Re: XHCI, "brain-dead scanner", and microframe rounding

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On 06/30/2014 05:43 PM, Alan Stern wrote:
> On Mon, 30 Jun 2014, Mathias Nyman wrote:
> 
>> xhci specs says it needs the interval rounded to nearest 2^(X) value,
>> which would be 256, not 128. I'll take a look at that.
> 
> Doesn't the spec says it needs the interval rounded _down_ to a
> power of 2?
> 

So it does, xhci 6.2.3.6 
"software shall round the computed value of Endpoint Context Interval field down to the nearest base 2 multiple.."

Seems quite brutal to round 255 to 128 instead of 256.
I guess its better to schedule a transfer too often than not enough

-Mathias

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