I had a similar issue a few years back with multiple USB cams on a
The fact is, that many USB 'hubs' do not provide separate 'channels',
but a stream using unique ids. Very often not a problem, but it's
conceivable that with a serial/USB converter a seperate hub is required.
You can test this easily enough if you plug one converter into the 'hub'
and another into the PC USB port locally. Basic PCs have two or more
seperate USB channels, and are easily upgraded using a pci usb card (=
even more independant channels).
The power suggestion by Robert is also a very common USB issue. If this
is the problem, and you have the option, you should power the 'hub'
locally . I have managed to run 4 webcams at a distance of over 24m from
the PC by using this solution.
Just a thought, but if this is a critical app, you may want to consider
installing pci-card based serial ports anyway. You can extend R232 comm
lines up to at least 18m without problems, maybe more. This would also
resolve any problems caused by USB device allocation randomness at
On Thu, 2006-12-14 at 08:47 +0000, Robert Fitzsimons wrote:
> Hello Mick
>> Did you get this issue resolved? I'm wondering if it's a power problem,
> are the GSM modems powered by the USB hub? If so maybe the hub can't
> provide enough power for all of the modems. You could try plugging in
> another hub in and putting half the modems into this new hub.
>> On Tue, Dec 12, 2006 at 01:27:42PM -0000, Mick wrote:
> > How is everyone?
> > I'm looking for some help with the following problem ...
> > I'm working away on an issue with GSM modems connected via a Serial to USB
> > cable to a 7 port Belkin hub.
> > When I connect one of the GSM modems I'm told that usbserial.c: PL-2303
> > converter now attached to ttyUSB0. When I run the following command
> > rm /dev/modem ; ln -s /dev/ttyUSB0 /dev/modem ; minicom
> > I can connect to the modem without any difficulty and issue at commands to
> > it.
> > I then go to connect the second modem to the hub and get the message as
> > listed below. I'm having a lot of trouble getting all of these modems up and
> > running and any help that anyone can give me would be sincerely grateful.
> > Thanks in advance,
> > Mick
> > usbserial.c: PL-2303 converter now attached to ttyUSB1 (or usb/tts/1 for
> > devfs)
> > usb.c: serial driver claimed interface c292fde0
> > hub.c: port 3, portstatus 100, change 0, 12 Mb/s
> > hub.c: port 4, portstatus 100, change 0, 12 Mb/s
> > hub.c: port 5, portstatus 100, change 0, 12 Mb/s
> > hub.c: port 6, portstatus 100, change 0, 12 Mb/s
> > hub.c: port 7, portstatus 100, change 0, 12 Mb/s
> > Unable to handle kernel NULL pointer dereference at virtual address 00000014
> > printing eip:
> > c01cf9f4
> > *pde = 00000000
> > Oops: 0000
> > CPU: 0
> > EIP: 0010:[<c01cf9f4>] Not tainted
> > EFLAGS: 00010006
> > eax: c11e4600 ebx: c3aad820 ecx: 00000001 edx: 00000000
> > esi: c11fb360 edi: c3aad820 ebp: 00000292 esp: c3807e80
> > ds: 0018 es: 0018 ss: 0018
> > Process minicom (pid: 801, stackpage=c3807000)
> > Stack: c3aad820 c11fb360 00000286 c3aad824 c01d078b c3aad820 c3aad820
> > 00000000
> > c11b924c 00000000 c237281c c2372874 00000001 c01c700d c3aad820
> > c487c480
> > c3aad820 c487d20d 00000001 c237281c c2aa6000 c01d24b7 c237281c
> > c03f18c0
> > Call Trace: [<c01d078b>] [<c01c700d>] [<c487c480>] [<c487d20d>]
> > [<c01d24b7>][<c01d2575>] [<c0185f6f>] [<c015a060>] [<c0149d31>]
> > [<c018636f>] [<c0136d3c>][<c01353cd>] [<c013544e>] [<c010737b>]
> > Code: 8b 52 14 83 ea 1c 8b 42 04 8b 5a 08 25 00 00 00 2f 0d 00 00
> > --
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