Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Re: [802.3ae] RE: Clause 45: MDIO Electrical Specifications


The PICS should be viewed as a 'tick box' list of conformance rather than a set of
conformance tests.  They are not intended to give much detail, instead they reference
out to the main text of the standard where the details are located. However, the points
you raise are still valid since they highlight some shortfalls in the spec.

One by one :
EC8 IOL : Sounds OK to me, I'll use my editor's licence to raise a comment for this
round to add this requirement to table 45-62.
EC8 IOH : Again, this sounds OK and I'll raise a comment to add this to table 45-62.
For the open drain driver case, this measurement is not applicable.
EC6 Bus loading : You are correct.  This is not a component level specification but is
a system level specification for the capacitance of all the devices and PCB routing
combined together.
EC5 Input capacitance : I agree that 10pF may be challenging, but the vallue was agreed
by the committee and at the time no objections were raised.  Keeping this value as low
as possible is important since it allows as many devices as possible to share the bus.
However, if you feel that this number is too low then please submit a comment at
sponsor ballot with an alternative value and some supporting data to justify the


Tord Haulin wrote:

>  Edward Turner:
> I have a few questions concerning the MDIO Electrical Specifications.
> The table in the PICS proforma section isn't all that explicit
> on measurement conditions. As long as the measurements are taken by
> humans we can quite easily understand the underlying meaning of the
> specifications and overlook inconsistent current direction
> specifications and trouble with inequalities and mins and maxes for
> negative numbers etc., but there are a few aspects beyond that which are
> trickier.
> Spec points:
> The best guess for a voltage to use for this measurement would be the
> highest allowed VOL voltage 0.3V (EC2)
> For push pull drivers, the corresponding choice for an IOH measurement
> voltage would be the lowest allowed VOH voltage 1.0V (EC1)
> For the option with open drain drivers and a resistive pull-up however
> the same test condition would dictate a resistance that would overload a
> driver trying to pull it low.
> EC6 Bus Loading
> interoperability but for ensuring a performance level of a collection of
> units with MDIO interfaces joined with some network. Therefore I assume
> it is not mandatory or even applicable to components.
> EC5 Input capacitance for MDIO
> The 10pF limit can be difficult to support both for MDC and for the MDIO
> wire of MDIO in particular, given the wide variety the wide variety of
> mechanical design and subassemblies possible, sometimes with several
> devices connected to MDIO.
>  I would appreciate some comments and guidance on how to interpret the
> specifications.
> Best regards Tord Haulin
>         -----Original Message-----
>         From: Edward Turner
>         Sent: Thu 3/1/2001 4:23 PM
>         To: stds-802-3-hssg@xxxxxxxx
>         Cc:
>         Subject: Re: Clause 45: MDIO Electrical Specifications
>         Jeff,
>         As you correctly point out, the conclusion of the MDIO
> Electrical ad-hoc was to
>         recommend to IEEE P802.3ae that JEDEC JESD8-11 be adopted as the
> MDIO electrical
>         interface. This is what I reported at the opening IEEE P802.3ae
> Task Force
>         meeting in January and, as you point out, is recorded in the
> meeting minutes in
>         the General Presentations section
>         ( -
> pages 15/16).
>         Please note however that this was a report of the recommendation
> of the Ad-Hoc
>         given at the start of the meeting. When the Clause 45 track met
> later in the
>         week to resolve comments, the track discussed the ad-hoc's
> recommendation in
>         relation to D2.0 comment #1115 and the conclusion of this
> discussion was a
>         decision to use electricals based on JEDEC JESD8-11. These
> electricals are a
>         1.2v instance of JEDEC JESD8-11 with some additional parameters.
> This is
>         documented in the comment resolution database against comment
> #1115
>         ( -
> Page 76) and was
>         also reported by Ben Brown in his Logic Track report at the
> close of the IEEE
>         P802.3ae Task Force meeting
>         ( -
> Page 5).
>         In conclusion, while the ad-hoc made a recommendation, during
> comment resolution
>         this recommendation was modified and I am bound by the results
> on the comment
>         resolution process, which were approved by the Task Force, when
> preparing the
>         draft. You are therefore correct in saying that the changes that
> I made to the
>         draft do not match the report I gave of the Ad-hoc's
> recommendation at the start
>         of the meeting. This however is all part of the comment
> resolution process. Note
>         however, this is not to say that the work of the Ad-Hoc was
> ignored, it is the
>         basis of what appears in the draft today.
>         In relation to your new comment, I feel I have to put a
> 'proposed reject'
>         against it, citing comment #1115 from D2.0 - please don't take
> the reject
>         personally! I feel I have to do this as I believe that the
> current draft is
>         aligned to the consensus of the group. However, as with all
> comments, the actual
>         response will be discussed and decided at the upcoming meeting,
> in this case
>         during the Clause 45 track.
>         I do believe that the selection of a electrical specification
> for Clause 45 is a
>         most difficult task in particular in relation to selecting an
> approach that is
>         acceptable today, but will not become a burden to future
> implementations. I want
>         to thank you, and everybody else that has taken part in this,
> for the
>         contributions so far. As you will no doubt have noted there was
> another
>         suggestion for the Clause 45 electrical interface yesterday and
> I hope that now
>         there is wider interest we can all work together to come to a
> acceptable
>         consensus.
>         Respectfully,
>         Ed
>         "Jeff Porter (rgbn10)" <j.porter@xxxxxxxxxxxx> on 01/03/2001
> 03:55:27
>         Sent by:  "Jeff Porter (rgbn10)" <j.porter@xxxxxxxxxxxx>
>         To:   Edward Turner/GB/3Com@3Com
>         cc:   stds-802-3-hssg@xxxxxxxx
>         Subject:  Re: Clause 45: MDIO Electrical Specifications
>         Ed,
>         I submitted a comment to D2.1 on this issue, included again at
> the bottom
>         of this note.  The comment is that D2.1 does not reflect the ad
> hoc
>         decision that was reported in Irvine, namely to adopt JEDEC
> JESD8-11
>         for MDC/MDIO. The suggested remedy is that we simply reference
>         JESD8-11 (, "Free Standards") as the MDIO
> interface.
>         For D2.2 (Friday?) and D3.0 (March meeting) I suggest leaving
> text as is,
>         "complete" in some sense, or accepting my comment and resetting
> to the
>         ad hoc recommendation and referencing JESD8-11 directly.
> Additional
>         tweaks can wait for D3.0 comments.
>         FYI, my recollection of why JESD8-11 is proposed:
>         -- In earlier meetings, the consensus was that the Clause 22
> electrical
>            interface was no longer practical (voltages too high).
>         -- In earlier meetings, the consensus was that 10G did not want
> to
>            spend energy defining new "logic families", that is,
> non-standard
>            interfaces, for XGMII and MDIO, since there seem to be plenty
> of
>            digital interface standards to reference. (We seem to be
> spending
>            energy now). An ad hoc was formed to report a recommendation
> at Irvine.
>         -- Many comments were made that the new interface should last
> for
>            many years, not just a solution for 10G only. (since MDIO
>            may need to connect to phy's of different generations.
> Changing
>            addressing and electrical now, but not again for a long while
> since three generations of MDIO in one box is unthinkable.)
>         -- HSTL was repeatedly adopted/affirmed for XGMII interface.  As
> a practical
>            matter, systems with XGMII interface will have a 1.5V supply
> available.
>            No other P802.3ae interfaces infer a supply voltage.
>            (OK, as a practical, practical matter, it seems that at least
> for 0.18um
>            parts, the "HSTL" XGMII interface can be designed to be
> powered at
>            either 1.5 or 1.8V, even though standard only says 1.5V.  In
> non-standard
>            systems using 1.8V "HSTL", perhaps only 1.8V supply would be
> available,
>            but then I would expect those systems to design MDIO to
> operate at
>            either 1.5 or 1.8V, also outside standard.)
>         -- JESD8-11 provides two approaches for future proofing:
>            ** If P802.3ae says nothing about "Normal Range" (Vdd 1.5+/-
> 0.1V)
>               versus "Wide Range" (Vdd 0.9-1.6V), then every Clause 45
>               must support operation at interface Vdd=1.5V, insuring
> compatibility.
>               Part vendors could choose to support wide range, and
> system
>               implementers could select wide range parts, and operate
> the interface
>               on any supply between 0.9 and 1.6V.
>            ** If P802.3ae requires, in addition to JESD8-11,
> specifically
>              "Wide Range" support, then compatibility is also assured,
> since every
>               Clause 45 MDIO interface would operate with an interface
> supply between
>               0.9 and 1.6V. (i.e. 1.5V+/-0.1V, down to 1.0V+/-0.1V).
>         -- XGMII spec came from JEDEC (JESD8-6), JESD8-11 was available
> and seemed to
>         meet
>            the consensus goals, it was proposed in ad hoc, and despite
> prodding from Ed,
>         no
>            alternatives were proposed, recommendation (by default) was
> reported
>            at Irvine.
>         From (unapproved) Irvine minutes, I only find:
>         "Mr. Turner gave a quick ad-hoc MDIO report. A number of
> individuals from both
>         the
>         802.3ae and 802.3af committees worked on the new electrical
> interface
>         specification and
>         they selected an interface with an expected long life. This
> interface will be
>         compatible
>         with lower voltage devices that emerge in the future. They
> recommended the JEDEC
>         standard JESD8-11 interface. The ad-hoc work is
> finished, Ed
>         proposed
>         these ad-hoc conclusions be added to the next version of the
> draft standard."
>         Do I think JESD8-11 is perfect "as is"?  No - while Normal Range
> requires >2mA drive, Wide Range only requires an anemic 100uA (as does
> table in
>         D2.1).
>         Though 2.5MHz is slow, perhaps we should still say something
> about expected
>         loading,
>         desired range of edge rates, etc.  But I'm confident part
> vendors would make
>         good
>         guesses here.  For the standard, I'm just suggesting that we
> start back at
>         JESD8-11, and make any *needed* refinements as D3.0 comments.
>         Thanks,
>         Jeff
>         Edward Turner wrote:
>         >
>         > Rick,
>         >
>         > I support your effort to bring forward these potential issues
> to the group at
>         > large.  I also encourage further reflector discussion if
> people feel there is
>         > something broken in the draft.  It is important that we make
> the correct
>         > decisions when these items come up for vote at the meeting.
>         > I was not sure if you were at the meeting and wanted to
> explain some of the
>         > background thinking that had gone on 'off the reflector'
> during the ad-hoc and
>         > at the Irvine meeting.
>         > I also encourage any of you who are attending the meeting and
> have points to
>         > raise on the MDIO electrical interface to come along to the
> Clause 45 sub
>         track
>         > so that we can hear your concerns when we discuss the
> electrical interface
>         > comments.
>         >
>         > Regards
>         > Ed
>         >
>         Clause: 45
>         Subclause:
>         Page: 45.222
>         Line: 15
>         CommentType: DISAPPROVE (Technical)
>         Comment:
>         Resolution of Draft 2.0 Comment 1115 ""adopt[ed] an instance of
> the
>         JESD8-11 standard with a VDD of 1.2V""  JESD8-11 (,
> ""Free
>         Standards"") was selected by an apathetic ad-hoc.
>         However, JESD8-11 does not support 1.2v only operation.  The
> choices,
>         Normal and Wide range, are mentioned in the title of JESD8-11
>         2.2.1 Normal Range (1.4 to 1.6V Vdd)
>         2.2.2 Wide Range (0.9 to 1.6V Vdd)
>         In either case, the sending and receiving Vdd for this interface
> must
>         track within 0.1V (Note 1 in 2.3.1 and 2.3.2)
>         An MDC/MDIO implmenter could select to support either Normal or
> Wide
>         range since interoprability at 1.5V is maintained.  If all
> connected
>         parts in a system are wide range, a supply lower than 1.5V
> nominal
>         could be used.
>         When an XGMII (HSTL JESD8-6) is present, 1.5V will be available.
> CommentEnd:
>         SuggestedRemedy:
>         Change 45.4.1 to read
>         ""The electrical characteristics of the MDIO interface are
> defined
>         in JESD8-11.  Pin input capacitance is limited to 10pF
> maximum.""
>         Retain NOTE, change to read ...""Vdd of 1.5V""
>         Delete Table 45-41.
>         Annex 45A, change 1.2V Vdd to 1.5V Vdd throughout.
>         RemedyEnd:
>   ------------------------------------------------------------------------
>                   Name: winmail.dat
>    winmail.dat    Type: DAT File (application/x-unknown-content-type-dat_auto_file)
>               Encoding: base64