OPENCORES.ORG

-----Original Message-----

You don't transfer the 27MHz clock over USB for any speed, you synchronize
the two clocks using the USB.

See section 5.12, Special Considerations for Isochronous Transfers, in the
USB 2.0 spec.

Marc Reinig
System Solutions

> -----Original Message-----
> From: usb-bounces@o... [mailto:usb-bounces@o...]On
> Behalf Of i_rajesh1@r...
> Sent: Wednesday, February 11, 2004 3:08 AM
> To: rudi@a...; usb@o...
> Subject: [usb] USB bw related calculations
>
>
> Hi Rudi,
> Thanks for the help regarding the Endpoints question.
> There was one more question.
>
> What does 1/2/3 in the UTMI 1/2/3 spec concern about.Can you help me
> out on what these numbers mean.
>
> And regarding the Bandwidth calculations i have come up with a
> summary(after referring a few docs).I have made it short and sweet.We
> are in the spec phase of the project and need to decide on HS/FS.Can
> you please have a look at it and point out any errors(if any :-)).This
> doc may also be of help to others who need to decide on many things
> during the spec phase.
>
> Thanks
> Rajesh
>
>
>
> +-------------+
> BW calculations
> +-------------+
>
> Choice of operation speed : (HS/FS/LS)
>
> Max BW  in each case
> --------------------
>
> One requirement is that transactions on the bus are
> always framed into 1ms quanta. This analysis model focuses
> on the number of  byte transfers per frame (BTF) ,
> e.g. it looks at the opportunities to transmit bytes in
> a 1ms time period even though the bus is a bit serial bus.
>
> ------------------------------------------------
> Mode   	MaxBW   BTF 	Utilizable  %Util(max)
> ------------------------------------------------
> HS 	 480 	60000	1024*3*8        41
> FS 	 12   	1500 	1023		68
> ------------------------------------------------
>
> Considering the HS case 480Mbps translates to
> 480M/(8*1000) = 60000 BTF.
>
> USB bandwidth is divided into 1,000 frames per second.
> Isochronous transfers in USB 1.1 were limited to a single
> packet per device endpoint per frame. The largest packet
> was 1,023 bytes, yielding an aggregate data transfer rate
> of 1Mbyte/sec.
>
> USB 2.0 not only increased the data rate to
> 480Mbits/sec., it also subdivided each of the frames into
> 8 microframes to reduce the need for buffering in the device.
> USB 2.0 also increased the number of 1,024 byte packets
> per microframe to 3 for each device.
> Thus, the achievable iso data rate in USB 2.0 jumps
> from 1Mbyte/sec. to 24Mbytes/sec. (1,000 frames/sec. x 8
> microframes/frame x 3 packets/microframe x 1,024 bytes/packet).
> { Valid for HS only }
>
> ?? While streaming out video one important consideration
> will be whether the video out is compressed or not.
>
> => Considering the compressed data transfer case 
> Normally Digital Video is compressed for transmission.
> Common standard is MPEG-2, designed for digital
> broadcast television level.
>
> Taking an example with the following requirement : 720x480 pixels per
> frame and 30 frames/sec,12 bits per pixel.
>
> BW = 720*480 pixels/frame * 30 frames/sec * 12 bits/pixel /
> {compression ratio }
>
> For a compression ratio=40 (max ?),
> required bandwidth is = 3.2 Mbits/s.
> (? Can be easily met by the FS port with lots of processing overhead)
>
> => Considering the raw data transfer case 
> The chip receives the analog signal from the camera and converts
> it to a digital signal formatted to either CCIR-601 or CCIR-656.
> The CCIR-601 formatting requires an 8-bit data bus and three
> additional signals. One of those signals is the 27-MHz video
> input pixel clock. The two remaining signals provide the
> horizontal and vertical timing for the 8-bit data bus. The
> CCIR-656 format is similar to the CCIR-601 format. There is an
> 8-bit data bus with a 27-MHz clock. However, the vertical and
> horizontal timing codes are embedded within the data stream.
>
> Reqd BW = 27 Mbits per sec.
> (?FS cannot handle this)
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