> speed over the usb0 ethernet with dd and netcat [nc] to see how close this >> could get, but I failed.) >> >> hope this helps. >> >> * one question: I have lost some information sent forth and back, which I >> believe is due to the bbb issuing (from /var/log/syslog) a >> [email protected] time over, scheduling restart >> is it possible to force ttyGS0 to always be available, and never to want >> to restart? >> >> * I may write a different driver that sits on top of the mass storage >> driver and communicates over a small shared storage area. it's a crazy >> idea, but it could be faster than serial-over-usb if I know that I will be >> dealing in blocks of 512 bytes and relatively easy to debug and synchronize. >> >> >> -- >> 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 [email protected]. >> For more options, visit https://groups.google.com/d/optout. >> > > -- 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 [email protected]. For more options, visit https://groups.google.com/d/optout.
