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Message
From: Rudolf Usselmann<rudi@a...>
Date: Wed Feb 4 13:54:27 CET 2004
Subject: [usb] endpoints ?
On Wed, 2004-02-04 at 17:34, i_rajesh1@r... wrote:
> Hi all,
> Can anyone help me out with these questions
>
> *Why we need multiple end points other when (1 EP0,1 TxEP and a 1 RX
> EP) will do ??
Good question, I have never liked this either.
Basically what the USB committee has specified are virtual
channels (they call them endpoints, since this is a point
to point connection).
One USB connection is shared between multiple virtual
channels each being able to receive or transmit only
(except the control endpoint - bizarre ;*) Plus there
is one control channel.
Basically this allows in one device for multiple data
streams with out additional logic (well thats of course
a lie as well ;*). A good example is a USB Video Phone:
- one endpoint for video
- one for audio input
- one for audio output
- plus of course the control endpoint which gives you a
GPIO port of up to 1M bits (keypad)
Of course the above could be multiplexed but for some
obscure reason thats how the USB guy did it.
I personally have never used more than one in and one out
endpoint, besides the control endpoint, but had to pay the
price and implement all the overhead ...
> *What 1/2/3 in the UTMI Level1/2/3 specs.It is not mentioned anywhere
> in the UTMI spec.
> *Any calculation formulas that help determine my fifo sizes.I am
> aiming basically at a maximum ISO tranfer case.
Hmm, read latency vs. write speed ?
Think about it ... it's simple ...
> *Which UTMI interface do i choose ? (16 bit/8 bit)
Chose a PHY first then the interface. I believe 8 bit
bi-dir is most common ...
> Awaiting your answers
> Thanks
> Rajesh
rudi
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