So, the COM port on Windows is talking to a virtual serial port in the BBB
USB widget.
There is no hardware UART involved, and no hardware clocks anywhere to
throttle or pace anything.
Then, you push this for transfer rate, while running it under a non
realtime OS.
I guess I am not surprised that you are having problems.
The USB widget is nice for doing simple things, with fast, simple set up
for beginners.
I suspect you are trying to run it in an application where it has not been
well tested.
For a stable system, I would recommend considering doing the data transfer
over a real hardware serial port, or if that is not fast enough, do the
transfer using Ethernet. (And I don't mean Ethernet over USB using the
Widget.)
I find the true hardware serial ports, and the genuine FTDI serial to USB
converters to be stable well above 100,000 bits per second. Some report
success in the megabits per second range, I have just not had to personally
go there, yet.
You never have been specific about how many bits per second of data that
you have to move.
I think that is an important place to start.
--- Graham
==
On Thu, May 4, 2017 at 6:53 PM, Dennis Lee Bieber <wlfr...@ix.netcom.com>
wrote:
> On Thu, 4 May 2017 15:39:43 -0700 (PDT), David Howlett
> <david.howle...@gmail.com> declaimed the
> following:
>
>
> >I plugged the micro USB port on the BBB into my USB hub. The USB hub is
> >currently attached to a windows PC but the same fault happens when the USB
> >cable is plugged into my mac book running OSX.
> >
>
> Which, since there is no FTDI chip on the BBB, is effectively an
> emulated serial port... The USB-serial driver responds to I/O operations as
> if it were a serial port, but things like baud rate are mostly meaningless
> -- the driver moves bytes from the client buffer to the USB buffer, and USB
> transfers at (if USB2.0 full speed -- 480kbps; ignoring the breaks caused
> by USB packet size AND that the host computer has to poll the USB device to
> ask for each packet of data; effective throughput being closer to 250kbps).
>
> And, the Windows (or Mac) side is also an emulated serial, but as
> the
> host side, the USB driver controls the polling of the other end asking for
> data or to send packets.
>
>
> >I have also come to suspect that there are no hardware UARTS involved. I
> >believe that the serial line is being emulated.
> >
>
> Unless you use wires on the UART pins of the BBB, likely true.
> Those
> may be hardware UARTs, but as soon as something is connected that converts
> to USB, the actual data transfer is USB and the other end emulated.
>
> >
> >On the PC side I can set the baudrate to any number. The data rate and the
> >error rate appear to be unaffected. For example:
> >
> >x = serial.Serial('COM10', baudrate=10)
> >x = serial.Serial('COM10', baudrate=9600)
> >x = serial.Serial('COM10', baudrate=100_000_000_000)
> >
>
> As I suspect -- the baud rate is irrelevant when you get into the
> USB
> protocol. At most, it may control a "filter" as to how rapidly the drivers
> relay stuff to the USB protocol. That is -- at slow rates there may only be
> a few bytes of data per USB packet, whereas at really high rates each USB
> packet will contain more data (and hence be more efficient when taking the
> polling overhead into account).
>
> --
> Wulfraed Dennis Lee Bieber AF6VN
> wlfr...@ix.netcom.com HTTP://wlfraed.home.netcom.com/
>
> --
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