4-Port USB Hub

jglen490 · 12-23-2008, 08:53 PM

My ancient warrior, Thinkpad T20, has one USB connector. I bought a Targus 4-port USB hub as a USB port "expander". When I connect it to the laptop, the light on the hub glows, so power is getting to it. When I attach my Zire 31 PDA to sync with Korganizer (running Kubuntu 8.04), the only way the PDA will sync is if I first issue an

Code:

lsusb

on the CLI. Thinking that this was not normal, I removed the USB hub and connected the PDA directly. Within a second or two, the sync process just works. Running

Code:

tail -f /var/log/syslog

without the USB hub shows hald doing its thing correctly and the PDA connects via ttyUSB0 and ttyUSB1, as it should. Running it with the USB hub shows hald not seeing the PDA until I enter

Code:

lsusb

.

Is there a udev rule or something that I need to set up to make the 4-port be automagically recognized?

htnakirs · 12-24-2008, 04:13 AM

Did you try plugging in the hub's auxillary power? Sometimes the hub cannot be adequately powered with just the USB power, so there would be an auxillary power adapter.

archtoad6 · 12-24-2008, 05:01 PM

If the hub works after running lsusb, what could power possibly have to do w/ this problem?

jglen490 · 12-24-2008, 05:28 PM

Quote:

Originally Posted by htnakirs

Did you try plugging in the hub's auxillary power? Sometimes the hub cannot be adequately powered with just the USB power, so there would be an auxillary power adapter.

It's self-powered -- off the USB wire from the laptop.

AuroraCA · 12-24-2008, 05:53 PM

Some devices require that the USB connection be plugged into a primary USB or a powered hub. They comsume too much power for an unpowered hub.

archtoad6 · 12-25-2008, 07:33 AM

htnakirs & AuroraCA,
You both mention inadequate power, a h/w solution, for a problem that already has a manual s/w solution (running lsusb). OP asked for help in configuring his/her system:

Quote:

Originally Posted by jglen490

Is there a udev rule or something that I need to set up to make the 4-port be automagically recognized?

Not to be too rude, but what makes either of you think that extra power will help the hub to be recognized by the system, when it works properly once recognition has been manually triggered w/ lsusb? Please explain or stop suggesting extra power.

Quote:

Originally Posted by jglen490

It's self-powered -- off the USB wire from the laptop.

(Just to be sure.) Does this mean that it has neither an external power supply, nor 2nd USB connector to draw extra power?

AuroraCA · 12-25-2008, 08:09 AM

You can start by referring to the Hub Power section here:

Wikipedia USB Hub

Quote:

A bus-powered hub is a hub that draws all its power from the host computer's USB interface. It does not need a separate power connection. However, many devices require more power than this method can provide, and will not work in this type of hub.

USB current (related to power) is allocated in units of 100 mA up to a maximum total of 500 mA per port. Therefore a compliant bus powered hub can have no more than four downstream ports and cannot offer more than four 100 mA units of current in total to downstream devices (since one unit is needed for the hub itself). If more units of current are required by a device than can be supplied by the port it is plugged into, the operating system usually reports this to the user.

In contrast a self-powered hub is one that takes its power from an external power supply unit and can therefore provide full power (up to 500mA) to every port. Many hubs can operate as either bus powered or self powered hubs.

However, there are many non-compliant hubs on the market which announce themselves to the host as self-powered despite really being bus-powered. Equally there are plenty of non-compliant devices that use more than 100 mA without announcing this fact (or indeed sometimes without identifying themselves as USB devices at all). These hubs and devices do allow more flexibility in the use of power (in particular many devices use far less than 100 mA and many USB ports can supply more than 500 mA before going into overload shut-off) but they are likely to make power problems harder to diagnose.[original research?]

Some powered hubs do not supply enough power to support a 500mA load on every port. For example, many 7 port hubs come with a 1A power adapter, when in fact seven ports could draw a maximum of 7 x 0.5 = 3.5A, plus power for the hub itself. The assumption is that the user will most likely connect many low power devices and only one or two requiring a full 500mA.

jglen490 · 12-25-2008, 12:35 PM

Thank you archtoad6. The USB hub does have an extra USB connector for power, but my laptop has only one USB port. I suspect that power is not an issue as the device connected to the USB hub is a PDA which is self powered. That and I left the PDA connected for a few hours when the battery was initially showing about half power. When I checked later (to see if the PDA was being recognized) the battery meter showed as full -- so power is flowing through the USB hub to the PDA's connector.

To reiterate, when I plug the PDA into the USB hub, my laptop only sees the PDA if I enter an "lsusb" command. When I plug the PDA directly into the laptop's USB port, the PDA is recognized almost instantly. Therefore, I believe that it is the USB port itself that is not being recognized until the "lsusb" command is issued.

So perhaps a udev rule, or something that the hal daemon can use, is needed to properly activate the USB hub. If not, then it's O.K., I can just take a second or two for the "lsusb" command since I always have a konsole open.

Thank you all very much!!