Re: [microblaze-uclinux] minimal microblaze

[John Williams <jwilliams@xxxxxxxxxxxxxx>]

Hi Emanuel,

emanuel stiebler wrote:

> What are the "minimal"  requirements on a usefull microblaze system
> running uClinux ?
> 
> Talking about RAM / Flash , or ...

This is a complex question:

  - if you can get the kernel to XIP (execute in place) then it will 
save a lot of RAM (maybe 700K?).  This could be done with a fairly 
simple modification to the link script mbvanilla.ld and some changes in 
the startup code in mbvanilla.c.  Bootloader changes would also be 
necessary.

  - similarly if you can leave the romfs image in flash, it will further 
reduce the RAM requirements.  This could be done in a similar manner to 
the kernel XIP.

Accessing kernel code and filesys from flash may take a performance hit, 
although instruction and data caches will claw some of that back.

  - if you run completely from RAM (including kernel and ROMFS image), 
then 1 meg should be enough to bring up the kernel and a shell, but not 
much room left for anything useful.

I think if you had say 1Meg RAM (2 is better!) and 2 Meg flash, with 
kernel XIP and romfs in flash, you could do some useful work. It might 
be worth asking about this on the main uclinux-dev list as well (or 
searching their archives).

> P.S. John, you had the uClinux running on the SRAM of the P160 module at 
> one time, right ? Which would put the minimal RAM configuration to 1 
> MByte ?

Yes, but I moved to the DDR once I hit that 1MByte ceiling.  I haven't 
spent any effort optimising the footprint.  You could probably test this 
out by modifying arch/microblaze/mbvanilla.ld to set the kernel base 
address (the OPB memory block at the top) to the address of the SRAM - 
0xffe00000 IIRC.  Also then modify include/asm-microblaze/xparameters.h 
and change the memory parameters in there to suit.  You'd also need to 
tweak the addresses in the bootloader, so it knows where to copy the image.

Hope this helps.

John

___________________________
microblaze-uclinux mailing list
microblaze-uclinux@itee.uq.edu.au
Project Home Page : http://www.itee.uq.edu.au/~jwilliams/mblaze-uclinux
Mailing List Archive : http://www.itee.uq.edu.au/~listarch/microblaze-uclinux/