Re: [tlug] USB Hub v Power Injector: The Mostly Unimportant Differences

[jep200404@example.com]

On Thu, 10 Jan 2013 15:26:52 +0800, Stephen Lee <sl-tlug@example.com> wrote:

> Do you know if a usb hub is supposed to be intelligent? 

The essence of the I-O Data device, its connector block 
(which is not a hub) is likely just plastic and metal. 

USB hubs are complicated beasts that need a complicated IC. 
They mix power, analog, and digital logic. 

> Is it supposed
> to shut off ports like you say hosts does, or tell hosts how much
> current it can supply so hosts can tell it to shut off which port etc?

Both. 

USB hubs are required to monitor power consumption of the 
devices that are plugged into them and limit (shut off) 
current to offending devices. See "Over-current Protection" 
and "Power switching"sections on page 353 of Chapter 17, 
"Managing Power" in the first edition of "USB Complete" by Jan 
Axelson. It's much easier to read than the official USB spec.