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
2)
On the pc-in-a-box-unit, following are some diagnostics that I could think of ::
lsmod | grep usb
usbnet 37829 1 qmi_wwan
mii 13654 1 usbnet
usb_wwan 19306 1 qcserial
usbhid 47035 0
hid 95946 3 i2c_hid,hid_generic,usbhid
usbserial 38972 8 qcserial,pl2303,usb_wwan
lsmod | grep pl2303
pl2303 18516 0
usbserial 38972 8 qcserial,pl2303,usb_wwan
3)
The USB-Serial-to-RS232 converter information ::
lsusb
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 007: ID 1199:68a2 Sierra Wireless, Inc.
Bus 001 Device 005: ID 05e3:0608 Genesys Logic, Inc. USB-2.0 4-Port HUB
Bus 001 Device 004: ID 413c:2107 Dell Computer Corp.
Bus 001 Device 003: ID 046d:c05a Logitech, Inc. M90/M100 Optical Mouse
*Bus 001 Device 002: ID 067b:2303 Prolific Technology, Inc. PL2303 Serial Port*
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
4)
The checksums of the following drivers are identical on the
pc-in-a-box unit and my-laptop ::
cksum /lib/modules/3.16.0-30-generic/kernel/drivers/usb/serial/usbserial.ko
425603799 59904
/lib/modules/3.16.0-30-generic/kernel/drivers/usb/serial/usbserial.ko
cksum /lib/modules/3.16.0-30-generic/kernel/drivers/usb/serial/pl2303.ko
1987618250 25036
/lib/modules/3.16.0-30-generic/kernel/drivers/usb/serial/pl2303.ko
Behaviour remains same if I disable all USB 3.0 support in pc-in-a-box
unit via ::
USB3.0 Support [Disable]
XHCI Hand-Off [Disable]
EHCI Hand-Off [Enabled]
XHCI Mode [Disable]
USB 2.0(EHCI) Support [Enabled]
*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")?*
I have witheld pc-in-a-box unit details, kindly ask me if specifying
the brand would make any difference.
Will be thankful for any architectural pointers.
Thanks and Regards,
Ajay
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