RM7900 datasheet boot-mode settings

[ruckusman]

Hi guys,

Long term project here to upgrade the SGI O2 with an RM7900 CPU - serious OCD...
For years, literally I couldn't find any datasheet on the RM7900, but recently lucked out and found the long form of the RM7965 datasheet here

https://www.datasheets360.com/pdf/-6475857418499999415
(part [subset] of the RM7900 family instruction manual)

My primary interest is in the boot-mode setting bit stream which begins on page 48 of the above document.

Now I believe that the boot-mode bit stream is also applicable to the RM7900 because, on page 48 - field (bit) 10 enables/disables the external cache.
The RM7965 doesn't have an L3 external cache controller, so to my mind that boot-mode bit stream setting is applicable to the RM7900.

Ideally I'd get my hands on this document, however it's nowhere to be found

For additional Detail Information regarding the operation of the PMC-Sierra see the latest PMC-Sierra datasheet for the RM79xx Family Microprocessors Data Sheet (doc. # PMC-2030581), Issue No. 11: September, 2006

Anyone have any thoughts on the matter?

I don't even have the CPU as yet, but need to sort this element out before attempting anything anyway...

[mattst88]

I have the same plans!

It's been a long time since I looked at any of this, but in 2018 I contacted Microsemi (which acquired PMC-Sierra) and asked for documentation no the RM7900, and they were unwilling to help. Their reply:

[ruckusman]

Hiya Matts88

I have fairly copious notes on various potential sources for the info - there were sources that sold dev kits Wind River systems is one such Org.

There are RM7900 spec sheets out there somewhere, but it's true internet quest territory finding one.

Are you on irixnet.org or forums.sgi.sh or their discord channel?
I haven't been on for a few months as I dosed the older laptop with a cup of coffee - the data (passwords) are intact just awaiting transfer - I am lazy -there was some interesting info re: RM7900 and the needed PROM mods AND apparently one of the guys on there knew an ex-SGI engineer that had the know-how to do the mods.

[mattst88]

I'm on irixnet.org, but not very active there. I don't believe I've ever created an account on forums.sgi.sh.

In terms of the PROM, I've disassembled it and found the code that checks the CPU type. Of course it doesn't know about RM7900 CPUs, so presumably it would fail there.

[ruckusman]

Hi Matts

I knew I recognised your handle from somewhere, I've read your blog about the chat with Jesse Barnes about this very possibility.

Have you acquired the 6.5.7 source with the PROM code?

Given that you've successfully decompiled the PROM, you're further along than I am - if you've seen any of the posts from Chicago-Joe about this, he had a RM7900-835 CPU on a board, it wouldn't POST, BUT before he read mention of using the terminal to monitor the boot progress he'd had it desoldered again.

I think the pieces of the puzzle all exist, they just need to be collected and assembled to make this work.

[mattst88]

[ruckusman]

Hiya Matt,

I've sent you a PM on irixnet - a thread over there to aggregate the knowledge is probably useful.