[uClinux-dev] 2.4.x questions

Greg Ungerer gerg at snapgear.com
Thu Nov 15 19:53:20 EST 2001


Hi Travis,

Travis Griggs wrote:
> Greg Ungerer wrote:
> <snip>
> > Currently the 4k internal RAM is not used by uClinux.
> <snip>
> 
> No kidding?

No, seriously :-)


> Is it hard to change this?

No, not really. Depends on exactly what you want to use it for.
It would be pretty easy to map it onto the end of the current
DRAM, which would mean it would be part of the initial kernel
stack.

Problem is that uClinux is a pretty large code base, 4k don't
equate to much in the big picture. You would be better using
it for a critcal section of code/data for your sepecific
application. And that means you will need code to setup and
use it in a way to give you best performance.


> I'm really very new (naive) to
> all of this low level stuff. I am told that the SDRAM on the C3 board is
> not 0 wait state (he didn't remember exact value off the top of his
> head, he thot maybe 3). The on chip is 0. It would seem like a good idea
> to park the on chip ram right behind the SDRAM, and then let the stack
> grow down from their. I don't really know how deep the stack usually is,
> but my thot was that it might spend a good part of its time in the
> faster ram.

Good theory. Problem is with uClinux that their is many stacks.
Each process has its own application level and kernel level
stack.


> On a related note I guess, when we start doing our own boards, I've been
> told that they're going to make them similiar to the C3, but will put in
> 512K fast static 0 wait state ram? How will I ensure that uClinux uses
> that by preference?

Well, you need to decide what to use it for first. It is easy to
tack it on the end of DRAM. But that gives you no real control
of what runs in it, or when...

Regards
Greg


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Greg Ungerer  --  Chief Software Wizard        EMAIL:  gerg at snapgear.com
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