Any links to learn about memory cycles and timings?

[Jimbo Mahoney]

I've been scouring the net to find decent links to try to learn about memory timings.

I'm sure many people feel the same way - that memory timings are something of a black art - and it would be nice to have an idea of what the timings actually do and an idea of how to set them.

So far I have the following information for guidelines to set timings for guaranteed stability - i.e. a starting point at which to work down to tighter timings:

tRAS >= tCL + tRCD
or
tRAS >= tCL + tRCD + tRP

(Various sources, which make sense looking at the memory cycle - you don't want tRAS to be too low otherwise it will close too early, leading to data corruption)

tRC = tRAS + tRP
or
tRC = tRAS + tRP + 2

(Various sources)

tRFC = 195/(1000/memory clock speed) for 2GB
tRFC = 327.5/(1000/memory clock speed) for 4GB

e.g. for 2GB @ 400Mhz = 78

This is probably far too high for performance, but be aware the it can be quite critical for stability, especially with more memory.

(Source = http://www.samsung.com/global/busin...ds/applicationnote/app_note_trfc_20040506.pdf)

tREF = 7800/(1000/memory clock speed)

e.g. @ 400 Mhz = 3120

(Makes sense if the memory refresh should be 7.8us, as most are - some modules are 3.9us, so substitute 3900 instead of 7800). Unlike most timings, higher is better in terms of performance.

The secondary timings and how to set them are a complete mystery to me at the moment.

Anyone have any useful links or datasheets or whatever?

EDIT:

tRRD = 10/(1000/memory clock speed)

e.g. @ 400 Mhz = 5

(Source - http://download.micron.com/pdf/technotes/ddr2/TN4709.pdf)