A PowerMac G5 rarity: explicit fatal kernel trap (data storage interrupt) instead of Copyright notice and boot text

[Mark Millard]

On G5 PowerMac's (with lots of RAM) I frequently have boots that after clearing (going black) never display anything from where the Copyright notice should display on --and the fans gradually spin up indicating that it failed somehow.

Rarely an error message shows up instead of the Copyright and later boot text. This happend today and I wrote the one generated down so that I could leave a note about it. I've no clue how to repeat it in any reasonable time frame.


The text on screen was (not a copy of the detailed spacing):

fatal kernel trap
exception       = 0x300 (data storage interrupt)
virtual address = 0x2fb1948
dsisr           = 0x40000000
srr0            = 0x88fa84
srr1            = 0x9000000000003030
lr              = 0x8903e8
curthread       = 0xd0ccc0
pid = 0, comm =

Panic: data storage interrupt trap
cpuid = 0
KDB: stack backtrace
#0: 0x533d30 at ??+0
#1: 0x86346c at ??+0
#2: 0x864630 at ??+0
#3: 0x8595e0 at ??+0
Uptime: 1s


If I interpret what I found about this correctly the dsisr value indicates that the data's address was not-found in primary or secondary "page table entry group"s (so a page fault occurred that was not expected to need to be handled): indicated by DSISR[1] = '1'...

> Set if MSR[DR] = ’1’ and the translation for an attempted access is not found in the primary page table entry group (PTEG), or in the secondary PTEG (page fault condition); otherwise cleared. 
Context: FreeBSD FBSDG5S0 10.0-STABLE FreeBSD 10.0-STABLE #0 r268571: Sun Jul 13 06:28:19 UTC 2014     root at grind.freebsd.org:/usr/obj/powerpc.powerpc64/usr/src/sys/GENERIC64  powerpc

===
Mark Millard
markmi at dsl-only.net