Re: code-word alignment location
The proposed initialization sequence of Idles rudely interrupted by Packets
should be sufficient to initialize all PHY sublayers with no handshakes. CODEC
transparency and simple error control logic goes a long way towards simplifying
initialization procedures. Handshakes may be necessary when the link breaks or
does not come up properly. I'd at least like to start with this assumption
rather than assume that handshakes are required for initialization.
> Una Quinlan wrote:
> Thanks for the additional information here. One question I have regarding
> the non-packet codewords (excluding the 'Error' case which I have referred
> to in a separate email) is to do with PCS-level link initialisation and
> codeword usage for this.
> I am trying to think through the sequence of events to bring up a 10Gig link,
> comparing it with 1000BASE-X before. Moving up through the layers as far as
> the PCS:
> (1) PMD - If optics, need some form of 'Signal Detect', light power level.
> (2) PMA - Need clock-data recovery.
> (3) WIS (optional) - Need SONET (A1,A2) framing
> (4) PCS - need 64b/66b codeword alignment at a minimum.
> [ Aside: Does PCS codeword alignment belong in the PMA/WIS or the PCS? ].
> Codeword alignment might be difficult if there is no guarantee of an 'Idle'
> stream, or some special line startup code.
> A simple startup sequence would have the PCS transmit a ZZZZ/ZZZZ codeword
> repeatedly. And define a 7-bit type for Breaklink. Transmit this
> repeatedly until some handshake response comes - Breaklink Response.
> The Management Interface (not XGMII or XAUI) would be the source and monitor
> of link initialisation. The datapath to/from XGMII or XAUI would only be
> enabled once the link is up.
> Have you thought about a management interface for sourcing such codewords
> (i.e. a data source which is not coming from the MAC directly (but from the Serial
> Management interface)? Maybe Brad would add this extra interface on his
> drawing, and it would illustrate this.
> Providing a PCS Link Initialisation sequence will allow us to isolate faults
> on the external link from faults on the local XAUI links. I expect XAUI will
> also have some local link initialisation sequence, looking for Comma
> alignment, and Receive synchronisation. It would seem crazy to also require
> a Management interface to initialise this link, but there will probably need
> to be a minimal set of registers, for diagnostic purposes. However, with
> XGXS separated into two separate physical devices, would we need management
> registers on both sides?
> Una Quinlan
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