[ltp] Cardbus USB2 card for Thinkpad X30

[Richard Neill]

Simon Williams wrote:

> 
> I'm pretty sure this is a myth. Even if the cardbus socket doesn't have 
> a current limiter, the USB card should have. The USB standard only 
> requires that USB ports provide 500mA. Lots of ports are limited to 
> this, including: the motherboard ports on my PC, the front panel on my 
> PC, my USB hubs without the power adapters attached, and my T23's 
> docking station port.

BUT...

* Some ports cannot actually provide the full 500 mA.

* The 500mA limit is only an advisory one. Compliant devices should
   only draw 100 mA (and then request up to 500, which may or
   may not be granted). Some USB controllers will restrict badly behaved
   hardware; in most cases though, the 5V rail is protected only by a
   fuse, and the connected device can draw what it wants.

* Many of the cheap "USB desktop gadgets" such as fans and cup-warmers
   are not compliant, and will happily suck 1A or greater.

* I did some USB power stuff once, and, while testing, accidentally 
shorted the USB port. No permanent harm done, but I instantly crashed
the computer.


Richard