On Mon, 8 May 2017, David Woodhouse wrote: > > I've got a problem with the underlying mechanism. How long does it take to > > erase a NAND block? A couple of milliseconds. That means that for an erase > > to be "weak" du to a power fail, the host CPU must issue an erase command, > > and then the power to the NAND must drop within those milliseconds. > > However, in most systems there will be a power monitor which will > > essentially reset the CPU as soon as the power starts dropping. So in > > practice, by the time the voltage is too low to successfully supply the > > NAND chip, the CPU has already been reset, hence, no reset command will > > have been given by the time NAND runs out of steam. > > > > Sure, with switchmode power supplies, we don't have those large capacitors > > in the power supply which can keep the power going for a second or more, > > but still, I would think that the power wouldn't die fast enough for this > > to be an issue. > > > Our empirical testing trumps your "can never happen" theory :) I'm sure it does. But what is the explanation then? Has anyone analyzed what is going on using an oscilloscope to verify relationship between erase command and supply voltage drop? /Ricard -- Ricard Wolf Wanderlöf ricardw(at)axis.com Axis Communications AB, Lund, Sweden www.axis.com Phone +46 46 272 2016 Fax +46 46 13 61 30 -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
