What does this script do? [Perl]

Question

Hi.
First, an absolutely necessary foreword:
I'm planning to buy a ThinkPad T410s. It has a nice special battery chip, making it possible to have much better means of power management.
For instance, one can put in an additional (so called "Ultrabay") battery and the special kernel module "tp_smapi"
(read more about it here: http://www.thinkwiki.org/wiki/Tp_smapi) lets one take control of how it is handled (see below)
The thing is, the default behavior is to drain ultrabay completely, but this causes its capacity to deplete quickly. That's why there are certain tp_smapi's options like "force_discharge" which tell the laptop to ex. drain main battery first, the use ultrabay battery. But it is quite a hassle to manually switch to ultrabay when main runs out, etc.
That's why such script has been created:
http://www.thinkwiki.org/wiki/Talk:Code/tp-bat-balance
It's supposed to manually switch main and ultrabay back and forth to ensure exual discharge all the time, as I understand it.
But I cannot use it in my laptop if I am not 100% sure what it does! It is not really documented, and I'm not a coder.
Understanding bash scripts isn't really rocket science, but with Perl, it is much different.
So I kindly ask you:
Could you please, in normal english describe what it does? (ex. which condition needs to be met to execute a specific command)
Thanks in advance!
PS.: And if you do, I could put the description into ThinkWiki's tp-bat-balance site, so that everybody (not only Perl programmers) know what it does

Answer 1

i no longer have the script open (and i don't feel like reopening) so this is from memory...
warnec wrote:1) how is $thresh defined? What is it supposed to do in these two funtions? Why is it added?
$thresh is defined by the simple `my $thresh = 3` line that you quoted to me.  I assume it's there so that the script doesn't switch batteries the instance that BAT0 hits 99.999%, then back when BAT1 hits 99.998%, then back again when BAT0 hits 99.997% and so on, and so on.
warnec wrote:$bat_remaining[0] > $bat_remaining[1] + $thresh
$bat_remaining[1] > $bat_remaining[0] + $thresh
the first statement means if battery zero's remaining percent is greater than (battery one's remaining percent plus 3), then...; and the second statement is just the reverse, if battery one's remaining percent is greater than (battery zero's remaining percent plus 3), then....  if neither of these statements are true, then the threshold his not met (the two battery's percentages are within 3% of each other) and no battery switching should happen.
warnec wrote:
2) why such a weird (at least to me) syntax?
set_force_discharge(0,1);
set_force_discharge(1,0);
set_force_discharge(0,0);
set_force_discharge(1,1);
set_force_discharge takes two arguments.  the battery to set (BAT0 or BAT1) and the value to set it to (0 = don't discharge, 1 = discharge).
so, the above statements would be equivalent to:
tell BAT0 to discharge
tell BAT1 to not discharge
tell BAT0 to not discharge
tell BAT1 to discharge
which is exactly what you need to do depending on the results of your if statements.
Last edited by brisbin33 (2010-06-14 21:48:57)