Author Topic: usb device(S) timing ?  (Read 609 times)

ulao

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usb device(S) timing ?
« on: August 20, 2018, 07:36:35 am »
I need to get some technical data on how the host deals with mutilate device and this is all I can dig up.
Quote
the host is only ever talking to one endpoint at any given time, it cycles between them so fast that you can't tell it's doing it.
That's fine but hardly helpful. Is there a simple answer or a page that explains this in detail? If we are talking about a multi-plexing of sorts then that implies for each 127 devices, each device timing slows down. By that I can only assume control transfers will slow down. This also implies that each device has to answer all data to see if it's address is being requested.

What's worse is if I put my scope on the usb wires out of the hub no data shows on the wires unless I remove all but 1 device. Though, with all devices they work just fine. Not sure I understand that sorcery yet .

Jan Axelson

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Re: usb device(S) timing ?
« Reply #1 on: August 20, 2018, 09:45:52 am »
The host controller allocates bandwidth according to transfer type and requested bandwidth. My USB Complete book's chapter "A Transfer Type for Every Purpose" also discusses this.