[time-nuts] Needed: The Real Serial USB Fix

Hal Murray hmurray at megapathdsl.net
Sat Aug 24 07:27:28 UTC 2013


> If it were me, I remove the LCD display.  I don't see a need when everyone
> today has a phone.  the little AVR chip can bit-bang a UDP packet once per
> second and put it on your wifi router.  That cuts the parts cost by 1/3rd
> and the display will be where you can see it, on the phone or computer.

There are still a few of us who don't have cell phones.  :(

I split the problem into two areas:
  Collecting the data
  Displaying it

If I'm collecting data, I want to be able to look back over hours, days, 
months, or even years.  That means I probably want to backup/archive it too.

100 characters of text every 10 seconds is under a megabyte per day.  That's 
small relative to modern disks, medium relative to thumb drives or SD cards 
and small to medium relative to RAM (or ramdisk).  [I generally chop things 
up into a file per day.]

So far, I've always had a handy Linux box running 24x7 when I wanted to 
collect data, so I've never tried to use a smaller system.  Since the data is 
collected on a real system, it's easy to display it any way I like.

I won't be surprised if a project comes along where I want something like a 
small uP to grab careful timing data.  Until then, I'll keep collecting my 
data on a real PC.

------------

Does anybody have data on lifetime of Thumb/SD cards if you flush a log file 
every 10 seconds?

What type of file systems are supported with whatever OS comes with small 
uPs?  Is there any work on flash-friendly file systems for append-only log 
files?

A year or 3 ago, I did some work on logging to ramdisk and occasionally 
copying to hard disk.  The idea was that the hard disk would be spun-down 
most of the time, saving a lot of power.  It didn't save much so I bailed on 
that project.  I assume that means the power to keep the disk spinning is low 
relative to the power to keep the electronics going.  Maybe I just botched 
the experiment.


flushing the file after each line is the simple way to make (mostly) sure 
that your data gets to disk in case the system crashes, but it turns into 
several disk writes each "line".  That's no big deal for a lightly loaded 
hard drive but gets interesting in terms of total writes to flash drives.

You could, of course, fix the code to only do the flush once every N minutes, 
or only when something interesting happens...


-- 
These are my opinions.  I hate spam.






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