Lpc2000

Can someone point me to a definitive / application reference for the Watchdog
circuit used in the LPC2xxx - )one that is better than the user manual for
LPC2292)

I recently started trying to use the watchdog in the LPC2292.
Knowing no better, I decided to feed the watchdog once every time
I went round my event loop. I was careful to disable* interrupts before
writing 0xAA and 0x55 to WDFEED, and then re-enable the interrupts
afterwards. But I could not get the watchdog to behave - it would cause
interrupts no matter what (long) duration I set for the period (for
debugging I did not enable the reset, and I placed a
breakpoint in a Watchdog interrupt routine).
Typical periods I tried were around 1 to 10 seconds, with the PCLK at
60 MHz.

*using the macros provided in Crossworks. Note also that my spurious
interrupt routine merely writes to VICVectAddr and returns.

But if I placed a breakpoint in my event loop, and (from the debugger)
said "continue" before the watchdog timed out, the watchdog would not
interrupt.

My main event loop is pretty tight - it mostly looks to see if data have
arrived in buffers (put there by peripheral interrupt-service-routines).
Only when enough data are available will time-consuming calculations
be performed.

Seeing that the system did work if I placed a manual delay between
watchdog feeds, I tried only feeding the watchdog once every keyboard
scan (polled from a timer flag in the event loop, no faster than once
every ten milliseconds). This seemed to work fine, and continues to
work now I have enabled the watchdog reset.
And the watchdog does cause a reset if I deliberately enter an endless
loop.

Does this fit with the experience of others?
What constitutes over-feeding of the watchdog? Is it documented anywhere?
(It is possible that I do not understand what is going on).
I invite comments.

Regards,
Danish