USB Hubs

[jlpoole]

See "Update" below; here is the original posting:

-- start of original posting --
I used a Targus hub ("Targus hub") [not powered] and interposed it between my SheevaPlug and my Verbatim 16 GB thumb drive.  The SheevaPlug constantly reset when the Targus hub was in the chain; at first I figured it was my software and problem with date/time, but I'm now convinced they were not the culprit.  I have since removed the Targus hub and the SheevaPlug, running Gentoo 2.6.30_rc1, has not had a single reset for well over a week.

So, I do not know if the problem I experienced with the hub is hardware related, or software related.  Can others reply with their experiences of using a hub, please indicate your model number and whether it is self-powered?

I'm guessing a hub that provides it's own power may be a better choice so that there are not possible voltage drops.  I'm planning on returning the Targus hub to Office Depot and buying a powered hub.

Maybe having a hub between a thumb drive and the SheevaPlug introduces delays and/or wait states that triggers a crash?

---------------------
The hub is a Targus brand, specifically Targus Micro Travel USB 2.0 4-port hub purchased at Office Depot, model ACH63US, Item No. 10, Serial No. 0811000833. 

-- end of original posting --

Update 4/30/2009 6:18 p.m. PDT

I've been running my plug at work without a USB HUB; however, I have had the serial connector to my laptop (Dell 620) on it and I've found I've been getting resets, again.  I just realized, when I had the plug at home for two weeks where my SheevaPlug ran uninterrupted, the SheevaPlug was running without being connected via a serial connector, all of my access way via network.  So, it is likely that the problems I was experiencing were related to the continuous attachment of the serial cable from my laptop to the SheevaPlug.  I'm running the plug now without the serial cable connected and so far no resets.  Given nobody else is reporting problems with the hubs, I think the concern now should be directed at the stability of having the serial cable connected all the time.


Update 5/4/2009 5:12 a.m. PDT

I've been running my plug at home with the Targus bus and without the serial port connection since Thursday night and I have not had a crash; that's 72 hours up and running.  I've added to the hub a 2nd Verbatim 32 GB drive (my 16 GB drive max'd out when trying some Oracle products) and all is well.

Conclusion the hub was not causing the problem I had -- the serial interface connected to my Dell laptop seems to have to been the problem.

[jlpoole]

It looks like a very careful assessment of the USB capabilties may be in order.  The USB link can be a critical part of a SheevaPlug set up, and if USB components have a variance either in meeting specifications and/or performance, then these facts should be considered when attaching a USB device to the SheevaPlug.  I've been working under the assumption that if a product says it meets USB 2.0 specifications, then everything should work?

Well, a read of http://www.linux-usb.org/FAQ.html has caused me to wonder if I should scrutinize the specifications of USB devices.  For instance:

First, you need to know what kind of USB "Host Controller" hardware you have. Mainstream hardware has one of three kinds, named after the hardware register-level "Host Controller Interface" (HCI) they implement. ...

"Universal" HCI (UHCI) ... doesn't do very much in hardware, which makes the software do more work (and need more memory)
"Open" HCI (OHCI)... does quite a bit more of USB in hardware.
"Enhanced" HCI (EHCI)... the only kind used to talk to high speed devices.

As I indicated in my initial posting, mixing the Targus Hub with a Verbatim thumb drive caused problems.  I've learned Verbatim sells a USB hub (# 95258); however, they do not certify it for Linux.  I have pending an inquiry with Verbatim's customer support asking for an explanation of why they do not certify their drive for Linux.  My thought in buying a Verbatim hub was I might finesse the problem I previously experience by using the same manufacturer's, i.e. Verbatim, components on the hope that they play nicely together.

I'm guessing that a hub has to be a traffic coordinator among its children and the device it is attached to.  I can imagine how problems could arise if everyone doesn't use the same protocol and/or have compatible specifications.  Add to that, the design of the kernel's device driver.

For reference, here's what I found that relates to the USB interface in the 1.0 documentionation,  SheevaPlug Development Kit - Reference Design-Rev. 1.0.pdf:

Figure 1.7: Block Diagram (sheet 10/21) has "Usb 2.0 with Phy interface"

Section 2.8 Drive Connection
USB 1.1 or USB 2.0 are supported

3.4.3 USB 2.0
88F6281 contains a Universal Serial Bus 2.0 port includes an embedded USB 2.0 PHY. The USB interface can support either Host or Device mode. The SheevaPlug design supports HOST mode only. There is no strapping provided by the SheevaPlug board to switch between HOST or DEVICE USB mode.  USB 2.0 port feature 480 Mbps, 12Mbpsm and 1.5Mbps data rate; bit stuff error detection, NRZ bit stuffing, and built in FS/HS termination signaling.

Am I over-analyzing here?  If people have attached hubs and have not had problems, it would be helpful to so indicate.  The lack of response to my initial posting has me wondering if people are not using hubs.

As an aside, I was looking at Corsair's 64 GB thumb drive (Model CMFUSBHC-64GB) on NewEgg's web site and read an interesting comment:

It seems many people don't understand that when transferring Data directly from a USB to USB it's going to be slow regardless what the Flash drive capacity is. My Best advice to you will be to go from Flash Drive to HDD to Flash Drive you will drastically reduce your transfer time. Example: 14gigs of data on a USB Drive would have taken me 3+ hrs transferring directly to USB Drive. It actually took 20 mins Total (12 mins from USB Drive to HDD then 8 mins HDD to USB Drive) . Understand that going from USB to USB is not a ideal way of transferring data.

[kilowatt]

I've been using a cheap USB 2.0 hub I bought here http://www.cablewholesale.com/specs/usb-hub/40u2-42401.htm without any problems at all.

By the way if anyone needs some cables these guys have great prices.  No I don't work for them.

[plugit]

Unpowered USB hubs make me nervous. I know they should work, but...

[kilowatt]

The hub I mentioned has a jack to for using a power supply.  I used it for a few days without a supply.  I rsynced a large harddrive to another and to a flash drive, tested a few usb devices all the while running the file system on one of the usb drives.  No problems.  I'm still using it but now I have a power supply connected to the hub so I don't put any unneeded strain on the internal Plug power supply.

[bfmorgan]

Does it come with a power supply? I checked out the their web site and it did not indicate the port came with a power supply.

Thanks,

[kilowatt]

No it does not come with a power supply.  It has the same small DC power jack as one of my older USB 1.0 hubs.  So, I'm using the power supply from the old hub.  It is rated at DC 5V 2A inner+/outer-.  I'm not sure what the power jack size is but it is the same as a few devices I have with 5V 2A power supplies.

[jmknapp]

Just tried a Targus Bend-A-Hub, $18 from Amazon:

http://www.amazon.com/Targus-ACH103US-4-Port-Bend-Adapter/dp/B00180LGXQ

The hub is powered from the SheevaPlug. I connected a USB hard drive and a USB memory stick, both were recognized.

A Kill-A-Watt power meter doesn't register any difference with the hub connected or disconnected (4 watts total).

Joe

[jlpoole]

here's Verbatim's replay about their USB hub and Linux:

Hi John,
 
Thank you for contacting Verbatim Technical Support.

We are sorry to inform you that we don't support linux operating system. However, the USB hub might work with the linux operating system.

If you need any further assistance please call us on: 646-537-3411 and we will be happy to assist you. 

Thanks and regards,

Verbatim Technical Support

[dg]

Yup, I'm getting these problems as well. Glad it's not just me!

I've tried three hubs; a shiny new D-Link 7-port hub that I bought specifically to use on the SheevaPlug and two cheapo unbranded 4-port hubs from Scan. One of the unbranded hubs appears to be reliable. The other unbranded hub causes I/O errors on high bandwidth stuff. The D-Link hub does USB resets, randomly disconnects and reconnects devices, and occasionally --- when plugging or unplugging it from the machine --- crashes the SheevaPlug.

This is the kind of error I get:

May  1 10:09:25 chur kernel: end_request: I/O error, dev sda, sector 3839
May  1 10:09:25 chur kernel: sd 33:0:0:0: [sda] Result: hostbyte=0x07 driverbyte=0x00

I'm doing RAID via USB, which means I'm way stressing the hubs; but they should still work. They *appear* to be reliable when plugged into a desktop PC, but I haven't done proper testing yet. I'm using the stock Marvell kernel, and I gather that some USB bugfixes have gone into the mainstream kernel since then, so I'm now in the process of upgrading my kernel.

[moridin1138]

I've tried an APC USB hub and a "PowerMate" (cheapo) hub, both powered, and I get either regular disconnects or it doesnt work at all.

Most of the time I get this in dmesg:

Code:

hub 1-1:1.0: cannot reset port 4 (err = -71)
hub 1-1:1.0: cannot reset port 4 (err = -71)
hub 1-1:1.0: cannot reset port 4 (err = -71)
hub 1-1:1.0: Cannot enable port 4.  Maybe the USB cable is bad?
hub 1-1:1.0: cannot disable port 4 (err = -71)
hub 1-1:1.0: unable to enumerate USB device on port 4
hub 1-1:1.0: cannot disable port 4 (err = -71)
usb 1-1: USB disconnect, address 4
hub 1-0:1.0: unable to enumerate USB device on port 1

Any ideas?  Or should I just buy a "known" working hub?

[jlpoole]

I've tried an APC USB hub and a "PowerMate" (cheapo) hub, both powered, and I get either regular disconnects or it doesnt work at all.

<snip>

Any ideas?  Or should I just buy a "known" working hub?

Do the hubs work on other boxes and/or operating systems?
What version of Linux are you running?
Have you had other USB problems?

Are you seeing these messages while connected via the serial port or via an SSH session?

[moridin1138]

Do the hubs work on other boxes and/or operating systems?

Yes, the APC hub works in OSX, Windows and other Linux machines.

What version of Linux are you running?

Ubuntu, technically:

Linux debian 2.6.30-rc4 #4 PREEMPT Fri May 1 08:27:07 MDT 2009 armv5tel GNU/Linux

From this gent:
http://plugcomputer.org/plugforum/index.php?topic=84.0

Have you had other USB problems?

No, the FTDI USB-Serial adapter I am using works great.  I tried using the APC hub unpowered as well, and when I plugged a USB to 1-wire adapter the ports shut off.

[Nicolas]

Just for info I have tried 3 different hubs to run software raid on the usb interface. I'm quite sure that I've stressed the hubs :-)

- trust 420A - 4 ports, powered: completely unreliable and on his way to the trash can;
- LaCie ? - 3 ports + mini usb device: reliable powered or not;
- Belkin F5U700 - 7 ports: reliable powered or not.

Tested on 2 "new" SheevaPlug.

N.

[restamp]

I presume you tested these hubs under an OS, and not under a Uboot, right?

FWIW, I have been using a D-Link 7-port powered hub, a DUB-H7, with good results on my Plug.  It seems the initial kernel that came with the Plug would not recognize it, but all the later Ubuntu kernels have.  Unfortunately, I've yet to find a hub that the Uboot can inter-operate with.