Re: [microblaze-uclinux] Minimum memory footprint?

[John Williams <jwilliams@xxxxxxxxxxxxxx>]

Hi Greg,

Greg Watson wrote:

> We are just considering porting uClinux to a Xilinx V2Pro (+microBlaze) 
> board that we have under development.
> 
> The board only has 2MB RAM available to the CPU (3MB if really essential).
> 
> The only drivers needed would be a UART and a TCP stack, plus any other 
> drivers that are essential (Interrupts?).
> 
> The board has no flash so we would write the boot image to RAM (via the 
> PCI bus) and then, I assume, reset the processor. After booting, we 
> would want to run a single application.
> 
> So before we leap into this project we'd like to know if we are utterly 
> wasting our time with just 2MB RAM.

Sounds reasonable to me.  You can certainly boot a board with 2MB of 
memory (it's been done in under 1MB!), and your narrow requirement for 
just a single application means you can trim out a lot of userspace 
cruft that you won't need.

Ultimately I think your limiting factor will be the runtime memory 
footprint and requirements of your application - only you can estimate this.

With no effort at all you can make a kernel with tcp/ip support in about 
1.2Meg, but trimming stuff out (at the kernel config level, not code 
hacking) you could probably get that down to 1 meg.

Since you'll have network stupport, you could potentially mount your 
entire root filesystem via NFS, so there's no filesystem overhead on 
your board. All memory not used by the kernel is available to your 
applications.

Memory fragmentation may be an issue for long uptimes - but if you are 
only running one application, and it can stay "alive" for extended 
period, again that may not be a problem - just something to be aware of.

Note of course you can prototype on any existing board with heaps of 
memory, just limit the memory size visible to the kernel.  Now you can 
experiment on the effect of a low memory ceiling before you get your 
hardware.

Bottom line, I think it's definitely worth a go.

Cheers,

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/