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? thanks, greg k-h -- 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
