[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [f-cpu] Powersave-function



On Wed, 13 Jun 2001, Andreas Romeyke wrote:

> IMHO it is possible to simple include powersave functions into F-CPU.
> We need only a special instruction and a programmable register/flag which
> switches units on or off (bring it in tristate or decouple it from bus and
> vcc)...
> 
> All units should be easily extended with this feature, is not it?

Easiest way to do power saving is clock gating. In CMOS logic only
transitions consume power so removing the clock reduces the power
consumption. Leakage is another problem with low voltage processes if
ultralow power consumption is needed. For leakage there are quite many
tricks, for example more complex gates or better internal protocols etc.

But clock gating is not always trivial. Normal timing tools have usually
small problems if the clocks are gated and static timing analysis is not
so straightforward. Also as far as I know there are some tricks how to
remove the gating and not cause glitches to the clocks. Also some
blocks can need few clocks to stabilize and that must be tought out in the
powerup logic etc.

I think it is easier to first do the chip and then think about power
saving. Unless the chip consumes too much power and the power drain must
be reduced. But there are easier ways to do this in the beginning. For
example I/O lines should not be toggled unnecessarily and same applies to
internal signals. Quite often the designs have default values for the
busses and they have unnecessary toggling from
old_value->default_value->new_value.

=============================================================================
Mr. Kim Enkovaara   | kim.enkovaara@iki.fi | Microelectronic Riemannian
Vasamatie 1 C 16    | IRC: embo            | curved-space fault in
02630 Espoo         |                      | write-only file system

*************************************************************
To unsubscribe, send an e-mail to majordomo@seul.org with
unsubscribe f-cpu       in the body. http://f-cpu.seul.org/