[SI-LIST] Advantages of switching standards/BER/link recovery...
- From: "ruston, matt" <ruston_matt@xxxxxxx>
- To: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 19 Feb 2002 14:32:57 -0500
> All:
>
> Hi. A colleauge and myself are in the position of defending a particular
> bus standard that we chose to transfer data. I won't say what we selected
> (not yet - I will in a subsequent mail message), but here are some of the
> factors.
>
> - We need a respectable data transfer rate (>1.0 GB/s).
> - We have multiple boards with different power supply generation on each
> board.
> - We have 2 controlled differential impedance connectors to traverse (we
> can change them to single ended if need be).
> - We want to minimize the number of signals (and minimize ASIC/FPGA pins,
> board routing layers, etc.).
>
> We can do, say, 32 signals at 250 Mb/s each or 16 signals at 500 Mb/s
> each (both source synchronous). We can also do, say, 4 signals at 2.5 Gb/s
> each to give roughly the same bandwidth (8B/10B). The term "signal" is
> also being questioned. Do we need single ended or differential (management
> likes less lines)?
>
> As we are all aware, the faster we pump a bus, the higher BER we will
> get. Our question is: if you had to make this decision, which type of bus
> would you implement (2.5 Gb serial with a cumbersome link recovery
> protocol due to higher BER or go much wider and slow things down to an
> almost non-existent BER with no link recovery, or something in between)?
> Where is the line drawn on the speed scale that determines whether link
> recovery is necessary (assume an enterprise class system)?
>
> Also, would you prefer 16 differential signals at 500 Mb/s (32 lines) or
> 32 single ended signals at 250 Mb/s (32 lines)? Who has the better bit
> error rate and noise margin? Where do you think the industry is going
> (faster serial lines with link recovery such as IB or wider single ended
> standards such as IMB and Hublink)?
>
> I understand that I've left this rather vague (on purpose). I would
> appreciate general discussions on where you think things break (require
> link recovery), advantages of each type of bus, experiences, etc. Any and
> all thoughts are welcome.
>
> Regards,
>
> Matt
>
> Matt Ruston
> Signal Integrity Engineer
> Voice: 508-249-5223
> Fax: 508-497-8010
>
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