Kevin Hilman <khilman@xxxxxxxxxxxxxxxxxxx> writes: > Blazej Kot <bjk45@xxxxxxxxxxx> writes: > >> I have been working with the linux-pm kernel on the Gumstix Overo, >> seeing how low it's power consumption can go, both during the cpu "on" >> and especially while the CPU is suspended. Thus far, I've had some >> disappointing results, the best I could get is about 500mW while on, >> and 250mW while suspended (ie by running "echo mem > /sys/power/ >> state"). I am led to believe that the OMAP processor is capable of >> much lower power consumption during standby. >> >> I am wondering if anybody in the gumstix community is looking into the >> software support for very-low-power modes on the overo. If so, I am >> wondering what the lowest power levels are which you have reached >> during standby are. >> >> I have seen this: >> >> http://markmail.org/message/ge5hec5f5asp7a67#query:omap%20linux >> %2080%20ma+page:1+mid:t2erlwweknakm767+state:results >> >> Which seems to indicate the lowest power reached is 80mA at 3.3V -> >> 0.264 W, which is about what I'm seeing. Is it really true that the >> overo draws a quarter of a watt when doing absolutely nothing? > > There are lots of factors involved. > > The current OMAP PM branch is focused on minimizing power consumed by > the OMAP SoC itself. However, there are lots of other things on-board > (audio codecs, regulators, WiFi chipsets etc.) that can consume power > that we may not be currently managing in the omap kernel. > > I don't have an Overo so am not familiar with all the on board > peripherals, but you should probably do some experiments where you > can put all the on-board devices into low-power/off states and > run some experiments as well. > > In the case of the Beagle results you referenced, I'm pretty sure it > is something on board that is drawing the ~80mA and not on-chip. I > assume this because setting the OMAP to use OFF-mode in suspend or > idle results in the drop of a few mA reflecting an expected drop in > power consumed by OMAP itself, but still leaving lots of power > consumed. > > For example, testing today's PM branch on Beagle gives me roughly the > same numbers as the post you referenced, but slightly better: > > - boot idle: 323 mA > > - screen blank: 216 mA > # echo 3 > /sys/class/graphics/fb0/blank > > - suspend (OMAP retention): 75 mA > # echo mem > /sys/power/state > > - sleep-while-idle: 75 mA - this same power state as suspend, > but happens in idle > # echo 1 > /sys/power/sleep_while_idle > > - suspend (OMAP off): 72 mA > # echo 1 > /sys/power/enable_off_mode > # echo 1 > /sys/power/voltage_off_while_idle > > Ultimitately the answer is that more work needs to be done with the > using the regulator framework and/or the drivers for the on-chip > peripherals to be sure they can be powered off when needed. > After digging a little more in the beagle forums, someone has already done the work to confirm that it is indeed board level design and issues that are drawing the rest of the power on Beagle. There's a thread[1] in the beagleboard list about how to get down to 8mW power on Beagle, but it does require hardware changes. This should shed some light on the types of things you'd probably have to do for Overo. Kevin [1] http://groups.google.com/group/beagleboard/browse_thread/thread/197a8ef6b46cc828/6e98db4cbe2cebaa?# -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
