homemade EFIS system and EMI

In article et,
UltraJohn wrote:
Pete Schaefer wrote:

He could also go with the Athena card instead. That does have VGA on it.
And it's a faster processor.

"Evan Carew" wrote in message
...
Well, it doesn't come with a video card if that is what you meant,
however, that is a relatively simple matter to fix. PC104 video cards
are quite reasonably priced & even support 1/2 or 1/4 VGA standards.

Looking closer at it the biggest shortcoming I see now is the lack of ram
the card only handles 32mb and Linux is very memory intensive and running

With some care in kernel tuning, you can get the memory footprint *way* down.

The _real_ memory pig is the X server.

With a text-only display, it is *amazing* how much you can do in 'small'
memory configurations. 8 megs is _plenty_ for running a dedicated 'firewall'
box, for example, and a _386DX/33_ will handle a full T-1, in that
application, with cycles to spare.

I ended up ordering a Via TC motherboard as it will take up less space
than the CL with cumbersome DC converter and hopefully reduce RFI, and
if there is still RFI I have only one variable to contend with vs two.

I did not go with the PC104 format although I did look at this at
length. I already have considerable experience with the VIA now, a case
and airplane bay designed for it (17cm x 17cm) and a very lean kernel
tweaked for it. Also the VIA is a tad more mainstream with this
typically resulting in better doc and support for drivers. Also I can
boot off a write protected USB flash card (USB flash memory as IDE did
not work for me, too much data corruption in unexpected power off
scenarios). I don't know which PC104 have this ability. Anyone with
PC104 experience would probably argue with this, but I have had my fair
share in the past of getting odd behavior with a video, sound, ethernet
driver and having to slowly track it down. I know all the MB sensors on
the VIA are queryable in linux (ie CPU temp, all the voltages, etc..)

For me, memory is very important and 512Mb a mininum. Why so big when
my entire custom Linux distribution with X and Java fits on a 128Mb USB
flash card? As a Robert pointed out the kernel is a small memory
consumer, X is the real hog. And with potentialy complicated displays
this would grow even further.

Most importantly this distribution runs in entirely in memory,
there are no writes by the OS to the main USB flash card which is write
protected. As such there is no swap space, and hence any malloc calls
need to actually find real memory not virtual memory. Flash memory
degrades with each write, areas such as swap and log directories can
receive an enormous # of writes with often little effort. Some
benchmarks have shown corruption after only 10,000 writes. Having a
memory block go bad (which is just a matter of time given the nature of
Flash) can lead to odd/unpredictable behavior (the worse kind),
something I want to entirely avoid.

The secondary USB flash card, which is not write protected, holds the
log files and mp3 files. 'Non critical' files. I also wrote the data
logging program to only flush the OS writes every X seconds, not on
each log write. I could add an OS swap file to this partition but I
still could end up with corrupted swap space and the additional writes
would also shorten the life of the USB flash card. Additional memory is
cheap insurance (in additional $40) in avoiding these problems and has
an added benefit of performance.

If I was going to start from scratch I might go with the PC104 platform
but neither platform seems to be vastly superior to the other. And the
Devil you know...

jcpearce wrote:

I ended up ordering a Via TC motherboard as it will take up less space
than the CL with cumbersome DC converter and hopefully reduce RFI, and
if there is still RFI I have only one variable to contend with vs two.



Nice write up of what your thinking is. As you said probably either system
could work but your more familiar with this avenue.
This has been a very positive thread with no would getting there"panties up
there crack" g.
I'd be interested in any updates your might have, I have already bookmarked
your web site and will check in from time to time.
I wanted to check on the cost of the Athena system unfortunately they
require you to log in and register for a quote, I wasn't that
interestedvbg.
Good Luck
John

I think the Athena goes for around $600.

"UltraJohn" wrote in message
ink.net...
I wanted to check on the cost of the Athena system unfortunately they
require you to log in and register for a quote, I wasn't that
interestedvbg.

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JC,

For what its worth, the previously described PC104 486 based system was
used by my company to controll a filter system & write to an X display
at the same time running Linux. That system only had 128MB of RAM & that
might have been too much. All applications ran from RAM.

The problem with X apps that run on Linux is that when they are
developed with a toolkit such as Motif or GNOME, you end up including
quite a lot of baggage along with the X app. One way to solve this is to
search for a "light" toolkit or to simply write your app in plain X
yourself. People often say of Such apps "Hey your X app really starts
fast!" That being said, you should not be surprised when X sucks 50% of
the performance of your CPU up on such a box.

On my production unit, the X Application was the only one running &
didn't need a desktop. Under the hood, my drivers supplied the needed
data to the X app. Hopefully, it goes without saying that the kernel was
a custom striped down version with my drivers & very little else.

Evan
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Evan Carew wrote:

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JC,

For what its worth, the previously described PC104 486 based system was
used by my company to controll a filter system & write to an X display
at the same time running Linux. That system only had 128MB of RAM & that
might have been too much. All applications ran from RAM.

Good points Evan. A lot can be done if you set up a custom system. Up until
I switch to an AMD 64 bit system I ran slackware in which you can select
indiviual packages to install. You could get a very small system if you
wanted. Stick to on editor one window system and a custom kernel and you
can get a rather complete system pretty small.
Take a look at most 'Boxed' systems under /bin /sbin /usr/bin and /usr/sbin
and you will see a lot of programs that you will never use!
John