Another try at the run-from-Flash issue for MPC8xx/MBX/custom

[Doug Rogers <rogers@innocon.com>]

I, too, would like to run from Flash. The question for me isn't speed,
isn't cost, nor EMI effects. It is simply a matter of size. We have a
very small area in which to squeeze the parts, and the best we could do
is 32M RAM and 16M ROM. Our application code is in the 10M range (text
only, even after chopping over half of it out!), but it is expected to
grow. So for us it's not really a matter of cost or (running) speed,
since the Flash runs fast enough for our purposes.

As another constraint, our card needs to be able to run very soon after
power-up. I've hacked the LynxOS startup monitor to detect either gzip'd
or bzip2'd KDI's. I've timed the decompression of our smaller test image
and it takes over 40 seconds on a 40MHz MBX860 board. That's too slow.
We could live with 20, perhaps, but not much more than that. For now I
boot my images over the network since our MBX board has only 4M Flash.
It's faster than decompressing!

With LynxOS, we're able to keep in Flash both the text sections of the
kernel AND of all binaries on the filesystem. Wow! That allows us to put
only the RAM disk and vector/data/bss sections into RAM. Shweet!

I was hoping that Linux was to that point, but apparently not. Just
having the kernel run from ROM would be helpful for now, so if anyone
out there has done so, I'd be very appreciative of any feedback.

Thanks!

Doug

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