Rockbox mail archive
Subject: Re: DRAM 2MB -> DRAM 8MB
From: Vladimir Pantelic (pan_at_nt.tu-darmstadt.de)
Warp Dag wrote:
> Actually I don't agree at all!!!
> Just think 5 minutes ;)
Actually I thought more than that :-)
> Filling a 2MB or a 8MB buffer while the hard
> drive is spinning takes about the same time!!! I mean, for a song,
Point for you.
> Finally, about your average power consuption calculation is flawed. Here
> is the correct formula (I assume the drives will never take more than 4s
> to fill the 8MB buffer):
> 2 MB : 50mA + 300mA * 2/100 + 500 * 3/100 = 50mA + 21mA = 71mA average
> 8 MB : 50mA + 300mA * 4/450 + 500 * 3/450 = 50mA + 6mA = 56mA average
OK, so it's 56 and not 59.
As I said my numbers were "rough". I just wanted to point out that N x
larger buffer does not mean N x longer playing time and that the key to
power saving is to reduce the current used when the drive is not
spinning. An Archos JBR runs about 12hours with 1800mAh batteries, so we
could assume that it takes an average of 1800 / 12 = 150mA. With the
drive currents as given above and some allowance for not draining the
batteries completely we should have a constant current of about 100mA at
least, so the reduction through 8MB of buffer might be even less as above:
2MB: 100mA + 21mA = 121mA
8MB: 100mA + 6mA = 106mA --> 14% less !
> But you know, you should not think in "average". Because the idea is
> that it will reduce the spinning stuff, and you must know that each time
> you take a heavy load on the cells you loose a lot of energy, more than
OK on this one too. I'm sure we'll soon know how much longer the 8MB
unit will run. It will be interesting to see whether the theory will
match real life.
Page was last modified "Jan 10 2012" The Rockbox Crew