Re: [9fans] Plan9 on QNAP TS-212 NAS (kw)

[ron minnich <rminnich@gmail.com>]

well, to elaborate on this.

Long ago, you probed by just reading memory until you read back
nothing but ffffffffffffffffff. That was a memory hole. Then somebody
at one chipset vendor got clever and broke this test. Oops, you have
to figure out if maybe your test is failing because somebody got
clever.

You can in fact figure out memory size on many systems by reading
registers in configuration space. On K8/K10/whatever, you can write
code to probe the famous "1f" configuration space and read out memory
bank info. Core 0 can read it for ALL cpus. I've written this and then
lost it :-) but it's pretty easy.

Of course, many vendors view such info as "crown jewels" so this is
hardly a universal solution.

You can, if you want to get really weird, use the I2C bus to probe all
installed DDR and figure it out. Silly that the OS has to do this when
the BIOS does it but hey ... it's a PC ... of course it's gross.
Reference code for MANY chipsets is available in coreboot.

But I agree with Erik: frequently memory slots are more of a headache
than a bonus.

ron