interference between scc serial and ethernet: more informatio n

[Brown, David (dbrown03)]

Problem found!
Thank you for the comments and suggestions.

The board supports multiple levels of output (RS-232, RS-422, etc) on the
SCC ports, controlled by Port B pins.  I had initialized the pbpar/pbdir
backwards for these pins.


> -----Original Message-----
> From: Brown, David (dbrown03) [mailto:DBrown03 at harris.com]
> Sent: Friday, May 05, 2000 10:17 AM
> To: linuxppc-embedded at lists.linuxppc.org
> Subject: interference between scc serial and ethernet: more
> information
>
>
>
> The target is a custom board similar to the EST8XX
> configuration, with an
> 860 and an LXT908 PHY.  I ultimately need to run PPP on SCC3.
>  When ethernet
> receives data, it messes up SCC3's configuration somehow.  I
> briefly tested
> with SCC2 and saw the same thing, but I have concentrated on SCC3.
>
> It's a 50MHz MPC860, identified by 8xxrom as XPC860xxZPnnC1
> and actually
> stamped as XPC860ENCZP50C1.  Running at 50MHz.
>
> Three nodes on the ethernet: the target, the Abatron BDI2000, and the
> development host.
>
> Case 1) Linux boots with default parameters, no IP address.
> I use SCC3
> serial, no problem.  Then, on the development host, I ping a
> non-existent
> address (causing an ARP request broadcast).  After that, the
> SCC3 serial is
> not working.  Sometimes, when I write to SCC3, garbled
> characters come out
> (like it's the wrong baud rate).  Other times, nothing comes
> out at all.
>
> Case 2) Linux boots with IP address parameters.  I use SCC3 serial, no
> problem.  Then, on the target, I ping a non-existent address.
>  Serial still
> works fine.  I get "neighbour table overflow" messages.
>
> Case 3) In enet.c, in cpm_enet_rx(), I commented out code so that all
> received frames get tossed.  Again, SCC3 serial stops working when the
> development host pings an unknown address.
>
> I tried activating kgdb to debug this, but kgdb stops working
> as soon as the
> init shell starts.  It seems to be a fight over which process
> gets the input
> data.  I'm looking at it with BDM, but that's quite slow
> since I have to
> translate memory references.
>
> I see four potential possibilities.
> a) A bug in the enet or serial driver.  Not likely, since
> others report that
> Ethernet and SCC serial ports work simultaneously for them.
> b) A hardware problem on my board.  My co-worker says that's
> unlikely, since
> his low-level test software exercises Ethernet RX and uses SCC3 as the
> console.
> c) A blatant configuration error in my setup of Linux.  Not
> likely, since
> Ethernet and Serial each work independently.
> d) My board violates some assumptions made by Linux and/or
> the drivers.
> That seems to me to be the most probable, but I can't think
> of what it might
> be.
>
> Please feel free to throw out random ideas as to what I
> should look for.
>

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