[maemo-developers] USB Host - Class 1 Bluetooth

[From: Charles Werbick]

Hello All,

If I'm out of frame here let me know. But it does seem that a powered
hub would resolve the issue quite nicely. There may also be a software
hack also that allows the kernel to ignore the power requirements. I
do remember seeing power assesment code, in the musb driver source.
However, disabling that check in the kernel is a *bad* idea. Real USB
OTG hardware is used to receiving signals down the +V pin. (That's how
it sends host-peripheral negotiation). So a host->host hookup is
unlikely to destroy OTG hardware, but non-compliant hardware could
theoretically get fried. I'm unfamiliar with the 770 hardware and
whether it is fully OTG compliant or not. But a hub is the safest bet.

cheers,
Charles Werbick


On Mon, Jun 16, 2008 at 5:22 PM, Daniel Blackburn
<daniel at carbonbasedgames.com> wrote:
> I don't think the power should be an issue as Bluetooth adapters
> shouldn't be much more demanding that other USB devices that people have
> got working with the 770.  I am using a circuit similar to this one,
> http://www.hcilab.org/projects/nokia770/nokia770.htm. I will test my
> circuit with other simpler USB devices with comparable power usage but I
> think the problems will be more related to software than hardware. I
> don't have much experience with drivers on Linux so that is the bit were
> I am worried I might have overlooked something crucial.
>
> Cheers,
> Dan
>
> Allen Brown wrote:
>> This is tangential to what you are asking about, but I think you
>> could run into a problem with your power injector. It's been a
>> few years since I read the USB specs, but as I recall the host
>> knows, and makes decisions based on, what power is available.
>> Also it switches that power on and off depending on what state
>> the "bus" is in.  There could be problems if the actual power
>> doesn't match what the host thinks it is.
>>
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