Re: [oc] Regarding the low power bus encoding research ?

[John Sheahan <jrsheahan@optushome.com.au>]

On Fri, Nov 29, 2002 at 09:14:14PM +0100, nico wrote:
> Before regarding switching activity, you must think about clock gating
> of the register use for the bus. Clock tree are 70% of the power
> consumption of a chip. 

70% is too high for the clock tree. 30% perhaps.
Are you including the flipflop clock related power in the clock 
tree numbers?

> 
> If you think of register configuration each little
> flip-flop receive the clock, you could have hundred of them. But
> such registers only need the clock in writing. And configuration write
> are very uncommon. So write signal should be used to mask/unmask the
> clock of such register bank.
> 
> Maybe an other way could be investigate : enable the clock of the module
> the time to process a bus request. When playing with the clock, you
> could have some chicken&eggs problem. It's easy to shut up the clock,
> but impossible to reneable it without external help.
> 
> Maybe the bus could provide a clock enable signal. And a system could
> let run the clock 16 or more cycles after this signal goes low (the
> slave IP are wake up by external access but shut it-self down).


clever clock gating does help power a lot. Its hard to do well. It makes
static timing harder. 

Regarding dta busses
minimizing toggling will help power, particularly if implemented with
clock gates.  but you have to know the data patterns to minimize the
toggling of course. Which is pretty design specific.

for example a gray coded counter makes just over half as many edge
transitions as a binary counter, but (I suspect) the same number if the
address distribution is random.
john


> 
> nicO
> 
> On Wed, 27 Nov 2002 09:24:14 +0800
> NansonHuang@itri.org.tw wrote:
> 
> > 
> >  Hi,
> > 
> >  I am now surveying the papers how to achieve the on-chip low power
> >  bus.
> > Most of them are focus on decorrelating/encoding the bus data to
> > reduce the switching activity. There are a lot of work on it. However,
> > I am not sure if there are any
> > commerical on-chip bus standard SoC product(Wishbone, AMBA, Sonic.etc)
> > utilizing
> > the low power encoding scheme. In others words, does it work to lower
> > the power consumption in SoC ? Coud anyone give me some ideas to let
> > me know if I will go on further ?
> > 
> >  All the best,
> > 
> >  Nanson
> > 
> > 
> > 
> > --
> > To unsubscribe from cores mailing list please visit
> > http://www.opencores.org/mailinglists.shtml
> > 
> > __________________________________________________
> > Modem offert : 150,92 euros rembours_s sur le Pack eXtense de Wanadoo
> > ! Haut d_bit _ partir de 30 euros/mois :
> > http://www.ifrance.com/_reloc/w
> --
> To unsubscribe from cores mailing list please visit http://www.opencores.org/mailinglists.shtml
--
To unsubscribe from cores mailing list please visit http://www.opencores.org/mailinglists.shtml