[802.3ae] RE: Clause 45: MDIO Electrical Specifications
Edward Turner:
I have a few questions concerning the MDIO Electrical Specifications.
The table 45.5.5.14 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:
EC8 IOL
The best guess for a voltage to use for this measurement would be the
highest allowed VOL voltage 0.3V (EC2)
EC7 IOH
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@ieee.org
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
( http://www.ieee802.org/3/ae/public/jan01/minutes_0101.pdf -
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
( http://www.ieee802.org/3/ae/comments/d2.0/D2-0-Comments.pdf -
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
( http://www.ieee802.org/3/ae/public/jan01/brown_1_0101.pdf -
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@motorola.com> on 01/03/2001
03:55:27
Sent by: "Jeff Porter (rgbn10)" <j.porter@motorola.com>
To: Edward Turner/GB/3Com@3Com
cc: stds-802-3-hssg@ieee.org
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 (www.jedec.org, "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
MDIO
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. www.jedec.org 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: 45.45.4.1
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 (www.jedec.org,
""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:
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