Recommendations for LXT971A PHY MII interrupt connection

Recommendations for LXT971A PHY MII interrupt connection

[Keith Outwater]

Greetings all -

I'm a hardware designer seeking to provide support on a custom MPC860T based
design for linux.
Does anyone have specific recommendations as to the best way to connect an
Ethernet PHY's MII
management I/F interrupt to the processor?  I'm using an Intel LXT971A PHY.

For example, are the general purpose external interrupts on IRQ[0:6] or the
CPM interrupts on port C preferred?
Is there a specific pin or interrupt that is preferred?

Thanks!

PS: (this is a bit off topic linux-wise, but related:  Wolfgang, what's the
preferred method as far a ppcboot is concerned?)


Keith Outwater
Sr. Electrical Engineer
Microvision, Inc.


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Re: Recommendations for LXT971A PHY MII interrupt connection

[Wolfgang Denk]

Hi Keith,

in message <E62DBC698514D511A1AC0003470C1314EE2BF3@exchange.mvis.com> you wrote:
>
> Does anyone have specific recommendations as to the best way to connect an
> Ethernet PHY's MII
> management I/F interrupt to the processor?  I'm using an Intel LXT971A PHY.

Ummm... what are your options? All designs look pretty similar to me,
the main difference being the interrupt pin they chose  for  the  PHY
interrupt, if any.

> For example, are the general purpose external interrupts on IRQ[0:6] or the
> CPM interrupts on port C preferred?

Softwarewise, it's easier to use one of the IRQ pins.

> Is there a specific pin or interrupt that is preferred?

No.

> PS: (this is a bit off topic linux-wise, but related:  Wolfgang, what's the
> preferred method as far a ppcboot is concerned?)

Being lazy, the preferred  (by  me)  method  is  not  to  use  a  PHY
interrupt  at  all  :-) You need the PHY interrupt only in cases when
you need to get informed about link status changes. Few  applications
really  need  this  type of information (although it's "interesting",
especially during board bring-up).

Hope this helps,

Wolfgang Denk

--
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd@denx.de
Bradley's Bromide: If computers get too  powerful,  we  can  organize
them into a committee - that will do them in.

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/

RE: Recommendations for LXT971A PHY MII interrupt connection

[Keith Outwater]

Thanks for the info Wolfgang!
As far as interrupt assignments go, the design is totally flexible as it
hasn't gone to fab yet.
Your statements below seem to imply that the Linux kernel doesn't' want or
need the MII interrupt. Is this correct?

 Keith

in message <E62DBC698514D511A1AC0003470C1314EE2BF3@exchange.mvis.com> you
wrote:
>
> Does anyone have specific recommendations as to the best way to connect an
> Ethernet PHY's MII
> management I/F interrupt to the processor?  I'm using an Intel LXT971A
PHY.

Ummm... what are your options? All designs look pretty similar to me,
the main difference being the interrupt pin they chose  for  the  PHY
interrupt, if any.

> For example, are the general purpose external interrupts on IRQ[0:6] or
the
> CPM interrupts on port C preferred?

Softwarewise, it's easier to use one of the IRQ pins.

> Is there a specific pin or interrupt that is preferred?

No.

> PS: (this is a bit off topic linux-wise, but related:  Wolfgang, what's
the
> preferred method as far a ppcboot is concerned?)

Being lazy, the preferred  (by  me)  method  is  not  to  use  a  PHY
interrupt  at  all  :-) You need the PHY interrupt only in cases when
you need to get informed about link status changes. Few  applications
really  need  this  type of information (although it's "interesting",
especially during board bring-up).

Hope this helps,

Wolfgang Denk

--
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd@denx.de
Bradley's Bromide: If computers get too  powerful,  we  can  organize
them into a committee - that will do them in.

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/

Re: Recommendations for LXT971A PHY MII interrupt connection

[David Ashley]

We had a problem where suddenly the ethernet would stop working, once
there was a lot of outgoing traffic from the box. It turned out it only
happened when plugging the ethernet into a full duplex switch instead of
a half duplex hub. In full duplex there are now two interrupt indicators,
on TX and RX. In half duplex the interrupt bits are shared. So the driver
has to know what duplex the PHY is in. How does it find out? The best way
is to allow the PHY to interrupt the cpu when the status changes.

The 10/100 rate seems irrelevant, the driver appears to get the information
then do nothing with it. But the duplex really matters.

I had the PHY interrupting on completion of the auto-negotiation. In that
case you don't get an interrupt if a line is unplugged, just when a line is
plugged in. The only problem seems to be what register to examine in the
PHY to find out the line status, there doesn't appear to be a standard.

An alternative is to program the PHY to only negotiate half duplex mode.
Then nothing really can change that you care about.

I think an important lesson here is do testing under various conditions. It
turned out in all our testing in the lab we had always plugged the box into
hubs, which were half duplex. It took some time for us to figure out why
the box was failing, first we were worried about the cabling, then the
switch itself, then the hardware on that box possibly being bad. It was only
after ruling all out that we figure out it was the full/half duplex.

We still haven't tried doing any testing with 10 base T though :^(.

-Dave

>Being lazy, the preferred (by me) method is not to use a PHY
>interrupt at all :-) You need the PHY interrupt only in cases when
>you need to get informed about link status changes. Few applications
>really need this type of information (although it's "interesting",
>especially during board bring-up).
>
>Hope this helps,
>
>Wolfgang Denk

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