On Sat, 12 Mar 2005, abcd efgh wrote:
> Alan,
>
> Thanks for educating me!
>
> I thought the driver deciphers it by reading a logic circuit that says what
> is available. I read the data sheet of ISP1521BE (USB hub controller that we
> use), and it looks like you have to play with the pins to properly set
> up/configure the hub. So, the manufacturer/assembler *can* make a mistake. I
> guess that's the problem I'm facing.
Seems likely.
> But, the thing is the same hub was and even now, works fine with 2.4.23
> without any change in the driver. Is it because, 2.6.x is more stringent in
> enforcing standards?
It's not a question of enforcing anything. In 2.4 the hub driver always
tries to turn on power to hub ports, even for hubs that don't support
power switching (which doesn't make much sense). The hub driver in 2.6 is
smarter and only turns on port power for hubs that do support power
switching.
Since your hub claimed that it doesn't support power switching, naturally
it never got turned on under 2.6.
> Guess, my interpretation of "1X is used only on those 1.0 hubs that
> implement no power switching" is wrong. Apart from specs, is power switching
> reqd for the working of USB2.0? I appreciate any pointers for a good source
> of information. I want to know if this requirement is there just because it
> is in (or not "not in") specs or is it reqd for the actual working of USB
> 2.0.
No, power switching isn't necessary. It even says so in the spec,
section 11.11 (which you should read in full):
Self-powered hubs may have power switches that control delivery of
power downstream facing ports but it is not required. Bus-powered
hubs are required to have power switches.
The spec goes on to say that even when power switching isn't available,
the hub must still implement the Logical Power Switching Mode field in
wHubCharacteristics. So the two low-order bits shouldn't be set to 10.
Alan Stern
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