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Re: [microblaze-uclinux] minimal microblaze
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
- 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.
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