> > (when DPM is enabled). This should, by all documentation, > reduce the power consumption of the CPU. > > But does it reduce the energy consumed per instruction > executed, or increase it? In theory if you do not issue instructions to the units, DPM turns themselves off saving (from some Freescale doc on the subject) around 6% power (while running benchmark code). Every pipeline bubble adds to the power saving! :] Then the theory goes that if you can force the units to sit idle for 1-255 instructions you can save more. I have no idea if it actually works.. that is what I wanted to find out. > see any improvement in energy per instruction unless you can > reduce the CPU core Vdd voltage. It doesn't improve energy per instruction, so much as allow the units to go into low-power states so while there are no instructions being fetched, you aren't wasting power. > If you can't reduce the energy per instruction then you might > as well "race to idle", which is effectively what we do currently. Like I said that is what I wanted to find out. Let me find that Freescale doc.. http://www.freescale.com/files/32bit/doc/app_note/AN2436.pdf -- Matt Sealey <matt at genesi-usa.com> Manager, Genesi, Developer Relations
