[uClinux-dev] 2.4.x questions

David McCullough davidm at snapgear.com
Wed Nov 14 21:27:16 EST 2001


Jivin Travis Griggs lays it down ...
> Good news!
> 
> Since we were able to get colilo working with the help from many from 
> this group; we've got the nod to actually use it in our products. We 
> dl'd the modified colilo we submitted a week or so ago, and found a 
> couple of rough left overs; we'll submit the same cleaned up tomorrow.
> 
> We also dl'd the new 2.4 based uClinux and begin putting together 
> development environments and instructions for colleagues. It looks like 
> it has a LOT more options. We had a number of questions though. Most of 
> them had to do with options we encountered as we walked thru make xconfig.
> 
> 1) There's this section at the bottom of the "Processor type and 
> features" menu. We set the FLASH type to AMD. But we left the RAM/FLASH 
> size/bit width set as AUTO. We actually know what the size of each is... 
> but we wondered what the AUTO option does?


It does nothing unless the code underneath it for your platform uses it.
These options are mainly there so that we can all use them.
If you don't know what they are or haven't needed them in the past then
just choose auto.


> 2) In the same menu, there is an option for the Kernel to execute from 
> HIMEM. What is this? Is it the 4K on chip ram found in the 5272? Even 
> more fundamentally, does (and how) uClinux use the on chip ram? Mybe for 
> the stack?

No.  I think this would be for the 68EZ328 guys who run a himem kernel
to save them always having to flash the rom.


> 3) Another menu is the MTD one. If I've got the M5272C3 board, are any 
> of these things going to be useful to me? It seemed like this might give 
> me run time control over the flash ram, but I'm kind of new to this 
> flash stuff.


You could have MTD look after your flash,  but on the M5272C3 we do not
have the flash configured in so people don't trash their dmon loader ;-)

You can also use the blkmem driver to look after flash.


> 4) In the Application Configuration>>Core Applications menu, we enabled 
> netflash and recover for grins. We found that when we then tried to 
> 'make', it could build neither of these. Cursorily it seemed that it 
> couldn't find zlib.h. Is this a known problem?


A bug in the Makefiles doesn't setup the includes for zlib on the user
build.  In the config.arch you need to add:

	INCZ    = -I$(ROOTDIR)/lib/zlib

to the UCLINUX_BUILD_USER section and and also:

	-L$(ROOTDIR)/lib/zlib

to LDPATH.

> 5) Finally, we had built a little network client/server pair which timed 
> how long it took to transmit 4MB of image data over the ethernet. With 
> the older (2.0 based version) and a 2.2 kernel for the host box, we were 
> seeing transmit times of ~1.9 seconds. One of the reasons we got excited 
> about the 2.4 based uClinux, is we thought this time might improve a 
> little. It did the opposite. The host box is running 2.4.(12 I think). 
> With the 2.4 based uClinux, our xmit times go up to ~2.4 seconds. Is 
> there a known reason for this? A setting we can flick somewhere which 
> will improve performance at least back to the ~1.9?


Unlikely,  the 2.4 network stack does quite a lot more than the 2.0 stack
while externally achieving the same thing :-)  It's also the source of
quite a bit of code size increase in the kernel over 2.0.

A sample that last 2-2.5 seconds is probably not a good basis for true
performance.  You could be affected startup/shutdown differences.  You need
to get the test time out to 30 - 60 seconds to be more confident in the
difference.  I will not be surprised if it is little slower.

Cheers,
Davidm
-- 
David McCullough:    Ph: +61 7 3435 2815  http://www.SnapGear.com
davidm at snapgear.com  Fx: +61 7 3891 3630  825 Stanley St., W'gabba QLD 4102, Oz
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