Tyan S2895 7.1 amd64 >8Gb RAM support? - resolved

[Karl Pielorz]

Hi,

I finally resolved this... (posted to the list for completeness / incase 
someone else hits this issue).

Brief Solution: Reduce dram timing in the bios from DDR400 to DDR333.

Gory details: Having taken quite a trip through mptables, bioses, pulling / 
pushing DIMM's etc. - all the DIMM's in the machine are DDR400 rated - all 
do test OK.

Also remember this machine was used for years under WinXP64/Vista 
(including using things like a 6Gb RAM drive for video production) - if it 
had been corrupting data as much as under FreeBSD it would have been 
noticed :(

Anyway, it transpires earlier Opterons were either incapable of running 
DDR400, or had a 'caveat' that when running lots of memory modules they 
recommended dropping the timing from DDR400 downwards. This was 
'apparently' fixed in later Opterons (my system has 2 * E Stepping 285's). 
To counter this the BIOS would detect which CPU was in use, and drop the 
maximum memory speed accordingly vs. installed DIMM slots.

This restriction was apparently lifted for Opteron 285's (at least for the 
stepping I'm using) as their onboard memory controller should be capable of 
driving all memory banks, at DDR400 speeds - the BIOS reflects this by 
defaulting to DDR400 timing for my system.

Obviously, this works on this system under Windows memory usage patterns / 
loading / stress - but not for FreeBSD's memory usage / loading.

With the RAM backed down to DDR333 - the system once again runs flawlessly.

RAM tests didn't catch this - as I could only effectively test 4Gb of RAM 
'at a time' - I also doubt that the memory usage patterns software such as 
memtest86 use would 'load' the memory system enough to cause the timing 
problem.

Max Laier did say he'd had to make memory timing adjustments on his S2895 
system, but I presumed that with DDR400 rated memory, and the BIOS using 
the SPD details on the chips (all branded RAM) that it wouldn't be that 
(and the fact windows gave years of service with the current settings).

-Kp

[Who now knows far more than I ever wanted to about mptables, APIC, ASL and 
hopefully a whole bunch of other stuff I can forget now ;)]