[indy99]

 Due to Nekochan's demise, there appears to no longer be any info related to altering the CPU speed settings on the SGI Fuel platform to prepare for PIMM replacement (upgrade or downgrade).  I know some of the old-timers will know how to do this.

Can someone please publish the technique to perform this.  I know it has to do with setting speed and timings in the L1...but no idea what commands to use.

Don't believe it's possible to do this via the L1.  The methods I've successfully used are via POD mode in the PROM, and by using the IRIX flash command.  Between those IRIX flash is the relatively safest method, mostly because it has some publicly available documentation.

flash(1m)   


-f   Specify different (than currently in PROM) configurations
  values to be used when the new images are flashed.  These
  values include the speed of the CPU, hub, and size of the
  cache.  This option should be used with great care as cause
  the machine to freeze and be rendered unusable if incorrect
  values are given.

Make the changes with the currently clocked cpu in place, shut down and install the new PIMM.  The system will reboot expecting to find a CPU with *exactly* the values you specified, so a simple syntax error can be fatal.  Make sure you have all of the required parameters for the incoming PIMM ready to insert before you attempt the flash.

I've also did it once from POD mode, but it's been long enough ago I won't trust my memory to lead you into a non-recoverable dead end.  

Either was you go you should be prepared for at least a semi-white knuckled experience.  If it goes south I don't know of publicly discussed method of recovery.

As far as downclocking goes I have zero experience, but I'm pretty sure someone on nekochan crashed and burned trying it. On the other hand as long as the new (faster) PIMM is capable of running at the slower values in the PROM you might be ok. A number of people posted on nekochan asking why their newly installed 600mHz PIMM still showed up as a 500mHz in an hinv, and were able to successfully flash the new values post install.  So going from slower to faster might be recoverable after the fact.