Re: why I cannot use C-Media USB Sound device when it's plugged on hub together with other devices?
- From: 张韡武 <zhangweiwu@xxxxxxxxxx>
- Date: Sat, 28 Oct 2006 13:59:40 +0800
于 Fri, 27 Oct 2006 20:34:51 +0000，Scott Alfter写到：
In article <im3a14-smq.ln1@xxxxxxxxxxxxxxxxxxxxx>,
John-Paul Stewart <jpstewart@xxxxxxxxxxxxxxxx> wrote:
[garbled text - line-noise burst?] wrote:
I am pretty interested in this problem: if I wish to use this USB Sound
device on a hub which already have other USB devices plugged in, is it
possible? what should I do?
Does the hub in question have its own power supply? Does the USB sound
device have its own power supply? If the answer to both of those is
"No", then it's possible that the USB bus simply cannot supply enough
power for the hub, the sound device, and the other devices. I forget
how much power is available for so-called "bus powered" devices, but it
isn't much.
2.5W (500mA @ 5V), and that's only if the device tells the host it is a
"high-power" device. If it doesn't, the most current it should pull is
100mA.
If I had to guess, a hub won't bother negotiating for high power because
it's capable of running as a self-powered device with the (usually included)
wall wart. If the combined current draw of the hub, mouse, and headset
exceeds 100mA, the host might not like that.
Thank you very much for this prompt information. I also tried to power the
USB Hub with separate power adapter, the strange behavior of my USB Sound
Device seems not directly related to power, a.k.a. it still doesn't work
when USB Hub is powered separately, and it won't work if the volumn is
turned to minimum (mute) to save power.
.
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