[mythtv-users] Stop / Start Athcool just Befor / After a Recording

[f-myth-users at media.mit.edu]

    Date: Wed, 23 Nov 2005 12:33:22 -0500
    From: Erik Karlin <e_karlin at yahoo.com>

    you could just hijack the channel change "script" functionality and
    create a user job when the recording completes. The problem of
    back-to-back recordings is still possible. maybe some clever file
    locking scheme between a channel change (start) and user job (end) could
    do the trick.

[There's nothing out there that looks at CPU utilization and leaves
low-power mode if the CPU suddenly looks busy?  Or is the problem
latency?  Laptops do this kind of CPU cycling all the time...  Or
is it that the CPU never looks busy, but recordings are messed up
even so, if done in powersave mode?]

Here's a totally gross idea, but it might work, and could be done with
a tiny shell script.  Assume we start from the powersave state.  The
script loops, once per second, checking the mod-date of the recordings
directory itself.  If it changes, immediately go to non-powersave state.

Once in that state, check every so often (once a minute?) to see if
any file in the recordings dir has been modified.  (You can't just
check the mod-date of the dir itself, as in the previous paragraph,
because once the file has been created, the mod-date of the dir itself
won't change.)  If nothing's been modified in the last minute, assume
we're done for the moment and go back into powersaving.  This check is
probably cheap (since the dir info is presumably cached in RAM), but
it still may not be as cheap as checking just the dir-mod date itself,
which is why I mention using the dir-mod check in the fast loop (1 Hz)
and the slightly-slower check in the slow loop (1/60 Hz).

You could script this pretty trivially just using things like "find"
and asking it to find files newer than a reference file (which you
touch upon entering each of the two states and which had better not
be in the recordings dir itself... :)

This also assumes you can afford to be in powersave mode for the first
second of any given recording.  [If you can't, you could always just
enter fast mode for hh:mm:59..hh:mm+1:01 (two seconds) every minute---
since recordings presumably always start on a minute boundary---and
then run the fall-back-to-powersave check during that.  Might cause
your fan to whoosh in one-minute cycles, though...]  This scheme does,
at least, provide some hysteresis, so you won't leave the fast-CPU
state until you're really sure you're done recording.  And if anything
else is modifying stuff there (like transcoding maybe?), you'll stay
in fast-mode until it's done.

It would definitely be better if there were hooks for MythTV actions,
though, since using an event-driven style to control this would be
much more reliable and less of a kluge than the polling method above.