hi alan:
2014-02-14 23:36 GMT+08:00 Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>:
> On Fri, 14 Feb 2014, vichy wrote:
>
>> hi Alan:
>>
>> > I don't understand your question.
>> >
>> > At full speed (12 Mb/s), the time required to transfer 188 bytes is
>> >
>> > (188 bytes) * (8 bits/byte) / (12 b/us) = 125.33 us,
>> >
>> > which is greater than 125 us.
>>
>> @@ -1412,7 +1412,7 @@ sitd_slot_ok (
>> */
>> uf = uframe & 7;
>> if (!tt_available(ehci, period_uframes >> 3,
>> - stream->udev, frame, uf, stream->tt_usecs))
>> + stream->udev, frame, uf, stream->usecs))
>>
>> if so, shall we modify code like above?
>> Use transfer time instead of bus budget to calculate tt_avaiable?
>
> No. stream->usecs is the time required on the high-speed bus, and
> stream->tt_usecs is the time required on the full/low-speed bus.
>
> tt_available makes its decisions based on whether there is enough
> available time on the full/low-speed bus. Therefore it needs to use
> stream->tt_usecs.
it makes me a little confused.
if we try to send 108 bytes to FS iso ep over HS hub.
shouldn't we use below formula to calculate what bus time need for?
NS_TO_US (think_time + usb_calc_bus_time (
dev->speed, is_input, 1, 108));
it seems no matter we transfer 108, 118, 140, even 188 bytes to FS iso
ep over HS hub.
The full/low bus time are all the same.
appreciate your help
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