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Message
From: Rudolf Usselmann<rudi@a...>
Date: Mon Feb 16 09:35:09 CET 2004
Subject: [usb] control transfers
On Mon, 2004-02-16 at 14:21, i_rajesh1@r... wrote:
> Hi all,
> Can anyone help me with how the calcultions in Table 5-2 on page 42 of
> USB2.0 spec are done.Awaiting your response
> Thanks
> Rajesh
Ahh, you finally found the bandwidth tables !!! ;*)
Lets see:
Max Bandwidth = (45 bytes protocol over head +
Bytes/frame useful data +
Bytes Remaining) * Max Transfers
Basically you calculate the maximum possible data amount
you cant transfer for a certain packet size (Data Payload).
The protocol overhead is fixed, depending on the Payload
Size, you can transfer a certain number of packets in one
frame (Max Transfers). The remaining bytes is the wasted
bandwidth due to Frame utilization. As you can see the
larger the packet the better is the utilization. However
if you have to resend one of the large packets due to some
transfer errors, your utilization drops dramatically. So
you need to find the best solution for your application.
Fo video applications, I would suspect isochronous endpoints
would be more appropriate, and you should look at the tables
on pages 45 and 46.
Regards,
rudi
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