[Avila] IXP4xx watchdog reset hang

[Ron Eisworth]

David,
The Avila board has an optional "hardware" watchdog which may be of some use
to you. This watchdog uses the watchdog timer built into the Maxim/Dallas
DS1819 reset generator. This hardware watchdog will generate a full RST to
the board and also resets the onboard Flash (same as push button reset). To
enable this function, make sure resistor R11 on you board is populated. This
resistor is located on the solderside of the board by the CompactFlash
connector. If it isn't populated, load it with a zero ohm resistor (if you
don't have a zero ohm resistor you can just short across the pads with some
solder). Your software then must provide a strobe pulse to GPIO14 of the IXP
processor once every 1.12 seconds.

Hope this helps,

Ron

-----Original Message-----
From: David Holmer [mailto:dholmer at jhu.edu]
Sent: Wednesday, March 08, 2006 7:10 AM
To: avila at lists.unixstudios.net
Cc: dholmer at cs.jhu.edu
Subject: [Avila] IXP4xx watchdog reset hang
Subject: [Avila] I've been working on getting the IXP4xx built in watchdog time operational
on our Avila boards. I've had partial success using the driver that comes in
the 2.6 kernel with the 0.6 release. The problem is that although the kernel
driver seems to setup the watchdog correctly, and the watchdog triggers a
reset at the right time (when it stops getting updates), the Avila board
only seems to reboot successfully some of the time. Often the board will
hang after the watchdog reset and I see no output on the serial port (i.e.
Redboot isn't coming up). Sometimes the watchdog works perfectly and the
system reboots normally.

I did more investigation into the topic and I suspect I found the culprit.
It seems that the IXP4xx watchdog only triggers a local cpu-reset. The issue
seems to be if the flash isn't in read mode (e.g. write or erase modes) when
the watchdog triggers, then the cpu can't load the bootloader out of the
flash. Since we're using a JFFS2 file system, the flash could be in these
other states at any time.

I found an Intel Application Note that seemed to have useful information:
"Intel StrataFlashR Memory to IntelR IXP42x Product Line of Network
Processors and IXC1100 Control Plane Processor Design Guide, Application
Note 785" at http://download.intel.com/design/flcomp/applnots/25378604.pdf
In section 4.5 "Reset Consideration" this app note seems to describe the
issues I'm experiencing and says that when interfacing StrataFlash with an
IXP42x the  PLL_LOCK pin on the IXP42x should by tied with some pulse width
extension circuitry to the RP# pin on the StrataFlash.

Do the Avila boards have this reset connection that Intel describes in the
App Note? If not is this something that is difficult to add to the PCB? Are
other people using the watchdog and experiencing this issue as well?

- David Holmer

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