On Mon, Aug 29, 2016 at 05:56:03PM +0530, Ajay Garg wrote: > Hi All. > > We have a PC-in-a-box unit, with 2 COM-ports, 2 USB 2.0 ports and 1 > USB 3.0 port. > We are testing the COM-ports (COM1 and COM2) and the USB-ports. > > We proceeded as follows :: > > a) > In the setup > > User-App <=> COM1 <=> RS232-data <=> RS232-to-RS485 converter <=> > RS485-data <=> Modbus-Device > > when we send a modbus-command from user-app ==> modbus-device, we > receive the modbus-response fine. (Of course, RS232 is enabled for > COM1 in BIOS). > > > b) > If we modify the setup just a bit as > > User-App <=> USB-Port <=> USB-Serial-to-RS232 converter <=> Rs232-data > <=> RS232-RS485 converter <=> RS485-data <=> Modbus-Device > > and then send a modbus-command from user-app ==> modbus-device, we DO > NOT receive even a single byte as response. > > Very surprisingly, if we use the above setup in a USB-port of my > personal laptop, we get the response fine (thereby signifying that > that all elements from USB-Serial-to-RS232 converter <=> Rs232-data > <=> RS232-RS485 converter <=> RS485-data <=> Modbus-Device are fine). > > > Some more facts :: > > 1) > uname -a gives identical output for my-laptop and the pc-in-a-box unit :: > > uname -a > Linux blah-blah-login 3.16.0-30-generic #40~14.04.1-Ubuntu SMP Thu Jan > 15 17:45:15 UTC 2015 i686 i686 i686 GNU/Linux First off, I suggest you get support from the distro you are using, as they are the only ones that can give you that. This is a very old kernel release and nothing that the community can help you out with, sorry. > *So, now my question is that given the OS is identical and all > "OS-drivers" same, what could be the difference in behaviour on > pc-in-a-box and my-laptop? > Are some usb-drivers present at hardware/motherboard level too, thus > making the "difference in hardware" the root-cause (rather than > "difference in software")?* If you are comparing the default use of a usb to serial converter to a serial port on a motherboard, yes, they do sometimes work differently. I would suggest checking your hardware flow control settings, lots of usb-serial devices default to them enabled, while a "uart on a motherboard" defaults to them disabled. Make sure you really are setting everything up identically. If so, try a newer kernel release. Again, 3.16 is really old and obsolete, we can help you out here if you use a 4.7 or newer kernel. thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
