Hi Greg, On Tue, Feb 27, 2018 at 8:57 AM, Brent Sink <brent.sink@xxxxxxxxx> wrote: > On Tue, Feb 27, 2018 at 7:47 AM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: >> On Tue, Feb 27, 2018 at 07:26:23AM -0500, Brent Sink wrote: >>> Hi Greg, >>> >>> On Tue, Feb 27, 2018 at 4:16 AM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: >>> > On Mon, Feb 26, 2018 at 10:05:35PM -0500, Brent Sink wrote: >>> >> Hello, >>> >> >>> >> I'm trying to debug a problem I'm having with a usb-serial device >>> >> (modem) when it's plugged into a USB port on a custom i.MX6 board. >>> >> >>> >> If I connect a USB to Serial converter (I'm using Prolific PL2303), >>> >> and I short the RX and TX lines together so I read back what I write, >>> >> I've noticed that I can send data correctly, but when I receive data >>> >> it is missing the LSB. I've verified this by using a logic analyzer >>> >> to make sure that when I type "A", the logic analyzer also reads "A". >>> >> But when looking at the echo from minicom, it shows "@" instead. "B" >>> >> = "B", "C" = "B", "D" = "D", "E" = "D", and so on. This same problem >>> >> happens to the 3G and 4G modems, as they create ttyACMx ports and >>> >> ModemManager is unable to talk to them because of this same issue. >>> >> This happens on every board we had made, and I've tried using both >>> >> Buildroot and Debian in case it was a rootfs issue... it's not. I >>> >> also tried using a 3.14 kernel and 4.1.15 kernel - same problem exists >>> >> in both versions. >>> > >>> > This sounds like you have a problem with your physical loopback device. >>> > I suggest getting a different one and trying that out. >>> > >>> > good luck! >>> > >>> > greg k-h >>> >>> I'm not sure I understand what you mean by the physical loopback >>> device? Do you mean the Prolific PL2303 device, or the modem, or >>> something else? >> >> What ever you are using to "loop" the TX/RX lines together. Usually >> this is a little "loopback" dongle that you plug into the device. Make >> sure that is stable and works well. It seems that no matter what type >> of device you plug yours into, it does not work, are you sure you have >> all of the needed lines connected? Can you point me in the direction to debug this problem? Perhaps there is a lower level driver that I need to look at why the data is echoed back incorrectly? >> >> thanks, >> >> greg k-h > > > > -- > -brent -- -brent -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
