Re: [usb] usb bandwith

["Vikas T Rao " <vikasraot@myw.ltindia.com>]

** Proprietary **

hi,

if we have to have the bandwidth same as the data transfer rate, then we have to send data only continuously without any additional information. this means we should not send any header/footer(PID, ADDR, CRC, HS etc) along with the data. this is contradictory to the USB spec and hence there can't be any application which will utilize 100% bandwidth.

as mentioned in the spec, the maximum amount of data that can be transferred in a micro-frame is limited because there can't be any possibility of sending more than those many number of packets. this is because no single packet can be sent in two micro-frames. remember that the maximum packet length for any endpoint can't be varied. so for every micro-frame some amount of bus time will be idle. thus the bandwidth is not fully utilized by an endpoint. even though the host tries to send/receive the packets continuously for 'n' number of endpoints in a single micro-frame, it can't utilize 100% bandwidth based on the reason mentioned in the above paragraph.

regards,
vikas.

>>> meizx@ict.ac.cn 08/13/02 07:25AM >>>
hi,all
  please help me to verify the three usb transfer rate 480Mb/s,12Mb/s,and 1.5Mb/s defined by usb specification.in full speed mode,one endpoint in isochronous mode can transfer 1023 bytes/ms---8Kbits/ms,8Mbits/s.that's to say,12Mb/s bandwith cannot be used up in full speed mode.is there any application that use alll the 12M bandwith? 
  in high speed mode,considered the isochronous transfer,one frame includes 8 microframe.given three transactions can be transfered in each microframe,usb can deal with 24Mbytes/s,while half of its bandwith are useless.i cannot understand.

regards
              MeiZX
              meizx@ict.ac.cn 
                 2002-08-13
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