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USB Power Draw non-compliant?

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magicJack Apprentice

Joined: 30 Mar 2008
Posts: 10

PostPosted: Sat May 03, 2008 7:09 pm    Post subject: USB Power Draw non-compliant?

It seems that many magicJack users have USB-related issues. Often marginal power-supplies or a borderline USB system are blamed. Suggested solutions are to try a different port, or maybe a (DC Adapter) powered USB hub. While of course it works for many, there seem to be too high a percentage of USB issues. Could the following be the cause?

USB Hubs are powered through two methods:

1) self-powered, where there's a dedicated power supply. EACH port from this hub-type can consume up to 500mA. Root hubs are powered from the computer's power supply, and therefore are self-powered, as are add-on hubs powered by a DC adapter.

2) bus-powered, where the power is drawn through the bus. Since it originates from a 500mA port connection, maximum power consumed by the entire hub is constrained to 500mA. USB current is allocated in units of 100mA & the hub itself consumes one of these 100mA units, leaving a maximum of 400mA remaining to supply all the devices connected to the hub. This bus-powered method is generally fine only for connecting lower-powered devices such as mice or keyboards, or where the device has its own power cord.

To determine the current being drawn from a USB hub, start the Device Manager & look under the USB controllers section to find the listed hubs. Each listed hub's Properties dialog contains a "Power" tab which lists the attached devices & their USB power requirements, along with the remaining ports available.

The magicJack, being powered solely via the USB bus, clearly should not consume more than 500mA. Yet if you inspect the Properties dialog of the "Generic USB Hub" installed for MJ, you'll see the following:

- USB Mass Storage Device (98mA)
- TigerJet USB Composite Device (500mA)

That's 598mA of listed devices, plus if it truly is operating as a multi-device hub, you can add another 100mA required for the hub itself, totalling nearly 700mA of power requirements. How does it get past the bus-powered USB constraints? By somehow tricking the system, advertising itself as self-powered instead of bus-powered. I could be wrong about all this, but it seems like this non-compliance could be a major factor in all the USB issues.

Also, by design, if a system senses Power Overload it can shut down the hub to avoid burning out the circuitry. However, it would seem the MJ "trick" to appear as self-powered might defeat this safety measure, and possibly expose the USB circuitry to overload damage?

Personally, I don't have issues the 1st time installing MJ to a different USB port, as the process of installing the devices seems to cause everything to be recognized. And it's generally reliable when connected during the Windows boot process, rarely causing trouble at that time. But if I stop the USB MJ device and later reconnect during the same Windows session, it rarely recognizes the "TigerJet USB Composite Device". Lot's of disconnecting/reconnecting, hanging up the non-robust Windows Explorer & menu system, etc., and I might be able to eventually have all the MJ components recognized, but it's generally easiest to just reboot the system. The behavior on my system works similarly whether from root hubs or DC-adapter-powered multi-port hubs.

(WinXP SP2)
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magicJack Apprentice

Joined: 30 Mar 2008
Posts: 10

PostPosted: Mon Jun 09, 2008 11:09 pm    Post subject: My USB Issue Resolved

After reading a post by Stewart, I tried using the XP Device Manager to Disable the YMAX "fake" CD-ROM drive. This immediately stopped the USB issues I had whenever reconnecting the MJ to the USB port.

I don't know why I would need the YMAX drive since I also bypass the annoying MJ Splash Screen by using the direct launcher shortcut as described elsewhere in the forum:
"C:\Documents and Settings\username\Application Data\mjusbsp\magicJack.exe" /foreground /scf _magicJackPersonalDataRoot "F:\magicJack"

However, for some reason I found that the MJ softphone wouldn't properly register while the YMAX drive was disabled, so to avoid USB issues I had to go through the annoying cycle of :

- Disable the YMAX drive prior to disconnecting MJ from USB
- Re-Enable the YMAX drive *after* re-connecting MJ to USB

(Once the softphone is running, the YMAX drive can be disabled without impacting performance.)

Finally, I found a better solution:

Examination of the YMAX drive Properties "Details" tab in the Device Manager showed "Class Upper Filters" for Nero7 InCD. These filters seem to apply to every device in the DVD/CD-ROM drive Class. I figured that the filters were incompatible with the "fake" CD-ROM drive, so I uninstalled InCD (which I really have no use for anyway). Problem solved! No more need to Disable\Enable the YMAX drive - I can just leave it Enabled, and all the USB functions of the MJ work properly after every USB connection. So that may be one reason why Nero is on the "doesn't play nice with MJ" list. I do still have Nero7 installed, just not the related InCD component, and everything now works very well.
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