On 23 Dec 1997, Craig Dewick wrote:

> Has anyone ever succeeded in modifying their 3/80 so they can fit a faster
> (say 33 MHz) CPU and co-processor? I have a couple of pairs of 33 MHz
> 68030/68882's which I'd like to experiment with in a 3/80, but I don't know
> if it's worthwhile trying to work out how to adjust the timing circuitry to
> boost the CPU clock speed.

The CPU clock is generated by a 40 MHz crystal on the motherboard.  The
signal is split into two paths.  The frequency of one path is divided by
two, while the other is left alone.  These two paths then meet up at a
jumper on the board, close to the CPU.  (It's labeled '20 40'.)  The 3/80
ships with a shorting block (jumper) on the 20 MHz side, but you can
easily move it to the 40MHz side.  (I have measured the 40 side with an
oscilliscope and it is indeed 40 MHz, if you're worried.)

If you do move the jumper, you will need to find a 40MHz 68030 and 68881. 
I don't know how rare these are, or if they even exist.  If you'd like to
run a 33MHz '030, you should probably replace the 40MHz crystal on the
motherboard with one that runs at 66.  I can't imagine that there would be
anything else you need to change.

If you DO speed up the clock, make sure that you change the delay speed in
arch/sun3x/sun3x/idprom.c and recompile a new kernel FIRST.  Right now,
the sun3x port of NetBSD doesn't actually measure the clock speed - it
just guesses based on the machine model. 

-J