On Tue, 20 Mar 2001, John Maier wrote:

> I recently got the bug to hack on my /240.  There is not much technical data
> available on the DECstation hardware.

	I have no doubt.

> I have spent some time pouring over white papers on the R3000 and R4400
> chips and though I've learned much about the MIPS chips, I now have more
> questions than ever!!!
> 
> 1) On the /240 CPU daughter card, there are 3 major chips.
>     a) The heat sinked chip seems to be the R3000 CPU-FPU.

	Correct

>     b) What is the LSI L1A7242 and L1A7231?  LSI was recently bought by
> Philips and there is
>     little information on LSI chips.

	As per a recent email of the thread "No heatsinks on 5000/240
cpu?" those would be the CPU ASIC and the Motherboard ASIC. Definitely
custom jobs specifically for DEC, not likely you will find much doco on
either of those.

> 2) The R3000 is a time multiplex 32-bit bus chip, the PGA R4400 was packaged
> as 64bit bus, so is the bus going to the main board a 32 or 64bit path?

	Since the 5000/2x0 ran both R3x00 and R4x00, my guess is that it's
64 on the CPU card and possibly _to_ the motherboard ASIC, but no further
with the R4x00

> 4) There is no reference to 144pin PGA R3000 packaged CPU anywhere, anyone
> know exactly what make and model of R3000 DEC used?

	No clue, it was probably also a custom design just for DEC.

> 3) Does the SG-615P chip, on the daughter card, control the CPU frequency?
> If so, does it also generate the clock for the main board?

	No clue.

> Reverse engineering is a slow process and I've never seen a /260 so if
> anyone has schematics or other info they could copy and kick my way, I'd
> love it.  The last time I was in this mode, I put together a Z8000 board,
> but this is a bit more involved than that project and am still unsure of my
> future success...

	You might search the pmax mailing list for the thread "LSI
Logic" which had some past discussions on what a viable CPU replacement
would be, and perhaps some more tech info that would be useful. I would
also recomment searching for some keywords there, or going to
http://www.google.com/bsd

> My Goal?  To either make a replacement board or devise a method to upgrade
> an existing /2x0 to a bit more speedy technology.
> So far the IDT9R3081 (http://128.11.21.63/docs/79R3081_DS_3483.pdf) looks as
> if it may be a good CPU replacement with the help of a MQUAD/PLCC(84) to
> PGA(144) adaptor (most likely a custom job) This would allow the board to be
> ramped up to 50Mhz and get a bigger I/D cache.  However, the 50Mhz version
> is a 5.0V chip, so I don't know if this available to the board without a
> little wire hack :-)
> 
> As for the R4400 based /260, all I know is the R4600(133Mhz)chip is pin
> compatible with the R4400 but has some issue that can be address with some
> pin modifications per MIPS webpage

	There would also be some software issues in dealing with three (or
four?) different processor designs, but certainly not insurmountable (with
the proper know how)

> http://www.mips.com/Documentation/R4x00_common_design.pdf IDT make a R4400
> based chip that may be a candidate for a retrofit
> http://128.11.21.63/docs/79RC64474_DS_53993.pdf

	133MHz would certainly be a _little_ bit of a speed boost.

> I know this isn't really the forum for such a discussion, so if someone
> insists that I take this offline, no problem.

	Nonsense, this is probably the only forum, next to 
comp.unix.ultrix and the OpenBSD pmax mailing list. Good luck. I should be
able to grab the part number and revisions of the CPU if you need them
from a spare 240 Mobo I have at home.


	chris