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?
>
>> > For each packet (token, data, and handshake), the overhead includes
>> > inter-packet delay, cable delay, SYNC, bit-stuffing, and End-Of-Packet
>> > -- all in addition to the PID, token, and CRC bytes.
>> >
>> > I don't know where you got that "13" from. If you assume the
>> The 13 bytes I see is from usb spec section 5.8.4.
>
> Then you must have noticed the sentence just above Table 5-9:
>
> The table does not include the overhead associated with bit
> stuffing.
>
> The table also doesn't include the overhead associated with cable
> delay and intermediate hubs.
>
>> > inter-packet delays always require 1 byte time and count up the
>> > inter-packet delays (3), SYNCs (3), token bytes (3), PID and CRC hytes
>> > (3), and handshake (1), that adds up to 13 bytes of protocol overhead.
>> > But it leaves out cable delay, bit-stuffing, and End-Of-Packet signals.
>> >
>> > You also have to remember that the spec allows the clock rate on
>> > Full-Speed devices to vary by up to 0.25% of the nominal rate.
>> so you mean FS speed will be 12M bits/s +- 30000 bits/s?(30000/12M = 0.25%)
>
> That's right. Also, Low-Speed devices are allowed to vary by up to
> 1.5%, and High-Speed devices are allowed to vary by up to 0.05%.
Appreciate your help,
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