On Sun, 16 Apr 2017 19:42:50 +0000, Gordon Henderson wrote:

> In article ,
> Frank Miles   wrote:
>>On Fri, 14 Apr 2017 19:25:11 +0100, Ahem A Rivet's Shot wrote:
>>
>>> On Fri, 14 Apr 2017 16:30:48 -0000 (UTC)
>>> Frank Miles  wrote:
>>>
>>>> I have an embedded application for the RPi-3.  Unfortunately it's likely
>>>> that uses will remove power without properly shutting the RPi down.
>>>> Therefore I've got a 'power-going-down' bit of hardware which sets a GPIO
>>>> bit causing a proper shutdown.  The question, of course, is how long does
>>>> a shutdown take?
>>>
>>>  It depends - mostly on how fast the SD card is, how many dirty
>>> buffers need to be flushed and how long processes take to die. Best bet is
>>> to measure it under your worst case loads with the card you intend to use
>>> and add a healthy safety factor.
>>
>>Ok, reframing :
>>  What's the easiest way to detect when shutdown is complete?
>
> Some boards use the serial Tx line. This is set low when shutdown is
complete.

I'll take a look at that too once I get my tech to make me the power cable
with separable conductors needed for monitoring the current consumed.  I'm
also curious to see how much current the RPi consumes once it is shut-down
(since it reboots after some 10s or so it must be running, at a minimum, some
kind of timer/clock).

> Other strategies are to minimise SD card writes during normal use, but we
> don't know what the application is.. However stuff I do is things like
> remove logging (like rsyslogd - no idea how to stop systemd writing to
> SD card, I don't use it), mounting /tmp/ as ramdisk (see /etc/defaults/shm )
> and generally tuning application to minimise writes, if possible.
>
> Gordon

It's running a GUI that controls a research instrument.  The only disk activity
is very infrequent, to save altered instrument configuration/settings.  At this
point (the users may come up with changes in the future), there's no data
logging.

Excellent idea to kill any syslog activities, etc., thanks!

    -F

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