Hello,
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.
Exactly! That's why/where I was confused. I asked our hardware guys the same thing - a little conflicting information in 2 places. But, they told me that since "Bus-powered hubs are required to have power switches", and our hub isn't bus powered, it's OK. But, I wasn't convinced.
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
So, to be USB2.0 compliant:
In wHubCharacteristics, D1 D0 should never be 1X. I will see what I can do with the hardware.
Will there be any problem, if I just do it in driver (as I said earlier - by modifying wHubCharacteristics) instead of modifying the hardware? Will it break something?
Thanks.
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