Accessing Few DDR Ranks

Linux and Unix-Like Linux
1

Hi,

Considering a case there are 4 RANKs in a DIMM. Run time, if one of the 4 rank has fault which results into use 3 ranks. Say Rank1 has faults. So Rank0, Rank2 and Rank3 are operational.

  1. Is it possible case?
  2. If above is true then, who is responsible for address aliasing? Memory Controller or Operating System/Software.

Physically now, there are 3 ranks, so less size.

Dhaval

2

Is this a homework question?

3

No.
We are developing Memory Controller and came across this case and I am not sure about this.

Dhaval

4

In short - there is no good way to know ahead of time. For example, a Sun m4000 showed a memory fault, one memory chip out of 8 on a bank was bad. The OS "ignored" it and tried to function with the 15 remaining. An earlier sun box (a Sun v445 I think) with a similar problem disabled an entire bank and spewed massive warnings.

The point being the result result of a fault is hardware, OS, and OS version (fault management module) dependent.

So - There is no one generic answer AFAIK. Linux runs on many platforms. It even runs my refrigerator at home.

5

So if there is faulty rank in middle. There will be address aliasing.

Who manages address aliasing, memory controller or os?

Dhaval