On 5/28/14, 11:06 AM, "Dr. Michael J. Chudobiak" <[email protected]> wrote:
>> asked anyone at TI if it is OK to use the PMU like this? Perhaps you >> should post a question on E2E. > > From http://e2e.ti.com/support/power_management/pmu/f/200/t/185514.aspx: Well, this posting is very interesting. So my thinking is with the addition of a GreenPAK to take care of the corner cases, it would be pretty simple to make a reliable power supply for the BBB. > >"The battery charger should work fine with a supercap. You'll need to >make sure the TS (battery temp sense) pin is at a proper voltage to >allow charging. If the supercap does not have a temperature sensor, you >can simply put a 10k resistor from TS to GND." > > >> If you are charging at 440mA, it will take 50 Seconds to reach full >> charge. What happens when the power fails before that 50 Seconds? I >>would >> recommend that you monitor the supercap voltage and wait until it is >>fully >> charged before opening any files. > >That is why I use full data+metadata journaling on the filesystem. This only reduces the risk of corrupt data, but does not eliminate the possibility. The same concept applies to redundant disks in a RAID. It only minimizes the potential for data loss, but you still have to backup RAID systems. > >If an unclean shutdown happens before the supercap is charged, the next >boot-up will be delayed for several seconds as the filesystem is >repaired using the full journal. That is annoying, but it is a minor >cost for robustness. Mostly, the supercap is there to eliminate the need >for the repair delay. > > >> It is an interesting concept, but I'm still skeptical if this can really >> work. > >Well, I do use it, so that's one data point. > >The other main alternative for bullet-proof power-fail robustness is to >rely on on something like unionfs to provide a mix of read-only and >read/write filesystems, but that's not so simple either. It's complex >and not very well supported in general. > >Batteries have a fairly limited lifetime, so I don't consider that a >practical solution (for me). I agree with you completely and I use supercaps for this reason. > >I'm interested to hear how other people prevent corruption on power >loss, though. My solution is a lot more elaborate with supercap chargers/energy balance, voltage comparators and switchers, boost convertors to keep processor power constant as the supercaps discharge, state machines, etc. Regards, John > > >- Mike > >-- >For more options, visit http://beagleboard.org/discuss >--- >You received this message because you are subscribed to the Google Groups >"BeagleBoard" group. >To unsubscribe from this group and stop receiving emails from it, send an >email to [email protected]. >For more options, visit https://groups.google.com/d/optout. -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
