Archive for February, 2009

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Reducing Power Through Retiming

February 23, 2009

Here is an interesting and almost trivial technique for (potential) power reduction, which I never used myself, nor seen used in others’ designs. Well… maybe I am doing the wrong designs… but I thought it is well worth mentioning. So, if any of my readers use this, please do post a short comment on how exactly did you implement it and if it really resulted in some significant savings.

We usually have many high activity nets in the design. They are in many cases toggling during calculation more than once per cycle. Even worse, they often drive long and high capacitive nets. Since, in a usual synchronous design (which 99% of us do), we only need the stable result once per cycle – when the calculation is done – we can just put a register to drive the high capacitive net. The register effectively blocks all toggling on that net (where it hurts) and allows it to change maximum one time per cycle.

The image below tells the whole story. (a) is before the insertion of the flop, (b) right after.

low_power_retiming

This is all nice, but just remember that in real life it can be quite hard to identify those special nets and those special high toggling logic clouds. Moreover, most of the time we cannot afford the flop for latency reasons. But if you happen to be in the early design phase and you know more or less your floor plan, think about moving some of those flops so they will reduce the toggling on those high capacitive nets.

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Transparent Pipelining

February 15, 2009

The nice thing about posting in such a site, is that one learns quite a bit with time. During the long pause I took, I tried to read quite a bit and look for some interesting papers. Yes, I am aware that most of my readers are not really interested in reading technical papers for fun, but the bunch that I collected are IMHO quite important and teach a lot.

The one for today is about a novel clocking scheme for latch based pipelines. I found it really interesting and important. I am sure that sometime I am going to implement this for a future design. The paper could have had more examples, and I bet that a few animations would only do good for that topic – but you can’t really ask for stuff like that in a technical paper, can you?

OK, enough of my words – you can find the paper here.

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New Updates Coming Soon

February 4, 2009

I know it has been a while since I added new posts. There has been a lot going on here lately – new addition to the family, new job and some more smaller things, which keep me relatively busy lately.

Don’t give up on me just yet. I promise to keep the interesting posts coming, although maybe not on a weekly basis as I tried doing before.

Hope you guys understand…