Re: minimum CA Server requirements

[Andrew Johnson <anj@aps.anl.gov>]

Hi,

On 2011-06-30 Circuit6 Engineering wrote:
> I am very new to EPICS and only just started to work my way through the
> lectures, documentation and program text. I wonder how lean and trim a
> channel access server could be? For example, is it ridiculous to think
> about running CA Server on a 100MHz ARM Cortex-M3 with 256 KB flash
> memory, 64 KB SRAM and 10/100 Mbps Ethernet?

Hmm, interesting question, 256K of Flash and 64K of RAM seems pretty tiny 
nowadays.  I have a pretty minimal CAS program which I build statically on 
Linux; after I strip the binary, the executable is 702KB built for x86_64, and 
817KB built for x86, and that doesn't include all the Linux system libraries.  
I don't know how much smaller an ARM version might be, but I think it most 
likely that the answer is no way with our current code, because you have to 
allow for the rest of the OS as well.

As a comparison, compiling our example IOC application for the RTEMS-mvme3100 
target (a 32-bit PowerPC CPU) results in a 1.6MB bootable binary image (which 
includes the RTEMS OS code).  Now that's not using the same code as the CAS 
program I was discussing above and it is actually a full IOC, but it gives 
another minimal example.  I also looked at the boot images for several of our 
ColdFire-based IOCs here, the bootable image for them are all in the 1.7-1.8MB 
range too.

> I am also very new to RTEMS. If RTEMS is too heavy for a minimal hardware
> environment, could a trim CA server be ported to FreeRTOS with the lwIP
> (Lightweight IP) stack without serious re-engineering?

I think you'd be in the "serious re-engineering" range, although I don't know 
anything about FreeRTOS or lwIP — I'm not saying that porting EPICS would 
necessarily be that hard, but the code volume may be too big to overcome.

HTH,

- Andrew
-- 
Optimization is the process of taking something that works and
replacing it with something that almost works, but costs less.
-- Roger Needham