arnyk wrote: > I find the third paragraph hard to follow. > > "This packet noise consists of two parts: noise from the USB protocol > engine and from the USB PHY. The protocol engine noise does not depend > on the input signal quality, just the data, so its impact is always > going to be the same no matter what is done with the input. The PHY is > the part that actually connects to the electrical signals on the bus, > ITS contribution to packet noise IS dependent on the quality of the > input signal. This is the part the REGEN targets." > > It does not seem to directly comment on 8 KHz noise, except perhaps very > obliquely. But the oblique explanation seems to contradict claims made > on the site's home page. How are we to know which part of the web site > is more important? > > Since you seem to understand it please explain, if possible with quotes.
I'm pretty sure you are feigning not understanding this as another one of your forum debate tactics but : *"This packet noise consists of two parts: noise from the USB protocol engine and from the USB PHY.*" You already posted & quoted a link which explains exactly what this means http://forums.slimdevices.com/showthread.php?103684-uptone-audio-regen&p=819082&viewfull=1#post819082 > > > The 1 ms frame rate in full speed / low speed USB, is used for a number > of purposes, such as scheduling access to the bus, and as a timing > reference for interrupt and isochronous transfers. > > For high speed, a higher frame rate was deemed appropriate, while still > maintaining a relationship with the existing 1 kHz rate. > > To this end, high speed uses the 'Microframe' which is 125us long (8 > Microframes per millisecond). The correspondence with the 1ms frame > numbering is maintained in the high speed SOF packets by repeating each > frame number in 8 successive Microframes. So, can I ask why you post & quote links which you now claim not to understand the meaning of? \"THE PHY IS THE PART THAT ACTUALLY CONNECTS TO THE ELECTRICAL SIGNALS ON THE BUS, ITS CONTRIBUTION TO PACKET NOISE IS DEPENDENT ON THE QUALITY OF THE INPUT SIGNAL. THIS IS THE PART THE REGEN TARGETS.\" I'm not John Swenson but I have read what he says & my understanding of this is that the USB PHY has to work harder to recover clock & data from signals that have some degradation in them. In other words the lower the signal integrity the harder the PHY has to work to do this recovery. If you need a more technical explanation look here http://electronicdesign.com/boards/480-mbitss-signal-integrity-becomes-issue-usb-20-designs > The IEEE-1394 specification requires two differential pairs, which > simplifies the task of recovering clock and data signals. These signals > can be extracted by simply implementing a logic function on both pairs. > USB 1.0 and 2.0 specifications require only one differential pair. This > makes it more difficult to recover the clock and data signals. With USB > 1.0 at 12 Mbits/s, one could perform a brute-force oversampling of data > using a 48-MHz clock to extract the data. But at the USB 2.0 rate of 480 > Mbits/s, this approach would require a 1.6-GHz clock. Because sampling > at these speeds isn't practical, it's necessary to use a more > sophisticated clock/data recovery method. > > With the single differential pair that's used for USB 2.0, the ability > to read at the middle of the data eye is critical. One method for > performing clock and data recovery is to use a delay-locked loop (DLL) > to generate a number of sampling clocks. With this approach, the > designer must incrementally select a different tap until it's at the > middle of the data eye. > > A 480-MHz clock cycle is 800 ps long. By sampling data every 80 ps for a > few clock periods, it's possible to compare the data recovered from each > tap and "vote" on the results. Over several clock cycles, it's possible > to determine the best sample point—that is, the center of the data eye. ------------------------------------------------------------------------ jkeny's Profile: http://forums.slimdevices.com/member.php?userid=35192 View this thread: http://forums.slimdevices.com/showthread.php?t=103684
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