Mailing Lists: Apple Mailing Lists
Image of Mac OS face in stamp
 
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Continous isochronous transfer, high bandwidth transactions

At 12:29 AM +1100 2/15/05, John Dalgliesh wrote:

> Also, in high speed mode, how does one account for more than one 
 transaction in a single microframe?  Should the framelist simply
 contain a frReqCount that is >1023?


Hmmm, not sure about the terminology there, but I believe the framelist in
high speed mode describes microframes, or whatever you call the thing that
there are 8 of in the old 1ms frame. So each one is no more than 1024
bytes. Not quite sure how that affects the 'start frame' numbering 'tho.


I think you almost nailed this. I covered this in my WWDC 2003 presentation.

Swap frames for micro-frames and you've more or less covered the difference between full speed and high speed. The exception is that start frame is still a frame. A high speed Isoc transfer can not start on arbitrary micro-frame, but must start on a frame boundary.

The other difference is that "packets" can be larger, they can now span 3 packets. The USB spec specifies how endpoints larger than 1024 bytes behave, with a set pattern of up to 3 packets. These packets behave exactly like a packet of larger than 1024 bytes to software.

The only wrinkle to this is that there was some confusion as to how to specify these larger endpoint sizes. The sizes can be 0-3072, the endpoint size is specified as (1,2,3)*(0-1024), and I've forgotten which one we use, and we used a the other one in the very first implementation. (I think we should be using 0-3072, I'll have to check.)
--
Barry Twycross
email@hidden
---
USB, it's not a Dyslexic BUS. (Thanks to TC.)
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Usb mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
http://lists.apple.com/mailman/options/usb/email@hidden

This email sent to email@hidden
References: 
 >Continous isochronous transfer, high bandwidth transactions (From: Juan Pablo Pertierra <email@hidden>)
 >Re: Continous isochronous transfer, high bandwidth transactions (From: John Dalgliesh <email@hidden>)



Visit the Apple Store online or at retail locations.
1-800-MY-APPLE

Contact Apple | Terms of Use | Privacy Policy

Copyright © 2007 Apple Inc. All rights reserved.