Re: [microblaze-uclinux] Minimum memory footprint?

[Greg Watson <gwatson@xxxxxxxxxxxx>]

John,

Thanks for the reply. That sounds very promising. Our app footprint is 
not more then 200kBytes so we should be OK.

Off to build some hardware now....

Regards

Greg Watson



John Williams wrote:
> 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
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